Wednesday, 12 October 2011

The First Animals To See The New World After The Cretaceous Extinction Event

CU-Boulder Professor Karen Chin studies the
ancient worm burrows under a stereomicroscope
When the world was struck by the Manhattan sized asteroid from the Baptistina Family, it was reduced to a hellhole in hours. It went from a place of deadly heat to cold in less than a day. A shock wave would have radiated out from the collision zone, carrying with its superheated rock and gas at many kilometers a second. This boiling hot surge would have killed most creatures within 100 kilometers of the site. Seconds later, powerful geological upheavals would have caused volcanic eruptions, earthquakes and tsunamis  around the world.

Huge clouds of dust would have filled the atmosphere, plunging the Earth into a 3 year long night. Plants and algae would have withered and died, while all other creatures dependent upon plants as a source of food would have suffered. The predators would have fared very poorly as well. Most life would have sheltered underground from the dust storms and freezing cold winds. This is how warm-blooded mammals survived these harsh conditions.

The nagging question is what returned to the surface of the Earth after the extinction event? Compelling new evidence suggests that it was the unassuming worms which gained a brief dominance over our planet. A team of scientists led by Professor Karen Chin from the geology department of the University of Colorado Boulder made a study of sediments dating to just after the KT boundary and found a series of mysterious trace fossils within the rocks which give clues as to the first creatures to see a new world without dinosaurs.

The Earth's history is often divided into zones governed by various animals. The Mesozoic is commonly referred to as the Age of Dinosaurs and the Cenozoic is the Age of Mammals. The period from 65 to 30 million years ago is less well known yet is referred to as the Age of Birds. In my opinion, the results of Professor Chin's research create a new biotic time period which existed just after to extinction of the dinosaurs; the Age of Worms.

By studying the sediments, the team found the presence of a series of fossilised worm burrows which existed just inches above the distinctive, iridium rich layer of rock that marks out the KT geological boundary.While the exact date of the asteroid impact and the formation of the burrows are unclear, Chin and her associates believe that the two events were just a few thousand years apart. The three dimensional burrows were found on the boundary between a siltstone and a coal-based outcrop in south west North Nevada.

They were made by a creature or creatures with similar dimensions to the common earthworm. With a horizontal position relative to the surface, it is likely that they are traces of feeding activities. The entire area was originally a large peat bog. It would have been very similar to the unappetising pools of grey sludge which often feature as a part of the topography as a fictional post-nuclear apocalypse. The world just after the asteroid would have been a wasteland, levelled by a blast of energy a billion times more powerful than the Hiroshima bomb.

Worms are a likely candidate for the first creatures to return to the surface of the Earth as they would have endured flooded habitats, low oxygen, no light and highly acidic conditions. Chin used work based upon plant fossils from before and after the KT extinction to characterise the environment. 'When we reconstruct past environments, soft-bodied animals like worms get short-shrift since they don't stand out in the fossil record like animals with mineralized skeletons,' states Chin. While this discovery does not give us much insight into how creatures returned to the Earth, it does offer a tantalising insight into the Earth's long, 4.5 billion year story.