【古生物学】恐竜を絶滅させた小惑星の衝突現場における生物の急速な回復

Life recovered rapidly at the site of the asteroid impact that killed the dinosaurs, reports a paper published online this week in Nature.

Although most famous for finishing off the non-avian dinosaurs, the mass extinction at the end of the Cretaceous period, 66 million years ago, extinguished over 75% of all species. The extinction was triggered by an asteroid impacting the Earth in a shallow sea near Chicxulub, on Mexico’s Yucatan peninsula. The rate at which the global marine ecosystem recovered from the catastrophe varied, taking up to 300,000 years in the Gulf of Mexico and the North Atlantic, much slower than in other regions further from the impact crater. It had thus been suggested that an impact-related environmental effect, such as toxic metal poisoning, might have slowed recovery near the impact crater.

Christopher Lowery and colleagues analysed rock samples drilled up from beneath the crater, which preserve a record of the first 200,000 years after the impact. They examined the changes in various tiny fossils - the single-celled, shelled foraminifera and calcium-based nannoplankton - along with fossil traces of biological activity and the abundance of various elements (such as extra-terrestrially derived helium-3, the flux of which can be used to infer sedimentation rates).

The authors found that life recovered at the crater mere years after the catastrophe, with a diverse and highly productive ecosystem returning to Chicxulub within 30,000 years - far faster than at sites further away from the impact. The findings suggest that there was no impact-related control on recovery. Instead, the authors propose, ecological processes such as the interactions between organisms in the crater probably controlled recovery, highlighting the importance of such in understanding how ocean ecosystems respond to similar rapid extinction events.