"The Oldest Stone Tools Yet Discovered Are Unearthed in Kenya"
Approximately 3.3 million years ago someone began chipping away at a rock by the side of a river. Eventually, this chipping formed the rock into a tool used, perhaps, to prepare meat or crack nuts. And this technological feat occurred before humans even showed up on the evolutionary scene.
That’s the conclusion of an analysis published today in Nature of the oldest stone tools yet discovered. Unearthed in a dried-up riverbed in Kenya, the shards of scarred rock, including what appear to be early hammers and cutting instruments, predate the previous record holder by around 700,000 years. Though it’s unclear who made the tools, the find is the latest and most convincing in a string of evidence that toolmaking began before any members of the Homo genus walked the Earth.
“This discovery challenges the idea that the main characters that make us human—making stone tools, eating more meat, maybe using language—all evolved at once in a punctuated way, near the origins of the genus Homo,” says Jason Lewis, a paleoanthropologist at Rutgers University and co-author of the study.
Up until now, the earliest clear evidence of stone tools came from a 2.6-million-year-old site in Ethiopia. An early human ancestor called Homo habilis likely made them. Similar “Oldowan style” tools, known for choppers with one refined edge, have been discovered at several other sites in East and Southern Africa.
The common assumption has been that as Africa’s climate changed and forest canopies gave way to savannas, early hominins diversified and the Homo genus—the line that would produce modern humans—emerged, around 2.8 million years ago. With new environments came new food sources and a need for tools to process those foods. Grassland may have provided ample sources of meat, plants and nuts, while the forest provided shade and cover to prepare them.
But scientists have started to poke holes in that line of thinking. In 2010, researchers found fossilized animal bones in Kenya dating to 3.4 million years ago with cut marks on them—possibly made from a stone tool, though still controversial. Australopithecus afarensis (Lucy’s species) was the only human ancestor or relative around at the same time and place. Another hominin, Australopithecus africanus, appears to have had a grip strong enough for tool use. Studies show chimpanzees use rocks as hammers or anvils on their own in the wild, and, with a little guidance, bonobos are capable of creating stone tools.
Back in July of 2011, Lewis teamed up with his wife and co-author Sonia Harmand, an archaeologist at Stony Brook University, to lead a field expedition in Kenya for the West Turkana Archaeological Project. They were looking for artifacts similar in age to a controversial 3.5 million-year-old species discovered by Meave Leakey’s group years earlier.
But, the survey team took a wrong turn and ended up at a site now called Lomekwi 3 in dried river ravine. “To us it was immediately a very interesting area,” notes Harmand, “with outcrops and erosive cuts, you could see what was normally hidden by the sediment.” So, they spread out and started looking.
Just after teatime, a radio call came in: Someone had spotted a series of strange stones sticking out of the sediment. Scars cut into the stones set them apart from run-of-the-mill rocks. “You can tell these scars are organized,” says Harmand. The rocks had been hit against one another to detach flakes, a process called knapping. Based on geological records for the area, the artifacts had to be at least 2.7 million years old. “We had no champagne that evening, but we were very happy,” Harmand recalls.
“I've seen the altered rocks, and there is definitely purposeful modification of the stones by the hominins at the Lomekwi site 3.3 million years ago,” says paleoanthropologist Rick Potts, director of the Smithsonian’s Human Origins Program, who was not affiliated with the study. Potts notes that while the study is exciting, it also raises a lot of big questions.
Among them, how are these new artifacts related to the Oldowan tools? The short answer is no one knows. “We've jumped so far ahead with this discovery, we need to try to connect the dots back to what we know is happening in the early Oldowan,” says Harmand.
What’s perhaps most intriguing about the Lomekwi tools is who made them, why and how.
Further analysis of the markings on the tools and attempts to replicate their production suggests two possible ways: The toolmaker might have set the stone on a flat rock and chipped away at it with a hammer rock. Or, the toolmaker could have held the stone with two hands and hit it against the flat base rock. “It’s very rudimentary,” says Harmand.
(The early humans who made the Oldowan tools used an entirely different method: putting a rock in each hand and striking them together with just the right force at just the right angle—which would have required more dexterity.)
As for who, the species identified by Meave Leakey’s group, Kenyanthropus platyops, is a prime suspect. If that’s true, or if the Lomekwi tools were made by another species outside the human genus, some of the same factors that drove our evolution might also have driven the evolution of other distant cousins.
But, Lewis and Harmand aren’t ruling out the possibility that an unknown member of the human genus once inhabited the area and made the tools. “That's a different but equally interesting story, in which our genus evolved half a million years before, and in response to completely different natural selective pressures, than we currently think,” says Lewis.
Whoever made these tools was somehow motivated to hit two rocks together. Why exactly remains a mystery.
"Why Humans Don’t Have Tails"
Our primate ancestors used their tails for balance as they navigated treetops, but around 25 million years ago, tailless apes started appearing in the fossil record. How and why some primates like humans lost their tails is largely a mystery, but a new study suggests a single genetic mutation may be responsible for the sudden change.
“This question, ‘Where’s my tail?,’ has been in my head since I was a kid,” says study co-author Bo Xia, a graduate student NYU Grossman School of Medicine, to Carl Zimmer of the New York Times. Xia was further motivated to investigate the question after he injured his coccyx, the small triangular bone humans and some apes have at the base of their spine. “It took me a year to recover, and that really stimulated me to think about the tailbone," he says.
To find out how and why humans lost their tails, Xia and his colleagues examined the early stages of embryonic development, during which certain genes are switched on and off. Those genes control the formation of different parts of a skeleton.
Scientists had already identified 30 different genes fundamental to tail development in other animals, reports Tibi Puiu for ZME Science, so the study authors suspected a genetic mutation or two might have erased humans’ tails. They compared the DNA of six species of tailless apes to nine species of tailed monkeys to find a mutation that apes and humans share, but monkeys lack. Eventually, their search led them to a gene called TBXT.
To see if the mutation could be linked to the loss of a tail, the team genetically tweaked mice to have the same TBXT mutation that humans have. When researchers made the genetic edit, many rodents didn’t grow tails, while others grew short ones.
Although it’s impossible to definitively prove that this single mutation is responsible for the disappearance of our tails, “it’s as close to a smoking gun as one could hope for,” says Cedric Feschotte, a geneticist at Cornell University who was not involved in the study, to the New York Times.
The discovery suggests our ancestors lost their tails suddenly, rather than gradually, which aligns with what scientists have found in the fossil record. The study authors posit that the mutation randomly might have cropped up in a single ape around 20 million years ago, and was passed on to offspring. Perhaps being tailless was a boon to the apes, and the genetic mutation spread like wildfire.
“For something to be lost in one big burst is really significant, because you don’t then have to posit millions of years of successive tiny changes accumulating gradually,” says Carol Ward, an anthropologist at the University of Missouri who wasn’t involved in the work, to the New Scientist’s Michael Le Page. “It may tell us why all of a sudden when we see the apes [emerge], they have no tails.”
"Scientists describe earliest primate fossils"
A new study published Feb. 24 in the journal Royal Society Open Science documents the earliest-known fossil evidence of primates.
