New species evolved within a few thousand years of the Chicxulub Impact
TL;DR
Imagine the worst day in Earth's history: 66 million years ago, a giant asteroid slammed into what is now Mexico's Yucatan Peninsula, wiping out the dinosaurs and about 75% of all species on Earth. The oceans were especially hard hit. Tiny shelled creatures called foraminifera — think microscopic snails that float in the ocean — were nearly completely wiped out. Scientists used to think it took around 30,000 years before new species of these creatures started showing up. But this new study used a clever trick: measuring a rare type of helium (helium-3) that rains down from space at a steady rate, like a cosmic clock, to figure out exactly how fast sediment was piling up on the ocean floor. By doing that, they could measure time far more precisely. What they found was shocking — brand new species were appearing in the fossil record less than 2,000 years after the asteroid hit. That's incredibly fast for evolution. In fact, up to 10 brand new species appeared within a window of just 3,500 to 11,000 years across six different ocean locations around the world.
Abstract The immediate aftermath of the Cretaceous/Paleogene (K/Pg) mass extinction (ca. 66 Ma) in the marine realm was characterized by the initial recovery of productivity and the originations of new species. These major events are recorded in sediments a few centimeters above the K/Pg boundary and are typically dated via planktic foraminiferal biostratigraphy. The first Paleocene planktic foraminifer biozone is Zone P0, defined as the interval between the extinction of Cretaceous species and the first appearance of the new Paleocene taxon Parvularugoglobigerina eugubina. Constraining the age of the top of the global Biochron P0 is crucial for understanding how quickly this initial diversification occurred. However, the long-accepted value, ~30 k.y. after the boundary, is based on the assumption of constant sedimentation rates across the K/Pg boundary. We provide a new calibration for this important biostratigraphic marker using published records of 3He, a proxy for instantaneous sedimentation rates, from six K/Pg boundary sites. We find Biochron P0 durations between 3.5 k.y. and 11.1 k.y., with an average of 6.4 k.y. Taxonomic concepts vary among researchers, but as many as 10 new species of planktic foraminifera have been observed within Zone P0, with many more reported at or just above its top. Based on our new calibration, the first of these new species appeared <2 k.y. after the Chicxulub impact. The ages and order of these first appearances vary slightly from site to site, suggesting biogeographic differences between sites as novel taxa evolved and dispersed.
- 1Biochron P0 durations at six K/Pg boundary sites range from 3.5 k.y. to 11.1 k.y., with an average of 6.4 k.y., far shorter than the previously accepted ~30 k.y. estimate.
- 2The first new species of planktic foraminifera appeared less than 2,000 years after the Chicxulub impact, demonstrating extraordinarily rapid post-extinction speciation.
- 3Up to 10 new species of planktic foraminifera evolved within Zone P0, with many more appearing at or just above its top.
- 4New calibration of Biochron P0 used helium-3 (3He) as a proxy for instantaneous sedimentation rates across six K/Pg boundary sites, replacing the assumption of constant sedimentation rates.
- 5Slight variation in the ages and order of first appearances among sites suggests biogeographic differences in the evolution and dispersal of novel taxa after the mass extinction.
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