Origins of Civilisation · San Diego County, California, USA

Cerutti Mastodon Site, California

The most radical dating claim ever published in a major journal: that someone was smashing mastodon bones in California 130,000 years ago — ten times earlier than the accepted arrival of humans.

Mainstream: Bones deposited c. 130,000 years ago; human involvement rejected by most researchersAlternative: Claimed human activity c. 130,000 years ago (2017 Nature paper)32.67°, -117.05°

Origins

At a glance

Cerutti Mastodon Site, California — Photo: Owen Allen · CC BY 2.0

In 1992, road crews expanding a freeway in San Diego County exposed the bones of a single mastodon in fine-grained sediments. Field paleontologist Richard Cerutti recognised something odd: heavy limb bones broken in a fresh, spiral pattern, fragments arranged in clusters, and large cobbles among the otherwise fine sands that appeared to bear impact and wear marks. A quarter-century later, in 2017, a team dated the deposit to around 130,000 years ago and argued in the journal Nature that the breakage was the work of unknown humans. If true, it would rewrite the peopling of the Americas by more than 100,000 years.

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The mainstream view

What archaeology says

The mainstream reaction to the 2017 Nature paper was, and remains, deep scepticism — not of the date of the bones, but of the claim that people made the breakage. The deposit itself was dated by Thomas Deméré, Steven Holen, James Paces and colleagues using uranium-thorium methods to roughly 130,700 years ago, and that geological age is not seriously disputed. What is disputed is everything built on top of it.

Critics led by the veteran geoarchaeologist C Vance Haynes and others argued that the fractures and the marks on the cobbles are far more plausibly explained by ordinary, non-human forces: the heavy earth-moving equipment that exposed the site, natural sediment loading, or transport in high-energy flows. Gary Haynes and colleagues later showed that bone assemblages closely resembling Cerutti occur at sites where no human involvement is suspected, produced by trampling, carnivores and geological processes alone. The absence of the usual corroborating evidence weighs heavily: no stone tools of recognisable type, no cut marks, no hearths, no other artefacts, and no human remains — only broken bones and rocks whose interpretation is ambiguous. Given that the next-oldest widely accepted American sites are barely a fifth as old, most archaeologists apply the maxim that extraordinary claims require extraordinary evidence, and find the case unproven.

The consensus verdict is that Cerutti most likely records natural bone breakage in a 130,000-year-old deposit — remarkable geology, but not an archaeological site.

Key evidence cited

No recognisable stone tools, cut marks, hearths, other artefacts or human remains at the site
Fractures and stone marks plausibly caused by heavy freeway-construction equipment or natural forces
Assemblages resembling Cerutti documented at sites with no suspected human involvement
The next-oldest accepted American sites are roughly five times younger, isolating the claim
Extraordinary-claim standard unmet: broken bones and rocks alone are interpretively ambiguous

The alternative view

What the skeptics propose

The site's defenders — principally Steven Holen, Thomas Deméré, Kathleen Holen, Richard Fullagar and their co-authors — mount a detailed, physically grounded case that this was deliberate hominin activity. They point to the spiral, green-bone fracture pattern characteristic of bones broken while fresh, to the selective breakage of the thickest limb bones (consistent with marrow extraction), and to the spatial arrangement of fragments around large cobbles they interpret as hammerstones and anvils bearing matching impact damage and use-wear. Crucially, they argue that much of the breakage and many of the diagnostic surfaces are coated in thick crusts of pedogenic carbonate, showing the damage occurred long ago in the ground, not during the 1992 excavation.

To test the mechanism, the team conducted experimental archaeology, breaking elephant limb bones with large stones and reproducing the same fracture types, cone flakes and impact notches seen at Cerutti — arguing that heavy machinery, trampling or water transport do not replicate this signature. In their replies to Haynes and to Ferraro and colleagues, the Holen group maintain that the stratigraphy was intact before excavation, that the geological age is sound, and that the pattern of broken bones and modified stones is best explained by percussion by a tool-using hominin, whether an early Homo sapiens or an archaic human such as a Denisovan, Neanderthal or Homo erectus that had somehow reached the Americas.

Their case does not claim to identify who the toolmakers were, only that the physical evidence of deliberate bone-breaking is real. Steelmanned, it is a serious argument from taphonomy and experiment; its central weakness is that it asks the world to accept a lone, artefact-poor site against an overwhelming absence of any other trace of humans in the Americas for the next hundred thousand years.

Key evidence cited

Uranium-thorium dating placing the bone deposit at about 130,700 years ago
Spiral green-bone fractures and selective breakage of the thickest limb bones (marrow extraction)
Large cobbles interpreted as hammerstones and anvils with matching impact damage and use-wear
Pedogenic carbonate crusts on broken surfaces indicating ancient, not modern, breakage
Experimental replication of the fracture signature by percussion, not by machinery or trampling

Genuinely open questions

Did the spiral fractures and stone marks form 130,000 years ago, or during the 1992 excavation?
If humans were present, which hominin were they, and why is there no other trace of them for 100,000 years?
Can natural processes alone produce the full Cerutti signature — the fractures, cone flakes and stone wear together?

Worth knowing

The Cerutti claim would push human presence in the Americas back so far that it predates the earliest confirmed Homo sapiens fossils outside Africa — meaning the alleged toolmakers, if real, may not have been our species at all, but some archaic human who reached California before we had even left our home continent.