A team of 10 researchers from across the U.S. analyzed several fossils of Purgatorius, the oldest genus in a group of the earliest-known primates called plesiadapiforms. These ancient mammals were small-bodied and ate specialized diets of insects and fruits that varied by species. These newly described specimens are central to understanding primate ancestry and paint a picture of how life on land recovered after the Cretaceous-Paleogene extinction event 66 million years ago that wiped out all dinosaurs — except for birds — and led to the rise of mammals.
(...) The team analyzed fossilized teeth found in the Hell Creek area of northeastern Montana. The fossils, which are now part of the collections at the University of California Museum of Paleontology, are estimated to be 65.9 million years old, about 105,000 to 139,000 years after the mass extinction event. Based on the age of the fossils, the team estimates that the ancestor of all primates —including plesiadapiforms and today’s primates such as lemurs, monkeys and apes — likely emerged by the Late Cretaceous and lived alongside large dinosaurs.
“It’s mind blowing to think of our earliest archaic primate ancestors,” said Wilson Mantilla. “They were some of the first mammals to diversify in this new post-mass extinction world, taking advantage of the fruits and insects up in the forest canopy.”
The fossils include two species of Purgatorius: Purgatorius janisae and a new species described by the team named Purgatorius mckeeveri. Three of the teeth found have distinct features compared to any previously known Purgatorius species and led to the description of the new species.
Purgatorius mckeeveri is named after Frank McKeever, who was among the first residents of the area where the fossils were discovered, and also the family of John and Cathy McKeever, who have since supported the field work where the oldest specimen of this new species was discovered.
“This was a really cool study to be a part of, particularly because it provides further evidence that the earliest primates originated before the extinction of non-avian dinosaurs,” said co-author Brody Hovatter, a UW graduate student in Earth and space sciences. “They became highly abundant within a million years after that extinction.”
“This discovery is exciting because it represents the oldest dated occurrence of archaic primates in the fossil record,” said Chester. “It adds to our understanding of how the earliest primates separated themselves from their competitors following the demise of the dinosaurs.”
Elpistostege: le poisson qui avait des doigts
Extraits de cet article:
L’examen d’Elpistostege, fascinant poisson fossile de Miguasha, révèle que ses nageoires contenaient des doigts. Une information capitale, mais qui brouille la frontière entre poissons et vertébrés terrestres…
Une chauve-souris qui déploie ses ailes grâce à ses longs doigts filiformes. Un aye-aye, petit primate nocturne de Madagascar, qui déloge une larve dans une branche à l’aide de son majeur long et gracile. Un raton laveur qui tripote sa nourriture dans un cours d’eau avec ses petites mains griffues. Un journaliste scientifique qui tape son article sur son clavier. Sur le thème de la main, l’évolution a fourni une pléthore de variations.
Mais d’où vient-elle, cette main ? Et surtout, quand est-elle apparue ? Parfois réduite à un ou deux doigts, comme dans l’aile de l’oiseau ou la patte du cheval, ou carrément escamotée chez les serpents, elle est quand même présente dans l’histoire évolutive des reptiles, amphibiens, oiseaux et mammifères, bref de tous les vertébrés terrestres, qu’on rassemble sous l’appellation de « tétrapodes ». En fait, toutes les pattes ont un même ancêtre, avec toujours la même structure de base.
La « main » a fait son apparition quelque part durant la transition qui a vu des poissons coloniser la terre ferme. Pendant longtemps, cette transition est restée couverte d’une chape de mystère. Mais un fossile de poisson, découvert en Gaspésie, vient enfin apporter quelques bribes d’information. Son nom : Elpistostege. Sa particularité : il avait des doigts !
Trouvé en 2010 dans les fameuses falaises fossilifères du parc national de Miguasha, le fossile est celui d’un poisson prédateur qui mesurait 1,57 m de long et qui devait régner en maître dans un estuaire maintenant disparu. Sa découverte, annoncée en 2013, avait fait grand bruit, en le classant comme le poisson le plus proche des tétrapodes. Mais une récente étude, parue dans la revue Nature, révèle de plus que l’animal possédait, bien cachés dans la chair de ses nageoires, des doigts.
« Les osselets sont petits, de l’ordre du millimètre, mais leur disposition les uns par rapport aux autres saute aux yeux : ils sont organisés comme des doigts. » C’est avec fascination que Richard Cloutier raconte ce qu’il a vu dans les nageoires pectorales de «son» Elpi. Le paléontologue, professeur à l’Université du Québec à Rimouski, côtoie la bête depuis sa mise au jour par des employés du parc.
Travail de moine
Passé au tomodensitomètre, le fossile avait déjà livré une grande partie de son intimité. « Mais les nageoires représentent un défi : relativement petites, très aplaties, recouvertes de rayons, constituées d’os minuscules… Il nous a fallu une grande minutie et des astuces algorithmiques pour découvrir ce qu’elles renfermaient. » L’article, rédigé conjointement avec John Long de l’Université Flinders d’Adélaïde, en Australie, et plusieurs autres collaborateurs, est le fruit d’un travail de moine.
Pourquoi tant d’efforts ? C’est que la transition entre les poissons et les tétrapodes est l’une des plus importantes de toute l’histoire de l’évolution. Elle a permis la colonisation de la terre ferme par les vertébrés et a mené à une diversification spectaculaire des formes de vie, des amphibiens aux oiseaux en passant par les mammifères, dont les humains, sans oublier des millions d’espèces disparues comme les dinosaures. Comprendre les mécanismes subtils de cette transition est fondamental, et la transformation de la nageoire en membre est justement ce qui distingue les premiers tétrapodes de leurs ancêtres poissons.
En effet, au premier coup d’œil, les plus anciens tétrapodes connus sont peu différents des poissons qui les ont précédés. Les paléontologues en ont trouvé quelques espèces. Les plus anciens à mériter le titre, justement parce qu’ils possèdent des doigts sans équivoque, déambulaient sur Terre il y a 365 millions d’années. Les espèces fossiles Ichthyostega et Acanthostega, toutes deux de l’est du Groenland, ou encore Tulerpeton, de Russie, sont les plus vieux tétrapodes dont on dispose. Sortes de grosses salamandres, ils ont des « mains » composées d’un nombre variable de doigts, parfois jusqu’à huit (un nombre qui se fixera à cinq plus tard dans l’évolution).
De l’autre côté, les poissons fossiles qui ressemblent le plus à des tétrapodes ne sont pas légion. On compte trois espèces : Elpistostege, de Miguasha, Panderichthys, de Lettonie, et Tiktaalik, de l’Arctique canadien. Elles ont toutes pataugé dans les eaux il y a environ 375-380 millions d’années. Et toutes les trois ont des nageoires certes fortes, mais munies de rayons, comme des poissons « ordinaires ». Ensemble, elles forment le groupe des elpistostégaliens.
« Entre paléontologues, nous nous entendons sur le fait que ces elpistostégaliens ont fort probablement donné naissance aux tétrapodes, explique Richard Cloutier. Les dates coïncident, le scénario tient. Mais entre les premiers et les seconds, il y a un trou de 10 à 15 millions d’années pour lequel nous n’avons pas de fossiles. On passe d’une nageoire plutôt “poisson” à une patte très “tétrapode”. Les détails de la transition entre les deux nous manquent. On a enfin un début de réponse avec Elpistostege. »
Déjà des phalanges ?
