Tagged / footprints

Conversation article: Humans got to America 7,000 years earlier than thought, new research confirms

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Professor Matthew Bennett and Dr Sally Reynolds write for The Conversation about their research dating fossil footprints found in New Mexico…

Humans got to America 7,000 years earlier than thought, new research confirms

The footprints come from a group of people of different ages.
National Park Service

Matthew Robert Bennett, Bournemouth University and Sally Christine Reynolds, Bournemouth University

When and how humans first settled in the Americas is a subject of considerable controversy. In the 20th century, archaeologists believed that humans reached the North American interior no earlier than around 14,000 years ago.

But our new research found something different. Our latest study supports the view that people were in America about 23,000 years ago.

The 20th century experts thought the appearance of humans had coincided with the formation of an ice-free corridor between two immense ice sheets straddling what’s now Canada and the northern US. According to this idea, the corridor, caused by melting at the end of the last Ice Age, allowed humans to trek from Alaska into the heart of North America.

Gradually, this orthodoxy crumbled. In recent decades, dates for the earliest evidence of people have crept back from 14,000 years ago to 16,000 years ago. This is still consistent with humans only reaching the Americas as the last Ice Age was ending.

In September 2021, we published a paper in Science that dated fossil footprints uncovered in New Mexico to around 23,000 years ago – the height of the last Ice Age. They were made by a group of people passing by an ancient lake near what’s now White Sands. The discovery added 7,000 years to the record of humans on the continent, rewriting American prehistory.

If humans were in America at the height of the last Ice Age, either the ice posed few barriers to their passage, or humans had been there for much longer. Perhaps they had reached the continent during an earlier period of melting.

Our conclusions were criticised, however we have now published evidence confirming the early dates.

Dating the pollen

For many people, the word pollen conjures up a summer of allergies, sneezing and misery. But fossilised pollen can be a powerful scientific tool.

In our 2021 study, we carried out radiocarbon dating on common ditch grass seeds found in sediment layers above and below where the footprints were found. Radiocarbon dating is based on how a particular form – called an isotope – of carbon (carbon-14) undergoes radioactive decay in organisms that have died within the last 50,000 years.

Some researchers claimed that the radiocarbon dates in our 2021 research were too old because they were subject to something called the “hard water” effect. Water contains carbonate salts and therefore carbon. Hard water is groundwater that has been isolated from the atmosphere for some period of time, meaning that some of its carbon-14 has already undergone radioactive decay.

Common ditch grass is an aquatic plant and the critics said seeds from this plant could have consumed old water, scrambling the dates in a way that made them seem older than they were.

It’s quite right that they raised this issue. This is the way that science should proceed, with claim and counter-claim.

How did we test our claim?

Radiocarbon dating is robust and well understood. You can date any type of organic matter in this way as long as you have enough of it. So two members of our team, Kathleen Springer and Jeff Pigati of the United States Geological Survey set out to date the pollen grains. However, pollen grains are really small, typically about 0.005 millimetres in diameter, so you need lots of them.

This posed a formidable challenge: you need thousands of them to get enough carbon to date something. In fact, you need 70,000 grains or more.

Medical science provided a remarkable solution to our conundrum. We used a technique called flow cytometry, which is more commonly used for counting and sampling individual human cells, to count and isolate fossil pollen for radiocarbon dating.

Flow cytometry uses the fluorescent properties of cells, stimulated by a laser. These cells move through a stream of liquid. Fluorescence causes a gate to open, allowing individual cells in the flow of liquid to be diverted, sampled, and concentrated.

Illustration of pollen grains.
Pollen can be a useful tool for dating evidence of human settlement.
Kateryna Kon / Shutterstock

We have pollen grains in all sediment layers between the footprints at White Sands, which allows us to date them. The key advantage of having so much pollen is that you can pick plants like pine trees that are not affected by old water. Our samples were processed to concentrate the pollen within them using flow cytometry.

After a year or more of labour intensive and expensive laboratory work, we were rewarded with dates based on pine pollen that validated the original chronology of the footprints. They also showed that old water effects were absent at this site.

The pollen also allowed us to reconstruct vegetation that was growing when people made the footprints. We got exactly the kinds of plants we would expect to have been there during the Ice Age in New Mexico.

We also used a different dating technique called optically stimulated luminescence (OSL) as an independent check. OSL relies on the accumulation of energy within buried grains of quartz over time. This energy comes from the background radiation that’s all around us.

The more energy we find, the older we can assume the quartz grains are. This energy is released when the quartz is exposed to light, so what you are dating is the last time the quartz grains saw sunlight.

To sample the buried quartz, you drive metal tubes into the sediment and remove them carefully to avoid exposing them to light. Taking quartz grains from the centre of the tube, you expose them to light in the lab and measure the light emitted by grains. This reveals their age. The dates from OSL supported those we got using other techniques.

