Earth’s geological history could have a lot to say about our future in space. Every time we investigate a huge crater like Chicxulub, the Yucatan impact site that may have played a role in the demise of the dinosaurs, we’re reminded that the Solar System is an active and dangerous place. And the evidence multiplies. The Wilkes Land crater in east Antarctica may bear witness to the Permian-Triassic extinction that destroyed almost all life on Earth some 250 million years ago.
A defensive system in space with the capability of deflecting dangerous Earth-crossing objects is vital for species survival, whether the next strike occurs in ten or a hundred thousand years. But it’s a hard concept to sell because Earth’s major strikes, unlike those on the Moon, for example, tend to be obscured over time. Absent a visible historical context, a relatively minor strike like the 1908 Tunguska event can come to be seen as a quirky accident rather than evidence of a larger threat.
Now comes word of an explosion over or into the Laurentide ice sheet north of the Great Lakes some 13,000 years ago, causing the extinctions of big mammals like the mammoth and the mastodon by triggering a round of climatic cooling. Here again we have no obvious crater to look at, but rather layers of sediment drawn from numerous sites around the North American continent. In the sediments, a team led by James Kennett (UC Santa Barbara) found amounts of iridium and specks of nano-diamond, along with small spheres of glass and carbon. All that adds up, says the research team, to an explosion 12,900 years ago.
The BBC does a good job covering this story, with this quote from Kennett on the extinctions:
“All the elephants, including the mastodon and the mammoth, all the ground sloths, including the giant ground sloth – which, when standing on its hind legs, would have been as big as a mammoth …All the horses went out, all the North American camels went out. There were large carnivores like the sabre-toothed cat and an enormous bear called the short-faced bear.”
As to human populations, they would have lived through a 1,000 year period of cooling, an era known as the Younger Dryas whose effects were global and may have influenced the beginning of farming in the Middle East. In North America, the impact on the Clovis people, who hunted mammoths, may have been catastrophic. Such speculations enlivened the American Geophysical Union meeting in Acapulco when presented there last week. Let’s hope they also energize a new round of thinking about what a human presence in space can do to head off future catastrophes.