Les examens de tomodensitométrie ont dévoilé une constellation de petits os dans la nageoire de la bête. Ils sont placés en rangées, comme les sièges d’un auditorium. Leur nombre augmente un peu d’une rangée à l’autre, à mesure qu’on s’éloigne du corps de l’animal ; un os d’une rangée s’articulant à deux os parallèles dans la rangée suivante, comme les branches d’un arbre qui se ramifient. Rien de très innovant – on trouve ce patron dans les nageoires d’autres poissons fossiles. Mais là où Elpistostege se distingue, c’est à l’extrémité de la « main ». « On a vu deux os qui étaient chacun prolongés par un os unique. L’équivalent de la première phalange de nos doigts. Ça peut paraître insignifiant, mais c’est du jamais-vu dans une nageoire fossile de cette époque », indique Richard Cloutier.
Même s’il manque encore des étapes évolutives intermédiaires, le chercheur trace des parallèles avec la patte du tétrapode Tulerpeton. Les carpes (ou os du poignet), les métacarpes (os de la paume) et la première phalange de deux doigts apparaissent à son écran. La reconstitution, en 3D, tournoie et montre dans toute sa splendeur une patte en devenir.
Selon Richard Cloutier, ce détail est suffisant pour remettre en question l’appellation « poisson » chez cet animal. « Il a les os crâniens d’un tétrapode, des caractéristiques de tétrapode sur ses vertèbres, un palais de tétrapode et maintenant des doigts. À partir de combien de détails anatomiques concordants pouvons-nous classer un animal parmi les tétrapodes ? Ma perception des choses, c’est qu’Elpistostege n’est pas un poisson très proche des tétrapodes. Il est un tétrapode », conclut le chercheur avec un sourire un peu provocateur.
Une hypothèse qui fait effectivement réagir. À Perth, en Australie, la Québécoise Catherine Boisvert, chercheuse à l’Université Curtin, a publié une étude en 2008, aussi dans la revue Nature, dans laquelle elle présentait une description de la nageoire pectorale de Panderichthys, le cousin letton d’Elpistostege. « Nos analyses au tomodensitomètre avaient permis de voir la présence de petits os à l’extrémité de la nageoire de l’animal, mais nous n’avons vu que la première rangée d’os. » Rangée que Richard Cloutier considère comme l’homologue des carpes de notre poignet.
« Mais la puissance de notre appareil à l’époque ne permettait pas une résolution aussi précise qu’aujourd’hui. Peut-être y a-t-il d’autres os plus petits au bout de ceux-ci qui nous ont échappé… Mais même s’il y en avait eu, tout repose ensuite sur l’interprétation qu’on en fait. La mosaïque de petits os d’Elpistostege peut bien contenir des protodoigts, mais dans les faits, on n’en sait rien. Il ne suffit pas de dire que des os qui s’articulent bout à bout sont des doigts pour qu’ils en soient. »
Une critique qu’elle n’est pas la seule à formuler. « Les réviseurs de notre article nous ont reproché de proposer une nouvelle définition du doigt qui nous permettait ensuite d’affirmer qu’Elpi en possédait et donc qu’il était un tétrapode, se rappelle Richard Cloutier. Mais c’est l’inverse : les nouvelles informations fournies par le fossile nous ont enfin permis de préciser ce qu’est un doigt. Il existait plusieurs définitions dans la littérature ; nous l’avons clarifiée. Il faut quand même s’entendre sur une définition si l’on veut avancer. »
À l’Université Drexel de Philadelphie, Edward Daeschler approuve. Avec Neil Shubin, de l’Université de Chicago, il est à l’origine en 2006 de la découverte et de la description du fameux Tiktaalik, l’autre cousin d’Elpi, de l’Arctique. « La définition du doigt proposée par Richard Cloutier est une très bonne définition. Une série d’os qui ne bifurquent pas, cela a le mérite d’être simple et clair. Et son interprétation des images obtenues me semble crédible. »
Il faut savoir qu’un fossile passé au tomodensitomètre ne donne pas une image nette et parfaitement contrastée. La différence de densité entre les os fossilisés, donc minéralisés, et les sédiments qui les entourent est souvent trop subtile pour l’œil. Et la compaction de tout cela n’aide en rien, surtout pour des ossements si petits. C’est pourquoi il faut l’aide de logiciels d’analyse d’image et de visualisation 3D. Mais comment être sûr qu’aucune structure n’est une « hallucination » produite par le logiciel ? « Trois personnes ont traité les données avec trois logiciels différents basés sur des algorithmes différents, sans voir ce que les autres faisaient, relate Richard Cloutier. Les résultats ont été les mêmes. »
D’où la confiance d’Edward Daeschler. « Elpistostege avait effectivement des doigts. Mais était-ce un tétrapode pour autant ? Là-dessus, mon interprétation diverge. On a encore affaire à une nageoire recouverte d’écailles, et surtout de rayons, comme un poisson. Ma définition d’un tétrapode implique la perte des rayons. Sinon, on ne peut pas parler d’un “membre”. »
Zones grises
Sachant que tous ces éléments sont enchâssés dans une nageoire, comme dans une mitaine de chair prise dans un sandwich de rayons, peut-on effectivement parler de doigts et de main ? « Pourquoi pas ? relance Richard Cloutier. Prenez la nageoire de la baleine. Même s’ils ont perdu leur indépendance et leur mobilité, les doigts sont toujours là, à l’intérieur. Faut-il lui enlever son statut de tétrapode pour autant, sachant qu’elle descend d’animaux terrestres ? Quant aux fossiles d’Acanthostega du Groenland, leurs doigts sont clairement développés, mais nous ignorons s’ils étaient libres de bouger ou s’ils étaient pris dans une “mitaine” du vivant de l’animal. Cela ne nous empêche toutefois pas de les considérer indiscutablement comme des tétrapodes… »
« Tout est une question de définitions dans notre domaine, admet Edward Daeschler. La nature se moque de l’endroit où l’on met la barrière entre les poissons et les tétrapodes. Ce sont des enfantillages de paléontologues. Elpistostege et Tiktaalik étaient des poissons dotés de nageoires charnues et de plusieurs caractéristiques de tétrapodes. Acanthostega, lui, était un tétrapode, mais il avait encore des branchies et un mode de vie très aquatique. On le voit bien, l’évolution est un continuum et les transitions, même si elles semblent rapides à l’échelle géologique, ont pris du temps. Mais les zones grises sont inconfortables et l’on aime bien mettre les choses dans des cases définies. »
« On est un peu comme les paléoanthropologues, compare Catherine Boisvert. Ils essaient depuis toujours de cibler un moment précis pour fixer l’apparition de l’espèce humaine sur la base de trop peu de fossiles. On argumente sur l’apparition des doigts chez les tétrapodes à partir d’un seul individu fossilisé. Vivement qu’on trouve davantage de fossiles d’animaux encore plus près des tétrapodes et qu’on puisse voir si ces petits os sont toujours là… et s’ils sont bel et bien les précurseurs de nos doigts ! »
Attentes futures pour bestioles du passé. Sur la question de l’apparition de la main, peut-être qu’un jour les paléontologues avanceront main dans la main.
