Researchers find proof of global cooling after Chicxulub asteroid impact

May 13, 2014 by Marcia Malory report
Yucatan chix crater. Credit: NASA

(Phys.org) —Scientists have long believed an asteroid that collided with the Earth around 66 million years ago, leaving an enormous crater near Chicxulub Mexico, caused the demise of the dinosaurs and many other living things. Ash and dust thrown into the air during the impact would have caused darkness and a drop in global temperature, leading to a mass extinction. Johan Vellekoop of Utrecht University in the Netherlands and his colleagues have found evidence of this global cooling by studying lipids in sediment formed at the same time as the collision. The research appears in the Proceedings of the National Academy of Sciences.

The Cretaceous-Paleogene (K-Pg) extinction event was one of the largest mass extinctions on Earth. A 180-kilometer-wide impact crater near the town of Chicxulub, in Mexico's Yucatan peninsula, is evidence of the asteroid impact believed to have caused it. While proof of the collision exists, until now, scientists have found no evidence of an impact winter occurring afterward. This could be because the period of global cooling was very brief, lasting from months to decades. In addition, many of the algae that produce the chalky fossils used to study ocean surface temperatures became extinct themselves.

Vellekoop and his team looked for signs of global cooling in sediment at the Brazos River in Texas. There, layers of sediment formed at the K-Pg boundary contain high levels of iridium, which would have come from the asteroid. These layers contain many broken shells, which could have been remnants of a tsunami caused by the impact.

The researchers studied lipids produced by the microbe Thaumarchaeota. The composition of these lipids changes as ocean temperatures change. An examination of lipids preserved in sediment at the K-Pg boundary revealed that after the impact, ocean temperatures fell an average of two degrees Celsius, with drops of up to seven degrees Celsius in some places. This decrease in temperature lasted up to several decades, a timescale supported by models and by evidence of species migration.

The sudden cooling would have caused a great amount of stress on living things and therefore been a key contributor to the mass extinction. When dust injected into the atmosphere rained out, the ocean surfaces would have become acidic, resulting in yet more stress for surface-dwelling organisms.

Vellekoop's team found that a stable warm period followed this short period of global cooling. Large-scale mortality, forest fires and the vaporization of rock would have released greenhouse gases into the atmosphere, causing this global warming. The team thinks the research should help increase understanding of the effects of rapid climate change.

Explore further: Study suggests dinosaurs killed off by more than one asteroid

More information: Johan Vellekoop, Appy Sluijs, Jan Smit, Stefan Schouten, Johan W. H. Weijers, Jaap S. Sinninghe Damsté, and Henk Brinkhuis. "Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary." PNAS 2014 ; published ahead of print May 12, 2014, doi:10.1073/pnas.1319253111

Abstract
The mass extinction at the Cretaceous–Paleogene boundary, ∼66 Ma, is thought to be caused by the impact of an asteroid at Chicxulub, present-day Mexico. Although the precise mechanisms that led to this mass extinction remain enigmatic, most postulated scenarios involve a short-lived global cooling, a so-called "impact winter" phase. Here we document a major decline in sea surface temperature during the first months to decades following the impact event, using TEX86 paleothermometry of sediments from the Brazos River section, Texas. We interpret this cold spell to reflect, to our knowledge, the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere, blocking incoming solar radiation. This impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis.

Press release

Related Stories

Researchers say a comet killed the dinosaurs

April 4, 2013

In a geological moment about 66 million years ago, something killed off almost all the dinosaurs and some 70 percent of all other species living on Earth. Only those dinosaurs related to birds appear to have survived. Most ...

Recommended for you

New study sheds light on end of Snowball Earth period

August 24, 2015

The second ice age during the Cryogenian period was not followed by the sudden and chaotic melting-back of the ice as previously thought, but ended with regular advances and retreats of the ice, according to research published ...

Earth's mineralogy unique in the cosmos

August 26, 2015

New research from a team led by Carnegie's Robert Hazen predicts that Earth has more than 1,500 undiscovered minerals and that the exact mineral diversity of our planet is unique and could not be duplicated anywhere in the ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Maggnus
5 / 5 (4) May 13, 2014
For those keeping score, this statement:
Large-scale mortality, forest fires and the vaporization of rock would have released greenhouse gases into the atmosphere, causing this global warming.
gives an example of warming having been driven by CO2 and other GHGs injected into the atmosphere.

Shootist
1 / 5 (2) May 13, 2014
For those keeping score, this statement:
Large-scale mortality, forest fires and the vaporization of rock would have released greenhouse gases into the atmosphere, causing this global warming.
gives an example of warming having been driven by CO2 and other GHGs injected into the atmosphere.



The Chicxulub impact did hit a carbonate shelf, and in an instant injected more co2 into the atmosphere that all of man's activities since the invention of fire. Approx 27000 km^3 of limestone (CaCO3) *poof*.

As Doctor Seitz says, all the carbon in the earth, be it coal, petroleum, natural gas, limestone or (some) diamonds, was once in the atmosphere as CO2.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.