The humble pollen grain and some marvellous medical technology helped us confirm the dates the footprints were made, and when people reached the Americas.The Conversation

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Associate Professor in Hominin Palaeoecology, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Conversation article: A new species of early human? Why we should be cautious about new fossil footprint findings

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Writing for The Conversation, Professor Matthew Bennett and Dr Sally Reynolds discuss the potential discovery of an early human species…

A new species of early human? Why we should be cautious about new fossil footprint findings

Dawid A. Iurino for THOR, Author provided

Matthew Robert Bennett, Bournemouth University and Sally Christine Reynolds, Bournemouth University

A collection of fossil footprints at Laetoli in Northern Tanzania, preserved in volcanic ash and dated to 3.66 million years ago, are still yielding surprises almost 45 years after their discovery.

Based on a re-analysis of fossil footprints from one of Laetoli’s sites, the authors of a new study published in the journal Nature say they’ve discovered evidence of a previously unknown early human species at this spot. However, there are reasons to be cautious about this conclusion.

Before we delve into these new findings, let’s orientate ourselves. Laetoli, an area well-known for paleontological excavations, has a number of distinct sites, each denoted by letters of the alphabet. British paleoanthropolgist Mary Leakey and her colleagues first reported fossil footprints in 1978 at Site G, the main track site at Laetoli.

In 2016, a team led by Fidelis Masao, an archaeologist in Tanzania, uncovered additional tracks close to Site G, at Site S. The footprints from Sites G and S are usually assigned to the well-known ancestral human (hominin) species Australopithecus afarensis, of which the skeleton “Lucy” is the best-known example.

Less well-known is the fact that in 1976, two years before Leakey’s famous discovery, a set of five footprints were found at Site A. Importantly, all these sites occur on the same ash surface, so we know they date from the same time period.

But the five footprints from Site A were largely forgotten, eclipsed by Leakey’s later discovery. This was understandable because the footprints at Site A had poor morphological shape, or definition, and there were fewer of them (there are more than 30 individual footprints at Site G).

In 1987, American paleoanthropologist Russell Tuttle suggested that these footprints may have been made by a species of bear, or by a different hominin from those of Site G. He also cautioned that the diversity in the footprints’ form as compared to those at Site G might simply reflect the changing properties of the ash layer over which the hominin walked.

Seeking to find out who these footprints belonged to, a team of international researchers re-excavated the tracks from Site A in 2019. Their findings are the focus of the new paper in Nature.

The researchers used various methods including photography and 3D scanning to inspect the Site A footprints. They compared the width and length with footprints from black bears, chimpanzees and humans, as well as the tracks from Sites G and S. They also explored the bear hypothesis by examining video footage of modern black bears which, on rare occasions, walk upright.

The authors concluded that on balance, the footprints at Site A did not resemble bear tracks, and were different from the footprints at Sites G and S.

One particular feature they draw attention to is that the Site A trackway cross-steps, almost as if one was attempting to toe a line as part of sobriety test. Based on this and their other findings, the authors suggest that the tracks at Site A were made by a different hominin than those at sites G and S. They argue that two hominin species walked the Laetoli landscape 3.66 million years ago.

A footprint from Site A on the left and Site G on the right.
Image on left by Jeremy DeSilva and on right by Eli Burakian/Dartmouth.

The broader evolutionary context at this time suggests what the authors are proposing would be possible. There was more than one species of hominin on the African landscape during this period, and we’ve seen anatomical variation in the foot within some Australopithecus species. That said, it’s quite a significant leap to identify a second species based on a handful of poorly defined tracks.

Variation in trackways is the key issue here. Imagine going for a walk down a beach or sandy path. The footprints you make will vary from one step to the next. This reflects natural variability in human gait, as well as subtle differences in the characteristics of the ground you’re walking on.

In a recent paper we suggested that you need a minimum of between ten and 20 footprints before you can confidently quantify the variability in just one dimension, such as footprint length, let alone several. Others have suggested that you may need over 250 tracks to adequately quantify the three-dimensional form of a footprint.

Footfall and the resulting footprints are more variable than once thought and some have argued that even individuals of the same species may have highly unique gaits.

In this context it is rather surprising that the authors of this paper make inferences not just about one individual, but a whole species.

One way to strengthen their conclusions would be to use modern “whole foot” methods to statistically compare the best footprint at Site A with those at Sites S and G. This could be an approach for future research.

Certainly more evidence is needed to determine whether these footprints justify this excitement, and do indeed belong to another early human species.The Conversation

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Principal Academic in Hominin Palaeoecology, Bournemouth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

What ancient footprints can tell us about what it was like to be a child in prehistoric times

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File 20180212 58327 vep4i.jpg?ixlib=rb 1.1

Footprint from 700,000 years ago. Matthew Bennett, Author provided

By Professor Matthew Bennett and Dr Sally Reynolds.

