Riley Black writes:

Of all the species that have ever lived on our planet, more than 99 per cent are extinct. Most of these organisms disappeared through the constant shuffle of ecological and evolutionary change. But not all. Many species have vanished in a geological snap during mass extinctions – truly catastrophic events where the rate of extinction vastly outpaces the origin of new species. For a time, these ecological disasters were thought to drive a great flourish of new lifeforms in the aftermath. It turns out that supposition is wrong.

Consider the cataclysm that ended the Cretaceous Period around 66 million years ago. A chunk of space rock more than 7 miles wide smacked into what’s now the Yucatán Peninsula. The debris and ejecta thrown into the atmosphere heated up on the way back down, causing oven-like temperatures all over the planet before a chilly post-impact winter settled in, almost halting photosynthesis for three years. Before the impact, the likes of Tyrannosaurus and Triceratops were thriving. After, only birds were left to carry on the legacy of the ‘terrible lizards’ in what would eventually be called the Age of Mammals. The impact, palaeontologists used to argue, toppled dinosaurs from dominance and allowed our mammalian relatives and ancestors to thrive. A mass extinction, in other words, was the prerequisite for a new evolutionary burst that featured mammals.

But the classic tale of extinction and recovery doesn’t hold up anymore. What the fossil record tells us about the nature of life on Earth does not line up with the traditional view in which mass extinctions refresh life’s diversity as if they were blazes required to reinvigorate fire-adapted forests. Life’s greatest radiations, palaeontologists are learning, were decoupled from mass extinctions. Instead, those radiations seem to have come when organisms transcended anatomical and environmental barriers to inhabit a new niche. The origin of complex eyes, the interplay of species as some organisms became adapted to land, and similar events were far more important than mass extinction to evolution’s most vigorous moments in time – a testament to the complexity of our planet’s biodiversity and a warning for life’s future on this planet. [Continue reading…]