geology

Multiple Comet and Asteroid Impacts 790,000-Years-Ago, Study Finds

About 790,000 years ago, scientists suggest that multiple cosmic impacts on Earth had catastrophic consequences, such as earthquakes and fires for hundreds of kilometers around the impact zone, and ocean impacts that would have caused tsunamis hundreds of meters high.

The evidence comes from analyzing rocks known as tektites. Tektites are glass rocks that are formed when an asteroid or comet impact sends melted rock hundreds of kilometers in the air, sometimes leaving the atmosphere – upon re-entry the rock cools into glass, usually forming spherical shapes.

asteroid-multiple-impacts-2

An artists impression of multiple asteroid and comet impacts. Image credit: K. Sturry

Dr. Winfried Schwarz and his team of geoscientists at Heidelberg University measured the decay of naturally occurring isotopes in tektites from Asia, Australia, Canada and Central America, with a precision never achieved before.

Results showed that there was an impact in the Australasia region about 793,000 years ago.

“We have known about such tektites for some time from the Australasian region,” said Schwarz. “Our data analysis indicates that there must have been a cosmic impact about 793,000 years ago, give or take 8,000 years.”

Surprisingly, tektites from Canada had the same chemical composition and age as the Australasia samples, suggesting they came from the same “flight routes.”

tektites

Tektites of different shapes from Australia. Image credit: Heidelberg University

The Central American tektites “are clearly different in their chemical composition, and their geographical distribution also shows that they come from separate impacts,” said Dr. Schwarz.

But here’s where it gets really interesting: “Surprisingly our age estimates prove that they (the Central American tektites) originated 777,000 years ago with a deviation of 16,000 years. Within the error margin, this matches the age of the Australasian tektites,” explained Dr. Schwarz.

The findings led the team to conclude that Earth was struck by multiple cosmic impacts approximately 790,000 years ago. Additionally, scientists know of a small impact that happened around the same time in Tasmania that appears to support the results.

According to scientists, land impacts would have caused fires and earthquakes for hundreds of kilometers around the impact site, while massive tsunamis would have been created by ocean impacts. Dust and gases ejected into the atmosphere from the collisions would have blocked out sunlight, cooling surface temperatures globally. Although the effects were pronounced, scientists say it did not result in a global mass extinction.

The findings were published in the journal Geochimica et Cosmochimica Acta.

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