Nav: Home

Extraterrestrial impact preceded ancient global warming event

October 13, 2016

Troy, N.Y. -- A comet strike may have triggered the Paleocene-Eocene Thermal Maximum (PETM), a rapid warming of the Earth caused by an accumulation of atmospheric carbon dioxide 56 million years ago, which offers analogs to global warming today. Sorting through samples of sediment from the time period, researchers at Rensselaer Polytechnic Institute discovered evidence of the strike in the form of microtektites - tiny dark glassy spheres typically formed by extraterrestrial impacts. The research will be published tomorrow in the journal Science.

"This tells us that there was an extraterrestrial impact at the time this sediment was deposited - a space rock hit the planet," said Morgan Schaller, an assistant professor of earth and environmental sciences at Rensselaer, and corresponding author of the paper. "The coincidence of an impact with a major climate change is nothing short of remarkable." Schaller is joined in the research by Rensselaer professor Miriam Katz and graduate student Megan Fung, James Wright of Rutgers University, and Dennis Kent of Columbia University.

Schaller was searching for fossilized remains of Foraminifera, a tiny organism that produces a shell, when he first noticed a microtektite in the sediment he was examining. Although it is common for researchers to search for fossilized remains in PETM sediments, microtektites have not been previously detected. Schaller and his team theorize this is because microtektites are typically dark in color, and do not stand out on the black sorting tray researchers use to search for light-colored fossilized remains. Once Schaller noticed the first microtektite, the researchers switched to a white sorting tray, and began to find more.

At peak abundance, the research team found as many as three microtektites per gram of sediment examined. Microtektites are typically spherical, or tear-drop shaped, and are formed by an impact powerful enough to melt and vaporize the target area, casting molten ejecta into the atmosphere. Some microtektites from the samples contained "shocked quartz," definitive evidence of their impact origin, and exhibited microcraters or were sintered together, evidence of the speed at which they were traveling as they solidified and hit the ground.

Atmospheric carbon dioxide increased rapidly during the PETM, and an accompanying spike in global temperatures of about 5 to 8 degrees Celsius lasted for about 150,000 years. Although this much is known, the source of the carbon dioxide had not been determined, and little is known about the exact sequence of events - such as how rapidly carbon dioxide entered the atmosphere, how quickly and at what rate temperatures began to rise, and how long it took to reach a global high temperature.

One clue can be found in a sudden shift in the ratio of carbon isotopes (atoms containing a number of neutrons unequal to the protons in their nucleus) in certain fossils from the time period. In particular, Foraminifera, or "forams," produce a shell whose chemistry is representative of atmospheric and ocean carbon isotopes. The research team initially set out to examine the ratio of carbon isotopes in Foraminifera fossils over time, to more closely pinpoint events during the PETM.

"In sediment records, when you look at the ratio of carbon-12 to carbon-13 in a particular species, you see that it's stable and then it abruptly shifts, wiggles back and forth and slowly returns to pre-event values over hundreds of thousands of years," Schaller said. "This evidence defines the event, and tells us that the atmosphere changed, in particular adding carbon from a source depleted in carbon-13. A comet impact on its own may have contributed carbon to the atmosphere, but is too small to explain the whole event and more likely acts as a trigger for additional carbon releases from other sources."

As a source of fossils, the team used sediment cores - cylinders of sediment extracted vertically from sediment deposits with a hollow bit - known to correspond to the time period of the PETM. Sediments near the top are more recent, those further down are older, and signature layers indicating known events are used to calibrate the timescale represented in the sample. The team chose cores from three sites - Wilson Lake and Millville in New Jersey, and Blake Nose, an underwater site east of Florida - known for a rich sedimentary record of the time period.

As Schaller tells it, the discovery of microtektites was "completely by accident." Ordinarily, the team passes samples through sieves of various sizes, to isolate samples most likely to contain forams. The tektites, which are smaller than most forams, would have been largely removed in this process.

"We were having lousy luck looking for forams, and I was frustrated. I went to the lab and dumped a sample on the sorting tray without sieving it, and there it was," Schaller said. "It was a stunning moment. I knew what I was looking at was not normal."

Once the team made the discovery, they obtained a sample from a fourth site - Medford - where the unit is naturally exposed at the surface, to rule out the possibility that the samples had been contaminated by the drilling process. The Medford samples also contained microtektites.
-end-
About Rensselaer Polytechnic Institute

Research at Rensselaer fulfills the vision of The New Polytechnic, an emerging paradigm for higher education which recognizes that global challenges and opportunities are so complex, they cannot be addressed by even the most talented person working alone. Rensselaer serves as a crossroads for collaboration -- working with partners across disciplines, sectors, and geographic regions, to address global challenges -- and addresses some of the world's most pressing technological challenges, from energy security and sustainable development to biotechnology and human health. The New Polytechnic is transformative in the global impact of research, in its innovative pedagogy, and in the lives of students at Rensselaer.

Rensselaer Polytechnic Institute, founded in 1824, is America's first technological research university. The university offers bachelor's, master's, and doctoral degrees in engineering; the sciences; information technology and web sciences; architecture; management; and the arts, humanities, and social sciences. Rensselaer faculty advance research in a wide range of fields, with an emphasis on biotechnology, nanotechnology, computational science and engineering, data science, and the media arts and technology. The Institute has an established record of success in the transfer of technology from the laboratory to the marketplace, fulfilling its founding mission of applying science "to the common purposes of life." For more information, please visit http://www.rpi.edu.

Rensselaer Polytechnic Institute

Related Atmosphere Articles:

Primitive atmosphere discovered around 'Warm Neptune'
A pioneering new study uncovering the 'primitive atmosphere' surrounding a distant world could provide a pivotal breakthrough in the search to how planets form and develop in far-flung galaxies.
NASA's MAVEN reveals Mars has metal in its atmosphere
Mars has electrically charged metal atoms (ions) high in its atmosphere, according to new results from NASA's MAVEN spacecraft.
Northern oceans pumped CO2 into the atmosphere
The Norwegian Sea acted as CO2 source in the past.
Study opens new questions on how the atmosphere and oceans formed
A new study led by The Australian National University has found seawater cycles throughout the Earth's interior down to 2,900km, much deeper than previously thought, reopening questions about how the atmosphere and oceans formed.
How a moon slows the decay of Pluto's atmosphere
A new study from the Georgia Institute of Technology provides additional insight into relationship between Pluto and its moon, Charon, and how it affects the continuous stripping of Pluto's atmosphere by solar wind.
Fossil fuel formation: Key to atmosphere's oxygen?
For the development of animals, nothing -- with the exception of DNA -- may be more important than oxygen in the atmosphere.
Researchers dial in to 'thermostat' in Earth's upper atmosphere
A team led by the University of Colorado Boulder has found the mechanism behind the sudden onset of a 'natural thermostat' in Earth's upper atmosphere that dramatically cools the air after it has been heated by violent solar activity.
New biochar model scrubs CO2 from the atmosphere
New Cornell University research suggests an economically viable model to scrub carbon dioxide from the atmosphere to thwart global warming.
Venus-like exoplanet might have oxygen atmosphere, but not life
The distant planet GJ 1132b intrigued astronomers when it was discovered last year.
Middle atmosphere in sync with the ocean
In the late 20th century scientists observed a cooling at the transition between the troposphere and stratosphere at an altitude of about 15 kilometers.

Related Atmosphere Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.