The first people in North America may have arrived more than 100,000 years earlier than scientists have believed.

There should not have been any humans the Americas until about 30,000 years ago. But now scientists have found conflicting evidence of a much older human presence in an animal skeleton.

Researchers analyzed the skeleton of a so-called mastodon – a relative of today’s elephants – found 1992 in California. The skeleton marks indicate that the mastodon may have been killed by people, who would have reached North America 100,000 years earlier than previously thought.

The team of researcher updated previous age estimates using the more precise method of uranium-thorium, which measures the radioactive decomposition of uranium isotopes to thorium. A method considered reliable for estimation within this window in time.

The mastodon legs show clear signs of having been broken by man-made tools, perhaps to gain access to the bone marrow within. The researchers also found different types of stones at the excavation site around the skeleton, which may have been used as tools to process the mastodon.

Using leg bone used from an elephant that had recently died of natural causes, a breakage experiment was carried out in an attempt to determine the kinds of breakage patterns that might result from hammerstone percussion. Photograph: Kate Johnson, San Diego Natural History MuseumCMS-Figure-2

The rocks show clear marks of having been used as hammers and an anvil and the scientists believe the stones are too heavy to have been carried there in the flow of a stream.

“in association with sharply broken bones of this mastodon and then we also found a large rock in association with these bones which poses a puzzle, because the remains of this mastodon were found in a silt layer and geological processes that deposit silt are not going to be carrying rocks of this size,”

– Study leader Tom Deméré, paleontologist at the San Diego Natural History Museum

‘Humans’ as in Homo Sapiens?

It is uncertain what kind of human species that did this, if these were, in fact, modern humans in the form of Homo sapiens or any other human species, possibly Denisovian, Homo erectus, or even Neanderthal.

“if it is modern people, we suddenly have additional signs that indicate that they traveled from Africa much earlier than we have thought so far.”

– Tom Deméré

The generally accepted theory for the early human migration and settlement of North America has modern humans, Homo sapiens, entering across a land bridge connecting Siberia and Alaska between about twenty-seven thousand and eleven thousand years ago.

There is a genetic technique that uses mutations in a population’s genome as a sort of a “clock”, it provides us with an estimation of the first common ancestor of Native Americans to have lived about 20,000 years ago. So if these are indeed early settlers of Homo Sapiens, they would have died out without leaving any genetic traces in later settlers.

More evidence is required and more data is needed that clearly points to the fact that the rocks were actually used by humans. For example, an age estimate of the sediment layer in which the mastodon was found, or even greater, of course, would be direct evidence such as human remains.

These findings present many interesting questions, however. The results are presented this week in the scientific journal Nature. Click here to view an interview with Tom Deméré.

When humans first migrated to the Americas has long been a controversial issue. The oldest clear evidence is about 15,000 years old. In addition, there are a few older sites with what appears to be man-made tools in Calico Hills in California and Pedra Furada in Brazil. These are between 80,000 and 20,000 years old, but it is highly uncertain if these remains are real tools. The new discovery in California will certainly also be questioned. But if the information turns out to be correct, if would force a full revise of what we know about the first Americans and early human migration.


Steven R. Holen et al. A 130,000-year-old archaeological site in southern California, USA. Nature April 26, 2017. DOI: 10.1038 / nature22065