L'assassinat de Tzihuacpopocatzin
With the death of Motecuhzoma II at the hands of the Spaniards, and of Cuitlahuac by way of smallpox, it was Cuauhtemoc who was elected to assume the role of Tlatoani and chief defender of the city of Tenochtitlan. However, as the Spaniards and their allies gradually gained a foothold in the basin and began to cut off the metropolis from its allies and resources, his position as ruler was becoming increasingly untenable. Discord amongst the nobility was brewing as a small but ever increasing faction of pipiltin composed primarily (and supposedly) of the sons of Motecuhzoma II, chief amongst them the Cihuacoatl Tzihuacpopocatzin, began to argue for a conciliatory approach towards the Spaniards, some going so far as advocating to submit themselves as tributaries to the would-be conquerors.
Much like Tlaxcallan before them, conflict within the ranks of the Mexica regarding the course of action towards the Spaniards threatened to destabilize the polity, but it was ultimatly the military and priestly class that got their way. Thus, the purge to eliminate the subversive elements of the pipiltin class commenced as Cihuacoatl Tzihuacpopocatzin, Cipactzin, Tecuecuenotzin, Axayacatl II and Xoxopehuáloc were promptly assassinated, and the course for Tenochtitlan was firmly set towards war; the Tlatoani’s reign secure… for now.
"Study claims to identify the homeland of all modern humans"
Is there a specific location on Earth where humans like us originated? A new study pinpoints an area called the Makgadikgadi-Okavango wetland, shared by the modern-day countries of Botswana, Namibia and Zimbabwe in southern Africa as the birthplace of modern humans (Homo sapiens sapiens) about 200,000 years ago.
Scientists from the Garvan Institute of Medical Research discovered that the earliest ancestors of humans appeared in that area and lived there for about 70 thousand years. Eventually, they were forced to expand their domain by the climate changes in Africa.
The study lead Professor Vanessa Hayes from the Garvan Institute of Medical Research, who is also associated with the University of Sydney and the University of Pretoria, highlighted the significance of their find:
“It has been clear for some time that anatomically modern humans appeared in Africa roughly 200 thousand years ago,” said Hayes. “What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors.”
For their study, the scientists focused on examining the mitochondrial DNA of modern-day residents of the area. Hayes explained that “Mitochondrial DNA acts like a time capsule of our ancestral mothers, accumulating changes slowly over generations.” This fact allowed the researchers to compare the DNA code (or mitogenome) of different people to figure out how closely related they are.
The scientists were able to use collected blood samples to put together a much improved catalogue of the mitogenomes of early humans.
The study’s first author Dr. Eva Chan from the Garvan Institute of Medical Research, who led the phylogenetic analyses, expanded on their methodology:
“We merged 198 new, rare mitogenomes to the current database of modern human’s earliest known population, the L0 lineage,” said Chan, adding “This allowed us to refine the evolutionary tree of our earliest ancestral branches better than ever before.”
The researchers looked at the L0 lineage timeline in combination with distributions of various sublineages based on language, culture and geography. What they found is that the maternal lineage of humanity emerged in what they dubbed a “homeland’ area south of the Greater Zambezi River Basin region. This “homeland” includes all of northern Botswana stretching into Namibia to the west and Zimbabwe to the east.
Why was this area so perfect for humans to develop? According to research by the geologist Andy Moore of Rhodes University, that area once contained Lake Makgadikgadi – Africa’s largest-ever lake system. Once the lake started to drain due to shifts in the tectonic plates underneath, it left behind a fertile wetland, which was favorable for sustaining life.
The ecosystem was home to the early humans for 70K years until about 130 to 110 thousand years ago, when people started venturing out northeast and southwest from the area, while a group stayed in the area (with their descendants still found there today).
Why did many people leave the “homeland,” which today is actually one of the largest salt flats in the world? Climate change simulations from the study’s co-corresponding author Professor Axel Timmermann, Director of the IBS Center for Climate Physics at Pusan National University, point to shifts in rainfall which created “green, vegetated corridors” leading out of the area. These allowed the human ancestors to leave the homeland and look for greener pastures elsewhere.
“These first migrants left behind a homeland population,” pointed out Professor Hayes. “Eventually adapting to the drying lands, maternal descendants of the homeland population can be found in the greater Kalahari region today.”
Not everyone is on board with the scientists’ findings. Mark Thomas, an evolutionary geneticist at the University College London, said in an email to National Geographic that “The inferences from the mtDNA data are fundamentally flawed.” He also called the study “storytelling.”
But others, like University of Hawaii at Manoa geneticist Rebecca Cann, who was a reviewer of the study and has carried out her own pioneering work on mitochondrial DNA, supports the study, saying while the study is “not perfect”, it will move the science along and “stimulate a lot of new studies.”
Des outils d’au moins 650 000 ans au Gabon
Quel âge ont-elles ? Les pierres taillées découvertes dans une ancienne terrasse fluviale du fleuve Ogooué au Gabon ne sont pas datables directement. Régis Braucher, du CEREGE à Aix-en-Provence, et Prosper-Prost Ntoutoume Mba, de la cellule scientifique de l’Agence nationale des parcs nationaux du Gabon, et leurs collègues viennent d’estimer leur durée d’enfouissement à au moins 650 000 ans, ce qui fait remonter la première industrie lithique du bassin du Congo au Paléolithique inférieur africain.
"Supernovae and life on Earth appear closely connected"
A remarkable link between the number of nearby exploding stars, called supernovae, and life on Earth has been discovered.
Evidence demonstrates a close connection between the fraction of organic matter buried in sediments and changes in supernovae occurrence. This correlation is apparent during the last 3.5 billion years and in closer detail over the previous 500 million years.
The correlation indicates that supernovae have set essential conditions for life on Earth to exist. This is concluded in a new research article published in the scientific journal Geophysical Research Letters by senior researcher Dr. Henrik Svensmark, DTU Space.
According to the article, an explanation for the observed link between supernovae and life is that supernovae influence Earth's climate. A high number of supernovae leads to a cold climate with a significant temperature difference between the equator and polar regions. This results in strong winds and ocean mixing, vital for delivering nutrients to biological systems. High nutrient concentration leads to a larger bioproductivity and a more extensive burial of organic matter in sediments. A warm climate has weaker winds and less mixing of the oceans, diminished supply of nutrients, lower bioproductivity, and less burial of organic matter.
"A fascinating consequence is that moving organic matter to sediments is indirectly the source of oxygen. Photosynthesis produces oxygen and sugar from light, water and CO2. However, if organic material is not moved into sediments, oxygen and organic matter become CO2 and water. The burial of organic material prevents this reverse reaction. Therefore, supernovae indirectly control oxygen production, and oxygen is the foundation of all complex life," says author Henrik Svensmark.
In the paper, a measure of the concentration of nutrients in the ocean over the last 500 million years correlates reasonably with the variations in supernovae frequency. The concentration of nutrients in the oceans is found by measuring trace elements in pyrite (FeS2, also called "fool's gold") embedded in black shale, which is sedimented on the seabed. Estimating the fraction of organic material in sediments is possible by measuring carbon-13 relative to carbon-12. Since life prefers the lighter carbon-12 atom, the amount of biomass in the world's oceans changes the ratio between carbon-12 and carbon-13 measured in marine sediments.
