In 1992, a group of archaeologists found something extraordinary buried below a sound berm next to the San Diego freeway in Southern California.
They had been called in during a freeway renovation to do some excavation because the fossil-laced earth of the California coast often yields scientific treasures.
After digging about three meters below the construction area, Center for American Paleolithic Research archaeologist Steve Holen was deep into a pristine layer of soil that hadn’t been disturbed for millennia.
There, he found what appeared to be an abandoned campsite, where humans had left stone tools and hammered mastodon bones behind.
This wasn’t too unusual; it’s fairly well-established that humans were hunting mastodons in the Americas as early as 15,000 years ago.
But when Holen’s colleagues used several techniques to discover the age of the bones, the numbers sounded crazy.
Test after test showed that the bones had been buried more than 100,000 years ago.
The result flew in the face of everything we think we know about the spread of humanity across the globe.
It took 24 years before Holen and his fellow researchers were certain enough to publish their findings in Nature. Now, based on a reliable dating method using Uranium decay rates and years of repeated tests, the researchers say that an unknown type of early human lived in California roughly 130,000 years ago.
If true, it completely changes the story of how humans reached the Americas.
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