The footprints originate from a group of people of various ages. Credit: National Park Service
New research, supported by innovative dating techniques, suggests that humans settled in the Americas around 23,000 years back, challenging earlier beliefs of a 14,000-year timeline.
When and how human beings very first settled in the Americas is a topic of significant debate. In the 20th century, archaeologists believed that humans reached the North American interior no earlier than around 14,000 years back.
However our new research study discovered something various. Our most current research study supports the view that people remained in America about 23,000 years earlier.
Ice-Free Corridor and Previous Assumptions
The 20th-century specialists thought the appearance of humans had actually corresponded with the formation of an ice-free passage between 2 tremendous ice sheets straddling whats now Canada and the northern United States. According to this idea, the passage, triggered by melting at the end of the last Ice Age, enabled people to trek from Alaska into the heart of North America.
Slowly, this orthodoxy fallen apart. In recent years, dates for the earliest evidence of people have crept back from 14,000 years ago to 16,000 years back. This is still consistent with people only reaching the Americas as the last Ice Age was ending.
In September 2021, we released a paper in Science that dated fossil footprints revealed in New Mexico to around 23,000 years back– the height of the last Ice Age. They were made by a group of individuals passing by an ancient lake near whats now White Sands. The discovery included 7,000 years to the record of human beings on the continent, rewriting American prehistory.
If people were in America at the height of the last Ice Age, either the ice posed couple of barriers to their passage, or human beings had actually been there for a lot longer. Maybe they had actually reached the continent during an earlier duration of melting.
Our conclusions were slammed, however, we have actually now released evidence confirming the early dates.
Pollen can be a useful tool for dating evidence of human settlement.
Dating the Footprints and the Pollen Mystery
For lots of people, the word pollen creates a summer of allergies, sneezing, and anguish. But fossilized pollen can be a powerful scientific tool.
In our 2021 study, we performed radiocarbon dating on typical ditch yard seeds discovered in sediment layers above and listed below where the footprints were found. Radiocarbon dating is based on how a specific type– called an isotope– of carbon (carbon-14) undergoes radioactive decay in organisms that have actually died within the last 50,000 years.
Some scientists claimed that the radiocarbon dates in our 2021 research were too old because they went through something called the “tough water” effect. Water consists of carbonate salts and for that reason carbon. Difficult water is groundwater that has been separated from the environment for some duration of time, implying that some of its carbon-14 has actually currently undergone radioactive decay.
Typical ditch grass is an aquatic plant and the critics said seeds from this plant could have taken in old water, rushing the dates in a way that made them appear older than they were.
Its quite right that they raised this problem. This is the method that science must continue, with claim and counter-claim.
The Role of Advanced Technology and Conclusive Findings
Radiocarbon dating is robust and well-understood. Two members of our team, Kathleen Springer and Jeff Pigati of the United States Geological Survey set out to date the pollen grains.
This posed a powerful challenge: you need thousands of them to get sufficient carbon to date something. In fact, you need 70,000 grains or more.
Medical science supplied an amazing option to our problem. We used a technique called circulation cytometry, which is more typically utilized for counting and sampling private human cells, to count and separate fossil pollen for radiocarbon dating.
Circulation cytometry uses the fluorescent residential or commercial properties of cells, promoted by a laser. These cells move through a stream of liquid. Fluorescence causes a gate to open, allowing specific cells in the circulation of liquid to be diverted, tested, and focused.
We have pollen grains in all sediment layers between the footprints at White Sands, which allows us to date them. The key benefit of having a lot pollen is that you can choose plants like evergreen that are not affected by old water. Our samples were processed to concentrate the pollen within them using circulation cytometry.
After a year or more of costly and labor-intensive laboratory work, we were rewarded with dates based upon pine pollen that confirmed the original chronology of the footprints. They also revealed that old water impacts were absent at this website.
When people made the footprints, the pollen also permitted us to rebuild greenery that was growing. We got exactly the sort of plants we would expect to have been there during the Ice Age in New Mexico.
We likewise used a various dating strategy called optically promoted luminescence (OSL) as an independent check. OSL counts on the build-up of energy within buried grains of quartz with time. This energy originates from the background radiation thats all around us.
The more energy we discover, 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 eliminate them thoroughly to prevent exposing them to light. Taking quartz grains from the center of television, you expose them to light in the laboratory and measure the light discharged by grains. This reveals their age. The dates from OSL supported those we got utilizing other methods.
The humble pollen grain and some magnificent medical innovation assisted us verify the dates the footprints were made, and when individuals reached the Americas.
For more on this story, see Ancient Footprints in New Mexico Changes Timeline for Early Human Presence in North America.
Written by:
Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University
Sally Christine Reynolds, Associate Professor in Hominin Palaeoecology, Bournemouth University
Adjusted from an article originally released in The Conversation.
In current years, dates for the earliest proof of people have crept back from 14,000 years ago to 16,000 years earlier. In September 2021, we released a paper in Science that dated fossil footprints uncovered in New Mexico to around 23,000 years earlier– the height of the last Ice Age. Two members of our group, Kathleen Springer and Jeff Pigati of the United States Geological Survey set out to date the pollen grains. We have pollen grains in all sediment layers between the footprints at White Sands, which enables us to date them. We likewise utilized a different dating strategy called optically stimulated luminescence (OSL) as an independent check.