"The new evidence points to an extraordinary interconnection between life on Earth and supernovae, mediated by the effect of cosmic rays on clouds and climate," says Henrik Svensmark.
The link to climate
Previous studies by Svensmark and colleagues have demonstrated that ions help the formation and growth of aerosols, thereby influencing cloud fraction. Since clouds can regulate the solar energy that can reach Earth's surface, the cosmic ray/cloud link is important for climate. Empirical evidence shows that Earth's climate changes when the intensity of cosmic rays changes. Supernovae frequency can vary by several hundred percent on geological time scales, and the resulting climate changes are considerable.
"When heavy stars explode, they produce cosmic rays made of elementary particles with enormous energies. Cosmic rays travel to our solar system, and some end their journey by colliding with Earth's atmosphere. Here, they are responsible for ionizing the atmosphere," he says.
On a marché en Amérique
Newly discovered fossil footprints show that humans were present in North America between ~23,000 and 21,000 years ago during the Last Glacial Maximum, according to recent research in Science.
"Cause of worst mass extinction ever found"
Dinosaurs are the most infamous victims of a mass extinction event 66 million years ago. But an even worse extinction happened 251.9 million years ago.
Called the end-Permian mass extinction or the Great Dying, this most severe of extinction events wiped out about 90 percent of the planet’s marine species and 75 percent of terrestrial species. While scientists long have suspected it was initiated by volcanic eruptions in what is now Siberia, until now they haven’t been able to explain exactly how so many species died out.
A new paper published in Nature Communications lays out the case that nickel particles that became aerosolized as a result of eruptions in the Siberian Traps region became dispersed through the air and water and were the cause of the ensuing environmental catastrophe. The paper pinpoints huge Norilsk nickel sulfide ore deposits in the Tunguska Basin that “may have released voluminous nickel-rich volcanic gas and aerosols into the atmosphere” as the start of the chain of events that led to the mass extinction.
The study is based on analysis of nickel isotopes that came from late Permian sedimentary rocks gathered from the Buchanan Lake section in the Sverdrup Basin in the Canadian High Arctic. What’s notable about the rock samples is that they featured the lightest nickel isotope ratios ever measured, leading the scientists to conclude that the nickel came in the form of aerosolized particles from a volcano.
As the paper outlines, the only comparable nickel isotope values would be those from volcanic nickel sulfide deposits. The scientists write that of all the mechanisms that could result in such values, “the most convincing” explanation is that they got there as “voluminous Ni-rich aerosols” from the Siberian Traps large igneous province (STLIP).
The deadly effect of nickel particles
When the nickel got into the water, it wreaked havoc on the underwater ecosystem.
Co-author of the study, associate professor Laura Wasylenki of Northern Arizona University, explained that “nickel is an essential trace metal for many organisms, but an increase in nickel abundance would have driven an unusual surge in productivity of methanogens, microorganisms that produce methane gas. Increased methane would have been tremendously harmful to all oxygen-dependent life.” This would have affected living creatures in and out of the water. The professor believes their data offers direct evidence that links nickel-rich aerosols, changes to the ocean, and the mass extinction that followed. “Now we have evidence of a specific kill mechanism,” she added.
Other theories on the Great Dying
Previous studies have pointed to other effects of the Siberian volcanic eruptions that likely contributed to the extinction event, including an overall warming of the planet, release of toxic metals, and acidification of the oceans, which likely killed off a number of species quickly. Others died out as a result of the depleted oxygen levels in the water.
“This domino-like collapse of the inter-connected life-sustaining cycles and processes ultimately led to the observed catastrophic extent of mass extinction at the Permian-Triassic boundary,” said marine biogeochemist Hana Jurikova of the University of St. Andrews in the UK, who carried out a 2020 study on the end-Permian extinction. Her study looked at fossil shells from brachiopods in what is now the Southern Alps in Italy.
"Triassic Dinosaur Footprints Discovered in Wales"
Paleontologists have discovered the footprints of large sauropodomorph dinosaurs on the shoreline near Penarth in south Wales, the United Kingdom.
The Penarth footprints are part of the Blue Anchor Formation and date from the Late Triassic epoch, over 200 million years ago.
The total exposed surface is about 50 m long and 2 m wide, and is split into northern and southern sections by a small fault.
The tracks occur on a single surface at the top of a 15-cm-thick gray, dolomitic siltstone. Small gypsum nodules occur near the top of the bed.
The tracks are deeply impressed into the top surface and are partially infilled with a green siltstone with orange stringers.
The impressions are highly variable in shape and size. They are all highly weathered, exhibiting both broken and smoothed surfaces, breakage being facilitated by numerous diaclases in the bedding plane.
They are roughly circular to elliptical in outline, and almost entirely lack clear impressions of either individual digits, claws or footpads.
The footprint outlines are highly irregular, but some impressions do reveal possible anatomical information. They range over 20-60 cm in maximum diameter. Depth is likewise variable, but ranges mainly over 5-10 cm.
“We believed the impressions we saw at Penarth were consistently spaced to suggest an animal walking,” said Professor Paul Barrett, a paleontologist in the Department of Earth Sciences at the Natural History Museum, London.
“We also saw displacement rims where mud had been pushed up. These structures are characteristic of active movement through the soft ground.”
Professor Barrett and his colleagues from the United Kingdom and France think that the Penarth footprints are an example of the ichnogenus Eosauropus, which is a name not of a dinosaur but a type of track thought to have been made by a sauropodomorph dinosaur.
“We know early sauropods were living in Britain at the time, as bones of Camelotia, a very early sauropod, have been found in Somerset in rocks dated to the same period,” said Dr. Susannah Maidment, a paleontologist in the Department of Earth Sciences at the Natural History Museum, London.
“We don’t know if this species was the track maker, but it is another clue which suggests something like it could have made these tracks.”
“These types of tracks are not particularly common worldwide, so we believe this is an interesting addition to our knowledge of Triassic life in the UK,” Professor Barrett said.
“The record of Triassic dinosaurs in this country is fairly small, so anything we can find from the period adds to our picture of what was going on at that time.”
"Earliest human remains in eastern Africa dated to more than 230,000 years ago"
The age of the oldest fossils in eastern Africa widely recognized as representing our species, Homo sapiens, has long been uncertain. Now, dating of a massive volcanic eruption in Ethiopia reveals they are much older than previously thought.
The remains—known as Omo I—were found in Ethiopia in the late 1960s, and scientists have been attempting to date them precisely ever since, by using the chemical fingerprints of volcanic ash layers found above and below the sediments in which the fossils were found.
An international team of scientists, led by the University of Cambridge, has reassessed the age of the Omo I remains—and Homo sapiens as a species. Earlier attempts to date the fossils suggested they were less than 200,000 years old, but the new research shows they must be older than a colossal volcanic eruption that took place 230,000 years ago. The results are reported in the journal Nature.
The Omo I remains were found in the Omo Kibish Formation in southwestern Ethiopia, within the East African Rift valley. The region is an area of high volcanic activity, and a rich source of early human remains and artifacts such as stone tools. By dating the layers of volcanic ash above and below where archaeological and fossil materials are found, scientists identified Omo I as the earliest evidence of our species, Homo sapiens.
