Factor in Extinction of the Dinosaurs – Potentially a Comet Impact

A team of scientists based in the eastern part of the United States have published details of a paper that suggests that the extraterrestrial object that struck the Earth and marked the end of the dinosaurs may have been a comet.  The New Hampshire based research team outlined their theory at the forty-fourth Lunar and Planetary Science Conference which was being held in Texas.

Chicxulub Impact

It was father and son team Luis and Walter Alvarez and their study of the iridium-rich clay layer that marked the Cretaceous/Tertiary geological boundary across so many parts of the world, that first led to the theory that there had been a meteorite or asteroid object collision that had led to the deposition of iridium – a rare Earth element.

It was the discovery of the almost 190 kilometre wide Chicxulub crater in the Yucatan peninsula of Mexico that provided the “smoking gun” evidence that there had been an extraterrestrial impact some 65 million years ago that led to the demise of the Dinosauria and around seventy percent of all terrestrial life.  The theory that such a catastrophic event might have been a causal factor in the mass extinction that followed has now been largely accepted by the majority of the scientific community.

The actual date of the impact has even been calculated to around 66 million years ago, plus or minus either way a few thousands of years for margin of error.

To read more about the dating evidence: Dating the Cretaceous Mass Extinction.

Cretaceous Comet

However, this new paper proposes that a smaller, faster travelling comet collided with our planet and the culprit was not a larger, slower moving asteroid or meteorite.  The New Hampshire team (from Dartmouth College), studied the sediments and rock strata at the Yucatan site and concluded that the crater might have been caused by the impact of a much smaller object, but one that was travelling at immense speed.

The smaller mass of the colliding object would have reduced the kinetic energy released but the devastation caused could have been amplified by the much greater speed that a body like a comet would be travelling compared to a rocky meteorite or asteroid.

In an analysis of a second rare Earth element deposited  – osmium the team were able to hypothesise that the impact object deposited much less debris than previously thought.

Higher Levels of Iridium

The research team also concluded that the widely reported higher levels of iridium had been previously overstated.  This data was then examined in conjunction with the known geo-physical nature of the Chicxulub impact crater and the team deduced that to deposit on Earth that much iridium and osmium a meteor or asteroid of over five kilometres wide would be needed, but if a rocky object of that size smacked into the geology of the Gulf of Mexico a much larger crater would have resulted.

To read more about scientific studies of the Chicxulub crater: Getting to the Bottom of the Chicxulub crater.

The End of the Dinosauria

For a smaller object to have created the Chicxulub crater on impact it would have had to have had a greater terminal velocity and the research team point to a long-period comet as being  a more likely candidate for the harbinger of dinosaur doom.  Long period comets are believed to be remnants left over from the formation of our solar system.  They consist of rocks, dust and ice and they orbit the sun, often in very eccentric trajectories, with some comets taking millions of years to complete one circuit.  Other comets such as the famous Halley’s comet are known as a short-period comets – having an orbit of less than 200 years.

Other scientists challenge the Cretaceous comet impact idea, suggesting that a lot of debris may have been ejected up into and beyond our atmosphere.  If a lot of the impact object material was ejected into space and left our atmosphere then the evidence tips in favour of a larger rocky object such as an asteroid.

Whatever it was, the devastation caused was certainly terrific with earthquakes, fire storms, enormous tidal waves and acid rain.  It is likely that much of the light and heat from the sun was obscured by dust in the atmosphere, shrouding the Earth in what has been termed a “nuclear winter”.

Dinosaurs, marine reptiles, the last of the pterosaurs along with many types of invertebrate, plants and marine plankton became extinct.  Flowering plants including the hardwood trees, along with mammals also suffered but it was from the end of the Age of Reptiles that flowering plants and mammals rapidly diversified becoming the dominant and most prominent floras and faunas in most ecosystems today.

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