After the Asteroid Impact

Following the mass extinction 66 million years ago, life bounced back faster than expected.

Chicxulub, Mexico, as it looks today. Sixty-six million years ago, this was ground zero.

Last week at the Lunar and Planetary Science Meeting in Houston, a research team headed by Chris Lowery from the University of Texas Institute for Geophysics presented the first results of their work at the site of the asteroid impact that wiped out the dinosaurs at the end of the Cretaceous period 66 million years ago. The researchers have recovered nearly 1,000 meters of core material from Chicxulub Crater, located off the Yucatan Peninsula in the Gulf of Mexico. They’re looking to find out exactly what mechanism caused the mass extinction following the impact, and how life eventually came back in the crater.

According to their findings, life at ground zero bounced back astonishingly quickly. Not all kinds of organisms returned at the same time, however. Microorganisms that can reproduce rather quickly, and that float or drift in great numbers in the upper meters of the sea, came back sooner. Many of these were small photosynthetic organisms that harvest sunlight. The early returners included various types of single-celled microorganisms called foraminifera, including one species with the tongue-twisting name Parvularugoglobigerina eugubina. In fact, this particular organism is seen in the fossil record only after the impact, and may have been one of the first new species of plankton to evolve, just 30,000 years after the asteroid hit.

Organisms that live on or near the bottom of the sea had a much harder time recovering, and appear to have remained environmentally stressed for a long time. Foraminifera survived the impact in other parts of the world where conditions were less disastrous than at ground zero. Then they diversified and underwent evolutionary change rapidly. Eventually they re-settled the water column above Chicxulub Crater, and when that happened, it happened very quickly.

This provides us with a general lesson for life on Earth. No matter how grave the conditions, or how severe the blow to life in one particular location, that place will be resettled as soon as environmental conditions become bearable again—if there are other places where life was able to hunker down and stay protected. Challenge life, and its evolutionary toolset kicks in to deal with the new environmental conditions. Microorganisms generally deal much better with dramatically changing conditions than larger animals, so it was “game over” for the dinosaurs. But there are exceptions based on lifestyle. Our mammal ancestors—small burrowing animals—were better protected from the cataclysmic fallout of the asteroid impact than the dinosaurs were, and so eventually carried the day.

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