Fair-ish and Balanced-ish
Wednesday, June 02, 2004
Death of the Dinosaurs - A New Theory
What killed the dinosaurs is a question which interests many. It now seems that a asteroid strike played a contributing role, however, how exactly it did this is a matter for debate. Firestorms, global warming and global cooling have all been suggested. Now a new theory has been proposed.
This theory is primarily based on two different observations; the pattern of extinction among vertebrates, and the discovery of tiny particles known as spherules at the K-T boundary (this is a geological layer which was caused by the asteroid impact).
It appears that the event which killed the dinosaurs didn't kill at random. While the dinosaurs died, many other groups survived. The survivors include fish, amphibians, lizards, snakes, turtles, crocodiles, birds and mammals (placental, monotreme, multituberculate, Gondwanatherian, dryolestoid and marsupials).
Spherules, on the other hand, are "formed from ejecta particles as they melt and incandesce on reentry". They have been found all over the world (well, techically, there are many unsampled areas of the global, but they have been found in places like New Zealand which are pretty far from the impact) at the K-T boundary.
So how do these two obervations link together? The authors suggest that the asteroid through massive quantities of material into the upper atmosphere. They then heated up emitting large amounts of infra-red radiation. The authors write:
The intense IR radiation would have originated from the entire sky. Darkness would have been eliminated worldwide for several hours and shadows curtailed. Shadowing effects would have been restricted to a direct proportion of the fraction of the sky blocked by a massive object. An organism at the foot of a lengthy vertical cliff, for example, would have been spared radiation from just under half the sky. It would not have been sufficient to shelter in a gully, under an isolated tree, or even uder a sparsely forested canopy. Life confined to Earth's surface would have perished well before incineration. After ignition temperature was reached, fires would not have spread from one area to another in the usual way. Rather fires would have ignited nearly simultaneously at places having available fuel... The fires (on land with sufficient fuel) would have been especially intense because IR radiation coming from the entire sky continued to add heat even as the fires burned.
Sounds pretty bad. Fortunally, it is possible to live through a intense IR blast lasting a couple of hours + associated firestorm. The key is to get something between you and radiation. Soil and water are both quite good at this. So animals which burrow, or swim can survive. Meanwhile, animals which can't die. This was pretty bad news for the dinosaurs. Mammals, lizards, birds and so on, survived the initial firestorm. This in itself doesn't mean an escape from extinction, but rather, it does give the species a fighting change.
Source: Douglas Robertson, Malcolm McKenna, Owen Toon, Sylvia Hope and Jason Lillegraven Survival in the first hours of the Cenozoic GSA Bulletin May/June 2004. Pages 760 - 768).