The asteroid impact at the end of the Cretaceous period, about 65 million years ago, was an extinction event that wiped out 75 percent of all species on our planet—including the non-birdlike dinosaurs. It was caused by the collision of an asteroid 10 to 15 kilometers wide. Especially devastating was the global winter that followed, which is thought to have halted photosynthesis on a massive scale. As a result, all large-bodied animals (vertebrates) became extinct.
Yet life bounced back, leading eventually to our current biosphere. Just how astoundingly fast it bounced back is the topic of a new research paper published by Tyler Lyson from the Denver Museum of Nature & Science and colleagues.
The asteroid that killed off the dinosaurs also had devastating effects on the mammals that were around at the time. But a fossil record newly discovered by the authors in Colorado shows that just 100,000 years later, mammals had recovered enough to be about the same size they were just before the asteroid strike, with a maximum body weight of about 8 kilograms. Within 200,000 years, their maximum body mass had climbed to more than 20 kilograms, and 700,000 years after the impact some mammals weighed nearly 50 kilograms. Along with the rise in body mass came an increase in biodiversity, not only for animals but also for large plants. Protein-rich bean plants appeared 700,000 years after the impact, and are likely one of the reasons mammals reached a size close to what we see today within a million years of the asteroid impact. From a geological viewpoint, that’s just a blink of an eye.
The study by Lyson and colleagues provides important insights into how fast mammals took over after the demise of the dinosaurs. From a broader viewpoint, it shows the robustness of a biosphere once it’s established on a planet. When Earth warmed up again after the impact, photosynthesis powered on again—in the oceans via plankton and on land via plants—and the race was under way to repopulate our planet and fill in the free ecological niches.
Asteroid impacts are quite common in our Solar System, as they almost certainly are in other planetary systems. So any habitable world with a biosphere will be exposed to occasional mayhem coming from the sky. While some impacts are large enough to eradicate a whole biosphere, they also can have positive outcomes for life. For example, they may be able to distribute microbial life from one planet to another. Or they can spur evolution. Based on Lyson’s study, we now know how fast this can happen. Once again, we see evidence that life is much hardier than most of us thought.