19 octobre 2016

Une comète a frappé la Terre il y a 55,6 millions d'années

Extrait de la nouvelle:

In recent years, the warm period — known as the Paleocene-Eocene Thermal Maximum (PETM) — has become a major point of interest for researchers as it’s perhaps the best past analog to today’s human-induced climate change.

Atmospheric carbon dioxide increased rapidly during this warming event, and an accompanying spike in global temperatures of about 5 to 8 degrees Celsius lasted for approximately 150,000 years.

Among the suggested drivers are the intrusion of flood basalts into carbon-rich marine sediments, carbon degassing from volcanoes, and an extraterrestrial impact on Earth.

Sorting through samples of sediment from the time period, Rensselaer Polytechnic Institute geochemist Dr. Morgan Schaller and co-authors discovered evidence of a comet strike in the form of tiny spherical droplets of glass called microtektites.

These glassy spherules are thought to form when an extraterrestrial object hits the planet and sprays out vaporized material that solidifies while flying through the air.

“This tells us that there was an extraterrestrial impact at the time this sediment was deposited,” Dr. Schaller said.

“The coincidence of an impact with a major climate change is nothing short of remarkable.”

The researchers spotted the spherules at the base of a layer of fine clay believed to mark the start of the PETM.

The samples came from drill cores taken in suburban Millville and Wilson Lake, NJ, and from a streambank in nearby Medford, NJ.

The 30-foot-thick section of fine material, known as the Marlboro clay, is found in several areas along the U.S. East Coast, and appears to have been laid down rapidly.

All the microtektites came from a 7- or 8-inch layer at its base.

A fourth sample, correlated to the same time, came from a deep-seabed core taken off Bermuda.

“It’s got to be more than coincidental that there’s an impact right at the same time,” Dr. Schaller said.

“If the impact was related, it suggests the carbon release was fast.”



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