Photosynthesis all but stopped, killing most of the plant life, extinguishing the phytoplankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. But the over-all view is consistently grim. Scientists still debate many of the details, which are derived from the computer models, and from field studies of the debris layer, knowledge of extinction rates, fossils and microfossils, and many other clues. Meanwhile, giant tsunamis resulting from the impact churned across the Gulf of Mexico, tearing up coastlines, sometimes peeling up hundreds of feet of rock, pushing debris inland and then sucking it back out into deep water, leaving jumbled deposits that oilmen sometimes encounter in the course of deep-sea drilling. Measurements of the layer of ash and soot that eventually coated the Earth indicate that fires consumed about seventy per cent of the world’s forests. As the Earth rotated, the airborne material converged at the opposite side of the planet, where it fell and set fire to the entire Indian subcontinent. Computer models suggest that the atmosphere within fifteen hundred miles of ground zero became red hot from the debris storm, triggering gigantic forest fires. Its substance, mingling with vaporized Earth rock, formed a fiery plume, which reached halfway to the moon before collapsing in a pillar of incandescent dust. The asteroid may have sown life throughout the solar system, even as it ravaged life on Earth. Mathematical models indicate that at least some of this vagabond debris still harbored living microbes. A 2013 study in the journal Astrobiology estimated that tens of thousands of pounds of impact rubble may have landed on Titan, a moon of Saturn, and on Europa and Callisto, which orbit Jupiter-three satellites that scientists believe may have promising habitats for life. Mars was eventually strewn with the debris-just as pieces of Mars, knocked aloft by ancient asteroid impacts, have been found on Earth. Over millions of years, bits of it found their way to other planets and moons in the solar system. Some of the ejecta escaped Earth’s gravitational pull and went into irregular orbits around the sun. In addition, an inverted cone of liquefied, superheated rock rose, spread outward as countless red-hot blobs of glass, called tektites, and blanketed the Western Hemisphere.
Much of the material was several times hotter than the surface of the sun, and it set fire to everything within a thousand miles. Instead, the initial blowout formed a “rooster tail,” a gigantic jet of molten material, which exited the atmosphere, some of it fanning out over North America. The energy released was more than that of a billion Hiroshima bombs, but the blast looked nothing like a nuclear explosion, with its signature mushroom cloud. When Earth’s crust rebounded, a peak higher than Mt. Picture the splash of a pebble falling into pond water, but on a planetary scale. Within two minutes of slamming into Earth, the asteroid, which was at least six miles wide, had gouged a crater about eighteen miles deep and lofted twenty-five trillion metric tons of debris into the atmosphere.
The result was a slow-motion, second-by-second false-color video of the event. In that moment, the Cretaceous period ended and the Paleogene period began.Ī few years ago, scientists at Los Alamos National Laboratory used what was then one of the world’s most powerful computers, the so-called Q Machine, to model the effects of the impact. The asteroid struck a shallow sea where the Yucatán peninsula is today. The air in front was compressed and violently heated, and it blasted a hole through the atmosphere, generating a supersonic shock wave. That’s because it was not a star but an asteroid, and it was headed directly for Earth at about forty-five thousand miles an hour. If you watched for an hour or two, the star would have seemed to grow in brightness, although it barely moved. If, on a certain evening about sixty-six million years ago, you had stood somewhere in North America and looked up at the sky, you would have soon made out what appeared to be a star.
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