Sunday SciKu | Overkill

For 20+ years, I’ve found the nonsense of the overkill hypothesis maddening. The idea is that humans are such efficient, warlike creatures that we arrive on new continents and murder everything we come across. The Neanderthals in Europe and the Diprotodons in Australia 42,000 years ago. The North American mammoths and mastodons 12,500 years ago. It’s the most obvious scientific farce I’ve ever heard, and yet for decades it’s remained the mainstream explanation for these recent extinction events. Really, this is nothing but the projection of our contemporary fears and guilts into the past, based on flimsy circumstantial evidence, turning science into a morality play for kindergarteners.

The obvious problem is this: Neanderthals and Diprotodons went extinct at the exact same time on opposite sides of the world. And during the Younger Dryas event 12,500 years ago, it wasn’t just mammoths that died out—it was 70% of North American megafauna, including sabretooth tigers, the American lion, 12-foot-tall short-faced bears, dire wolves, American camels, ground sloths the size of elephants, armadillos the size of Volkswagen Beetles—including even the Clovis people who were supposedly killing them. Stone age humans with spears didn’t hunt out all these massive species in a few hundred years and then kill themselves. How absurd is that? And yet most textbooks still say that’s what happened.

What actually did happen, though, is one of the deepest and most important mysteries in history. These weren’t just extinction events—big changes to the global environment were going on at the same time. There are really only two plausible explanations. There might have been a series of comet or asteroid impacts into the ice sheets and ocean, and we just haven’t found the craters. But more and more it’s looking like the real story is in the magnetic fields of the Earth and Sun, and researchers added more to the pile of evidence this week, looking at prehistoric kauri trees preserved in the bog swamps of New Zealand.

What they found was a huge increase in Carbon-14 right at the Laschamps Magnetic Excursion, 42,000 years ago. Just as the Neanderthals and Australian megafauna were going extinct, the Earth’s magnetic field was in the middle of a potential pole flip, and dropped as low as 6% of its normal strength. Carbon-14 is made in the atmosphere when cosmic rays (particles ejected from supernovae traveling near the speed of light) slam into nitrogen atoms, knocking off a proton and turning N-14 into radioactive C-14. With the Earth’s magnetic field so weak, there were way more cosmic rays reaching the atmosphere and way more C-14.

More and more we’re learning that cosmic ray penetration has a large influence on the climate. Increased cosmic rays cause a thinning of the ozone layer. They excite the silica-rich magma in volcanos, leading to increased stratospheric ash injections. They play a crucial role in cloud formation. All of these things result in rapid drops in the global temperature.

With the Earth’s magnetic field so weak, we had little shielding against solar storms and coronal mass ejections. Auroras during this time would have been global, sometimes coming close enough to the ground to create arc discharges—continent-wide lightning storms, lighting the forests on fire, creating black mat layers and nanodiamonds in the soil. They’d have seemed like fluorescent snakes spitting electricity and setting the entire world ablaze. With the ozone depleted, we had little protection from the sun’s UV light even in calm conditions. Cancer rates increased, pathogens mutated more rapidly.

This happened at the Laschamp Excursion 42,000 years ago, and it happened again during the Gothenburg Excursion 12,500 years ago. During the latter, a CME likely struck while North America was sun-facing in summer.

The picture is becoming clear: our ancestors weren’t butchers; they were survivors of a world we can’t even imagine, a Biblical apocalypse with fire in the sky, massive floods and continent-wide fires. They fled to caves to survive. They made red ochre—the pigment used in cave paintings—as primitive sunscreen, protecting them from the intense radiation. They found food and adapted as all these other animals were dying out. They lived through a catastrophe that the Neanderthals couldn’t. And that’s the only reason we’re here today, blaming them for it.

So when I see the handprints in the caves they sheltered in tens of thousands of years ago, they seem to me gestures of love and perseverance though an impossible barrier of time and trauma.


my brother’s palm
on the prison glass
red ochre


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