Western society has a rather specific view of what a good childhood should be like; protecting, sheltering and legislating to ensure compliance with it. However, perceptions of childhood vary greatly with geography, culture and time. What was it like to be a child in prehistoric times, for example – in the absence of toys, tablets and television?

In our new paper, published in Scientific Reports, we outline the discovery of children’s footprints in Ethiopia which show how children spent their time 700,000 years ago.

We first came across the question of what footprints can tell us about past childhood experiences a few years back while studying some astonishingly beautiful children’s footprints in Namibia, just south of Walvis Bay. In archaeological terms the tracks were young, dating only from around 1,500 years ago. They were made by a small group of children walking across a drying mud surface after a flock of sheep or goats. Some of these tracks were made by children as young as three-years-old in the company of slightly older children and perhaps young adolescents.

Namibian footprints. Matthew Bennett, Author provided

The detail in these tracks, preserved beneath the shifting sands of the Namibian Sand Sea, is amazing, and the pattern of footfall – with the occasional skip, hop and jump – shows they were being playful. The site also showed that children were trusted with the family flock of animals from an early age and, one assumes, they learnt from that experience how to function as adults were expected to within that culture.

No helicopter parents

But what about the childhood of our earlier ancestors – those that came before anatomically modern humans (Homo sapiens)? Children’s tracks by Homo antecessor (1.2m to 800,000 years ago) were found at Happisburgh in East Anglia, a site dating to a million years ago. Sadly though, these tracks leave no insight into what these children were doing.

Reconstruction of Homo Heidelbergensis. Jose Luis Martinez Alvarez/wikipedia, CC BY-SA

But the footprints described in our recent study – from a remarkable site in the Upper Awash Valley of Southern Ethiopia that was excavated by researchers from the Università di Roma “La Sapienza” – reveal a bit more. The children’s tracks were probably made by the extinct species Homo heidelbergensis(600,000 to 200,000 years ago), occurring next to adult prints and an abundance of animal tracks congregated around a small, muddy pool. Stone tools and the butchered remains of a hippo were also found at the site, called Melka Kunture.

This assemblage of tracks is capped by an ash flow from a nearby volcano which has been dated to 700,000 years ago. The ash flow was deposited shortly after the tracks were left, although we don’t know precisely how soon after. The tracks are not as anatomically distinct as those from Namibia but they are smaller and may have been made by children as young as one or two, standing in the mud while their parents and older siblings got on with their activities. This included knapping the stone tools with which they butchered the carcass of the hippo.

The findings create a unique and momentary insight into the world of a child long ago. They clearly were not left at home with a babysitter when the parents were hunting. In the harsh savannah plains of the East African Rift Valley, it was natural to bring your children to such daily tasks, perhaps so they could observe and learn.

This is not surprising, when one considers the wealth of ethnographic evidence from modern, culturally distinct human societies. Babies and children are most often seen as the lowliest members of their social and family groups. They are often expected to contribute to activities that support the mother, and the wider family group, according to their abilities. In many societies, small boys tend to help with herding, while young girls are preferred as babysitters. Interestingly, adult tools – like axes, knives, machetes, even guns – are often freely available to children as a way of learning.

Artistic impression of scene at Melka Kunture. Matthew Bennett, Author provided

So, if we picture the scene at Melka Kunture, the children observing the butchery were probably allowed to handle stone tools and practice their skills on discarded pieces of carcass while staying out of the way of the fully-occupied adults. This was their school room, and the curriculum was the acquisition of survival skills. There was little time or space to simply be a child, in the sense that we would recognise today.

This was likely the case for a very long time. The Monte Hermoso Human Footprint Site in Argentina (roughly 7,000-years-old) contains predominantly small tracks (of children and women) preserved in coastal sediments and it has been suggested that the children may have played an important role in gathering seafood or coastal resources. Similarly, most of the tracks in the Tuc d’Audoubert Cave in France (15,000-years-old) are those of children and the art there is striking. Perhaps they were present when it was carved and painted?

However, these observations contrasts to the story that emerged last year based on tracks from the older Homo Homo erectus (1.5m-year-old) at Ileret, located further south in the Rift Valley, just within the northern border of Kenya. Here the tracks have been interpreted as the product of adult hunting groups moving along a lake shore, rather than a domestic scene such as that at Melka Kunture. However, these scenes aren’t mutually exclusive and both show the power of footprints to provide a snapshot into past hominin behaviour.

But it does seem like the overwhelming parenting lesson from the distant past is that children had more responsibilities, less adult supervision and certainly no indulgence from their parents. It is a picture of a childhood very different from our own, at least from the privileged perspective of life in Western society.

 

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Sally Christine Reynolds, Senior Lecturer in Hominin Palaeoecology, Bournemouth University

This article was originally published on The Conversation. Read the original article.