"Using these methods, the generally accepted age of the Omo fossils is under 200,000 years, but there's been a lot of uncertainty around this date," said Dr. Céline Vidal from Cambridge's Department of Geography, the paper's lead author. "The fossils were found in a sequence, below a thick layer of volcanic ash that nobody had managed to date with radiometric techniques because the ash is too fine-grained."
As part of a four-year project led by Professor Clive Oppenheimer, Vidal and her colleagues have been attempting to date all the major volcanic eruptions in the Ethiopian Rift around the time of the emergence of Homo sapiens, a period known as the late Middle Pleistocene.
The researchers collected pumice rock samples from the volcanic deposits and ground them down to sub-millimeter size. "Each eruption has its own fingerprint—its own evolutionary story below the surface, which is determined by the pathway the magma followed," said Vidal. "Once you've crushed the rock, you free the minerals within, and then you can date them, and identify the chemical signature of the volcanic glass that holds the minerals together."
The researchers carried out new geochemical analysis to link the fingerprint of the thick volcanic ash layer from the Kamoya Hominin Site (KHS ash) with an eruption of Shala volcano, more than 400 kilometers away. The team then dated pumice samples from the volcano to 230,000 years ago. Since the Omo I fossils were found deeper than this particular ash layer, they must be more than 230,000 years old.
"First I found there was a geochemical match, but we didn't have the age of the Shala eruption," said Vidal. "I immediately sent the samples of Shala volcano to our colleagues in Glasgow so they could measure the age of the rocks. When I received the results and found out that the oldest Homo sapiens from the region was older than previously assumed, I was really excited."
"The Omo Kibish Formation is an extensive sedimentary deposit which has been barely accessed and investigated in the past," said co-author and co-leader of the field investigation Professor Asfawossen Asrat from Addis Ababa University in Ethiopia, who is currently at BIUST in Botswana. "Our closer look into the stratigraphy of the Omo Kibish Formation, particularly the ash layers, allowed us to push the age of the oldest Homo sapiens in the region to at least 230,000 years."
"Unlike other Middle Pleistocene fossils which are thought to belong to the early stages of the Homo sapiens lineage, Omo I possesses unequivocal modern human characteristics, such as a tall and globular cranial vault and a chin," said co-author Dr. Aurélien Mounier from the Musée de l'Homme in Paris. "The new date estimate, de facto, makes it the oldest unchallenged Homo sapiens in Africa."
The researchers say that while this study shows a new minimum age for Homo sapiens in eastern Africa, it's possible that new finds and new studies may extend the age of our species even further back in time.
"We can only date humanity based on the fossils that we have, so it's impossible to say that this is the definitive age of our species," said Vidal. "The study of human evolution is always in motion: boundaries and timelines change as our understanding improves. But these fossils show just how resilient humans are: that we survived, thrived and migrated in an area that was so prone to natural disasters."
"It's probably no coincidence that our earliest ancestors lived in such a geologically active rift valley—it collected rainfall in lakes, providing fresh water and attracting animals, and served as a natural migration corridor stretching thousands of kilometers," said Oppenheimer. "The volcanoes provided fantastic materials to make stone tools and from time to time we had to develop our cognitive skills when large eruptions transformed the landscape."
"Our forensic approach provides a new minimum age for Homo sapiens in eastern Africa, but the challenge still remains to provide a cap, a maximum age, for their emergence, which is widely believed to have taken place in this region," said co-author Professor Christine Lane, head of the Cambridge Tephra Laboratory where much of the work was carried out. "It's possible that new finds and new studies may extend the age of our species even further back in time."
"There are many other ash layers we are trying to correlate with eruptions of the Ethiopian Rift and ash deposits from other sedimentary formations," said Vidal. "In time, we hope to better constrain the age of other fossils in the region."
"Early humans gained energy budget by increasing rate of energy acquisition, not energy-saving adaptation"
A team of researchers affiliated with multiple institutions in the U.S., the Institute for Advanced Study in Toulouse, France and the Max Planck Institute for Evolutionary Anthropology in Germany has found evidence that suggests early humans gained an energy budget by increasing their rate of energy acquisition, not by taking advantage of adaptive strategies. In their paper published in the journal Science, they describe their study of energy expenditure versus energy intake in early humans.
In this new effort, the researchers noted that humans long ago diverged in significant ways from the other great apes. They wondered how this happened and decided to look at energy intake and expenditure. People and other animals have to put in a certain amount of work (expenditure) to receive an energy intake. Climbing a tree to fetch a banana is a simple example. The amount of energy required to climb a tree far outweighs the potential benefit of eating a single banana. But if a single person is able to throw down multiple bananas, then the overall energy intake may surpass the effort of climbing a tree a single time. To learn more about how energy intake and expenditure might have led to modern human characteristics, the researchers studied two groups of modern people—hunter gatherers in Tanzania and forager-horticulturalists in a Bolivian rain forest.
In looking at both groups, they found that both spent more energy on subsistence but also achieved energy efficiencies compared to modern great apes. This was despite the fact that bipedalism and the use of tools are known to decrease the amount of energy expended to obtain food. The result was the acquisition of more food at a much higher rate than the great apes. The researchers suggest this indicates that humans are not cost economizers but are instead creatures that operate in high throughput ways that lead to large payoffs. They suggest that diverging from the great apes in such a way led to the production of so much food that early humans had much more time to do other things, such as socialize. They further suggest that such socializing, combined with the organizational activities involved in obtaining food led to the development of larger brains and from there, other uniquely human attributes.
"Woolly mammoths survived on mainland North America until 5,000 years ago, DNA reveals"
Woolly mammoths may have survived in North America thousands of years longer than scientists previously thought, vials of Alaskan permafrost reveal.
The hairy beasts might have persisted in what is now the Yukon, in Canada, until around 5,000 years ago — 5,000 years longer than experts previously estimated, a new study suggests. That conclusion comes from snippets of mammoth DNA that were found in vials of frozen dirt that had been stored and forgotten in a laboratory freezer for a decade.
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"Organisms are constantly shedding cells throughout their life," said study lead author Tyler Murchie, a postdoctoral researcher in the Department of Anthropology at McMaster University in Ontario. For instance, He explained thata person sheds roughly 40,000 skin cells per hour, on average, meaning we are constantly ejecting bits of our DNA into our surroundings.
That's also true of other life-forms; nonhuman animals, plants, fungi, and microbes are constantly leaving microscopic breadcrumb trails everywhere. Most of this genetic detritus doesn't linger in the environment, though. Soon after being discarded, the vast majority of the DNA bits are consumed by microbes, Murchie said. The fraction of the shed DNA that does remain might bind to a small bit of mineral sediment and be preserved. Though only a tiny proportion of what was initially shed remains centuries later, it can nevertheless provide a window into a vanished world teeming with strange creatures.
"In a tiny fleck of dirt," Murchie told Live Science, "is DNA from full ecosystems."
Murchie analyzed soil samples taken from permafrost in the central Yukon. Many of the samples dated to the Pleistocene-Holocene transition (14,000-11,000 years ago), a period marked by rapidly changingclimatic conditions in which many large mammals — such as saber-toothedicats, mammoths and mastodons — vanished from the fossil record.
