New research led by the U. Exeter wildFIRE Lab in collaboration with BRE Centre for Fire Safety Engineering and Imperial College London proves the theory that Global Firestorms didn’t kill the dinosaurs.
The research featured on BBC Spotlight, BBC Radio and the media continues the hot debate as to what killed 80% off all life on Earth at the End of the Cretaceous?
Until the 1980s this catastrophic loss of life was a mystery, but then scientists found a clue – trace abundances of the element iridium in rocks of this age. Iridium falls to Earth with extraterrestrial objects. This key finding suggested that there was a major extraterrestrial collision with the planet and that this could be responsible for the mass kill of species.
Ten years later scientists found the 65 million year old, 180km wide, Chicxulub crater on the Yucatan Peninsula in Mexico finally providing the smoking gun that could explain the apparent chaos that ensued at the end of the Cretaceous. A 180km wide crater suggests that an approximately 10km wide asteroid or comet hit the Earth. The impact of such a large object would have released a huge amount of energy. The asteroid itself was vaporised as it smashed into the Earth and in doing so vaporised and blasted out particles of the rock that it hit. A huge glowing ball of hot rock and vapour rushed up from the impact site at huge speeds ejecting it way above the atmosphere up into space. As it hit the cold of space it decelerated, cooled and rained back through the atmosphere re-solidifying forming rock spherules. As these fell through the atmosphere they were subject to frictional-drag which caused them to become super heated. As these particles rain down through the atmosphere they delivered a thermal pulse to the ground.
This heat pulse has widely been suggested to have ignited global wildfires and has been cited as a possible cause of extinction on land. But how do you go about estimating the amount of heat generated from an impact? And how do you go about testing whether the heat pulse could start a wildfire?
New computer modeling techniques have enabled scientists to generate better estimates of the heat pulse resulting from this impact. What they found was that the heat flux wasn’t evenly distributed across the surface of the Earth. Models have shown that a very short lived but high heat pulse was generated near to the impact site but far away (such as all the way in New Zealand), the peak heating was lower but would be delivered for a much longer period.
Humanity has not been unlucky enough to observe first hand the effects of a large impact so we have to turn to the laboratory in order to study the effect that it might have. In order to do this Earth Scientists have teamed up with Fire Safety Engineers to use state-of-the-art apparatus usually used to test the flammability of furnishings and materials, to recreate the heat pulse from the asteroid impact. This provided, for the first time, the ability to test whether the heat pulse from the impact could start fires in plant material.
So how likely is the global firestorm hypothesis? The research reveals that the short sharp blast of heat felt closer to the impact could not have ignited live plants but the longer drawn out pulse a long way from the impact may have started fires in some locations, implying that localized fires may have occurred but critically global firestorms were unlikely. More importantly these findings turn our understanding of the effects of the heat pulse on its head as the effects of the heat would have been greater further away from the impact. This means that Earth scientists will have to reassess their understanding of the fossil record of life. Until now they have read the fossil record of this event by assuming that the heat pulse generated was worse close to the crater but now patterns of extinction and survival must be reinterpreted by considering a more severe heat pulse further away.
Blogged by Claire Belcher