The DNA fragments in Murchie's samples were small — often no larger than 50 letters, or base pairs. However, on average, he was able to isolate roughly 2 million DNA fragments per sample. By analyzing DNA from soil samples of known ages, he indirectly observed the evolution of ancient ecosystems over this turbulent period.
Soil collection in the Yukon
Researchers collect permafrost in the Yukon. (Image credit: Photo by Tyler Murchie)
The main advantage to studying ancient DNA is that researchers can observe organisms that tended not to fossilize well. "An animal has only one body," said Murchie, and the odds of it fossilizing are not that great. On top of that, you have to find it. But that same animal constantly ejected innumerable amounts of DNA into the environment throughout its lifetime.
The soil samples — which span a period of time from 30,000 years ago to 5,000 years ago — revealed that mammoths and horses likely persisted in this Arctic environment much longer than previously thought. Mammoths and horses were in steep decline by the Pleistocene-Holocene transition, the DNA data suggest, but they didn't disappear all at once due to changes in climate or overhunting.
An earlier study, published in October in the journal Nature, suggested that some mammoths survived on isolated islands away from human contact until 4,000 years ago. However, the new study is the first to determine that small populations of mammoths coexisted with humans on the mainland of North America well into the Holocene, as recently as 5,000 years ago.
. Megafauna extinctions from this era have largely been blamed on one of two explanations: human paleo-hunters or climate catastrophe, said lead author Hendrik Poinar, an evolutionary geneticist and director of the McMaster Ancient DNA Centre.
However, the new study "changes the focus away from this two-pitted debate that has plagued [paleontology] for so long," Poinar said.
The team's research provides evidence that the extinction of North American megafauna is much more nuanced, he said. There's no doubt that the animals were under pressure from both human hunters and a rapidly changing climate. The question is, "how much were they hunted and whether or not that was truly the tipping point," Poinar told Live Science.
Analyzing ancient DNA from dirt has the potential to tell us a lot about ancient life; Poinar and Murchie said Arctic permafrost is ideal for these types of ancient DNA studies because freezing preserves ancient DNA very well. But that might not be possible forever: As ice in the Arctic melts due to rapid increases in temperature, "we're going to lose a lot of that life history data," Murchie said. "It's just going to fall away before anyone gets a chance to study it."
"Weird structures near Earth's core may be scars from a primordial interplanetary collision"
A group of mysterious, ultradense structures just outside Earth's core may be the remnants of an ancient interplanetary collision, new research suggests.
These strange structures are known as ultralow-velocity zones (ULVZs), because seismic waves generated by earthquakes travel about 50% more slowly through these zones than through the surrounding mantle. That means the ULVZs are also much denser than the rest of the mantle, and possibly made of heavier elements.
It's hard to say anything for certain about these dense blobs of rock, because the ULVZs sit nearly 1,800 miles (2,900 kilometers) below Earth's surface — one group clustered deep below Africa, and another below the Pacific Ocean, where the rocky mantle and liquid-metal outer core meet. That's far too deep for human eyes to see; only seismic data can offer clues about the size, shape and structure of the ULVZs.
Now, using a new computer model and fresh seismic observations from deep below Australia and New Zealand, researchers may have added an important piece to the ULVZ puzzle. According to a study published Dec. 30, 2021, in the journal Nature Geoscience, these zones aren't uniform structures but rather seem to be made of layers of different materials that accumulated over the eons.
"The most surprising finding is that the ultra-low velocity zones are not homogenous but contain strong structural and compositional variations within them," lead study author Surya Pachhai, a postdoctoral scholar at the Australian National University, said in a statement. "This type of ULVZ can be explained by chemical [variations] created at the very beginning of the Earth's history, which are still not well mixed after 4.5 billion years of mantle convection."
(Mantle convection is the process by which the solid rocks in the planet’s mantle slowly move in accordance with heat currents.)
After their computer simulations showed that a layered or mixed structure was likely within the ULVZs, the researchers suggested a possible origin story for the structures — a story that starts more than 4 billion years ago, around the time early Earth's rocky crust first formed. Beneath the surface, heavier elements, like iron, were sinking toward the planet's core, while lighter elements, like silicon, rose toward the mantle.
This organization all went haywire when a Mars-size planet known as Theia slammed directly into the early Earth — an ancient cataclysm that researchers call the giant impact hypothesis. The collision may have scattered enormous amounts of debris into Earth's orbit — possibly leading to the formation of the moon — while also raising the entire planet's temperature and creating a large "ocean" of magma on the planet's surface, Pachhai said.
Various rocks, gases and crystals forged during the collision would have been scattered through this magma ocean, the researchers said — but not forever. Over the following billions of years, heavier materials would have sunk toward the bottom of the mantle, followed by lighter ones — eventually creating a densely layered structure of iron and other elements at the core-mantle boundary. As the mantle churned over the ages, this dense layer would have separated into smaller clumps spread across the lower mantle — effectively giving us the ULVZs we know of today.
This scenario may not explain the source of all ULVZs, the researchers added, as there is also some evidence that other phenomena — such as melting ocean crust sinking into the mantle — could explain ULVZs. However, the team's models show that the giant impact hypothesis reliably explains how the dense, layered zones could have been created.
"A supernova blast may have caused a mass extinction 359 million years ago"
About 359 million years ago, at the end of the last phase of the Devonian period, there was a mass extinction event or series of events. An estimated 70 to 80 percent of the creatures living in the Earth’s coral reefs during the so-called “age of fish” were wiped out.
There are theories about what happened, from volcanic activity, to predatory plants run amuck (!), to an asteroid impact similar to the one believed to have killed off the planet’s large dinosaurs, but no clear cause has been confirmed.
A study published in the Proceedings of the National Academy of Sciences from the University of Illinois Urbana-Champaign published in August proposes a more distant trigger: A supernova 65 light-years away in space destroyed the Earth’s ozone layer.
The researchers say that a supernova would be capable of damaging the ozone layer for as long as 100,000 years.
In the same way that humankind has learned over the past century that events in one place often affect another, says lead study author astrophysicist Brian Fields:
“The overarching message of our study is that life on Earth does not exist in isolation. We are citizens of a larger cosmos, and the cosmos intervenes in our lives — often imperceptibly, but sometimes ferociously.”
Fields and his colleagues arrived at their conclusion as they sought to explain an abundance of sunburnt plant spores, thousands of generations of them, located at the geologic boundary between the Devonian and Carboniferous periods. To the researchers, they indicate an extended period of ozone depletion in the Earth’s atmosphere. (While terrestrial plants and insects weren’t as decimated as sea organisms during the extinction, they were nonetheless subjected to whatever it was that happened.)
Fields says there’s scant evidence of a local culprit such as volcanic activity. His team also ruled out dramatic events such as meteorites, solar storms, or gamma-ray bursts. As grad student co-author Jesse Miller explains, “These events end quickly and are unlikely to cause the long-lasting ozone depletion that happened at the end of the Devonian period.”
“Instead,” says Fields, “we propose that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the protracted loss of ozone.”
Such a flash of light would be both spectacular to witness and deadly. The researchers say that a supernova would be capable of damaging the ozone layer for as long as 100,000 years. Such an event would constitute a “one-two punch.” It would begin with a barrage of destructive ultraviolet rays, X-rays, and gamma rays. This would be followed by a longer-term increase in cosmic rays striking the Earth as a result of blast debris colliding with surrounding gases and driving increased particle acceleration.
Considering that there was apparently a 300,000-year decline in biodiversity before the massive die-off, the team suggests that the Earth may even have been affected by a series of supernova explosions instead of just one.
“This is entirely possible,” says Miller. “Massive stars usually occur in clusters with other massive stars, and other supernovae are likely to occur soon after the first explosion.”
A “smoking gun” for the supernova hypothesis
The only way to verify the theory put forth by Fields’ team would be to find a particular pair of radioactive isotopes—plutonium-244 and samarium-146—in the geologic record for the time frame in question.
Undergraduate co-author Zhenghai Liu explains, “Neither of these isotopes occurs naturally on Earth today, and the only way they can get here is via cosmic explosions.”
Fields compares locating such isotopes to finding green bananas: “When you see green bananas in Illinois, you know they are fresh, and you know they did not grow here. Like bananas, Pu-244 and Sm-146 decay over time. So if we find these radioisotopes on Earth today, we know they are fresh and not from here—the green bananas of the isotope world—and thus the smoking guns of a nearby supernova.”
The search for the isotopes has yet to begin.
Meanwhile, there’s little reason to worry about future supernovae doing to us what those earlier ones may have done to the Earth’s coral reefs, science fiction notwithstanding. Says another co-author, grad student Adrienne Ertel, “To put this into perspective, one of the closest supernova threats today is from the star Betelgeuse, which is over 600 light-years away.”
"Little Foot’s shoulders hint at how a human-chimp common ancestor climbed"
Extraits de l'article:
Little Foot, a nearly complete hominid skeleton painstakingly excavated from rock inside a South African cave, shouldered a powerful evolutionary load.
This 3.67-million-year-old adult female sports the oldest and most complete set of shoulder blades and collarbones of any ancient hominid. Those fossils also provide the best available model for what the shoulders of the last common ancestor of humans and chimpanzees looked like, say Kristian Carlson, a paleoanthropologist at the University of Southern California in Los Angeles, and his colleagues. Their results provide new insights into how both Little Foot and a human-chimp last common ancestor climbed in trees.
Little Foot belonged to the Australopithecus genus, but her species identity is in dispute (SN: 12/12/18). The shape and orientation of her shoulder bones fall between corresponding measures for humans and present-day African apes, but most closely align with gorillas, Carlson reported April 27 at the virtual annual meeting of the American Association of Physical Anthropologists. His talk was based on a paper published online April 20 in the Journal of Human Evolution.
Little Foot lived roughly half-way between modern times and the estimated age of a human-chimp common ancestor, says paleobiologist David Green of Campbell University in Buies Creek, N.C., a member of Carlson’s team. If that ancient ancestral creature was about the size of a chimp, as many researchers suspect, shoulders resembling those of gorillas would have supported slow but competent climbing, Green says. Gorillas spend much of the time knuckle-walking on the ground. These apes climb trees with all four limbs, reaching up with powerful shoulders and arms to pull themselves along.
“The maintenance of a gorilla-like shoulder in Little Foot offers clues that climbing remained vital for early [hominids],” Green says. It’s possible, he added, that Little Foot’s shoulder design represented “evolutionary baggage” among hominids evolving bodies more suited to upright walking.
Researchers used a digital reconstruction of Little Foot’s nearly complete right shoulder blade, shown here, to determine that this ancient hominid climbed more like gorillas than like chimps, orangutans or humans.
The new analysis makes Little Foot’s shoulders “our best candidate for hypothesizing the appearance of the human-chimp last common ancestor,” says anatomist Susan Larson of Stony Brook University School of Medicine in New York, who wasn’t involved in the research. Ancestral shoulders that supported capable tree climbing would have provided a foundation for the evolution of human shoulders aligned with a two-legged stride and chimp shoulders designed for hanging and swinging from tree branches, she suggested.
In the new study, a digital, 3-D reconstruction of Little Foot’s more complete right shoulder blade was compared with right shoulder blades of chimps, gorillas, orangutans and present-day people. Further comparisons were made with partial shoulder blades of 11 ancient hominids. Those hominids included four South African Australopithecus specimens and East African finds from two members of Lucy’s species, A. afarensis, that date to around 3.3 million and 3.6 million years ago (SN: 10/25/12). Little Foot’s collarbones were compared with those of humans, chimps, gorillas, orangutans and seven ancient hominids.
Carlson’s analysis provides preliminary but still uncertain evidence that Little Foot had the most gorilla-like shoulders of any ancient hominid, says paleoanthropologist Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Melillo, who did not participate in the new study, considers it most striking that Little Foot shares many shoulder similarities with the other Australopithecus fossils studied by Carlson’s team.
Some researchers consider a 4.4-million-year-old Ardipithecus ramidus skeleton, dubbed Ardi, the best hominid model for a human-chimp last common ancestor (SN: 12/31/09). Ardi could have moved slowly in trees while holding onto branches above her head, in a manner unlike any modern ape, they contend. But Ardi’s remains lack shoulder blades and collarbones.
"Our ancestors first developed humanlike brains 1.7 million years ago"
For nearly two centuries, scientists have known that humans descended from the great apes. But it’s proven difficult to precisely map out the branches of that evolutionary tree, especially in terms of determining when and where early Homo species first developed brains similar to modern humans.
There are clear differences between ape and human brains. Compared to apes, the Homo sapiens brain is larger, and its frontal lobe is organized such that we can engage in toolmaking, planning, and language. Other Homo species also enjoyed some of these cognitive innovations, from the Neanderthals to Homo floresiensis, the hobbit-like people who once inhabited Indonesia.
One reason it’s been difficult to discern the details of this cognitive evolution from apes to Homo species is that brains don’t fossilize, so scientists can’t directly study early primate brains. But primate skulls offer clues.
Brains of yore
In a new study published in Science, an international team of researchers analyzed impressions left on the skulls of Homo species to better understand the evolution of primate brains. Using computer tomography on fossil skulls, the team generated images of what the brain structures of early Homo species probably looked like, and then compared those structures to the brains of great apes and modern humans.
The results suggest that Homo species first developed humanlike brains approximately 1.7 to 1.5 million years ago in Africa. This cognitive evolution occurred at roughly the same time Homo species’ technology and culture were becoming more complex, with these species developing more sophisticated stone tools and animal food resources.
The team hypothesized that “this pattern reflects interdependent processes of brain-culture coevolution, where cultural innovation triggered changes in cortical interconnectivity and ultimately in external frontal lobe topography.”
The team also found that these structural changes occurred after Homo species migrated out of Africa for regions like modern-day Georgia and Southeast Asia, which is where the fossils in the study were discovered. In other words, Homo species still had ape-like brains when some groups first left Africa.
While the study sheds new light on the evolution of primate brains, the team said there’s still much to learn about the history of early Homo species, particularly in terms of explaining the morphological diversity of Homo fossils discovered in Africa.
“Deciphering evolutionary process in early Homo remains a challenge that will be met only through the recovery of expanded fossil samples from well-controlled chronological contexts,” the researchers wrote.
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