New dating technique shows multiple meteors struck the Earth 790,000 years ago

A new analysis of tektites, gravel-sized objects made of natural glass and formed from terrestrial debris ejected when meteorites collide with the Earth’s surface, has revealed that multiple cosmic impacts took place in various parts of the world approximately 790,000 years ago.

Dr. Mario Trieloff, a geoscientist at Heidelberg University in Germany, and his colleagues used a new, more accurate dating technique based on naturally-occurring isotopes to investigate rock glasses retrieved from various locations in Asia, Australia, Canada, and Central America.

As they report in a paper to be appear in the April 2016 edition of Geochimica et Cosmochimica Acta, the samples are all virtually identical in age, despite the fact that, in some cases, they have significantly different chemistry. This indicates that a series of separate impact events must have occurred at roughly the same time, the study authors explained in a statement.

picture of tektites used in the study

Some of the tektites used in the study. Credit: Heidelberg University

Tektites are formed when terrestrial material melts following a meteorite impact, is launched into the air and then hardens into glass, and Dr. Trieloff’s team said that they can determine when and where projectiles struck the planet’s surface, how often, and how large those objects were.

Natural disasters, lower surface temperatures would have followed

The researchers explained that scientists had long known about the existence of tektites in the Australasian region, from Indochina to southern Australia. Smaller rock glass samples called microtektites were also collected in deep-sea drill cores off the coast of Madagascar and in the Antarctic, and samples from Central America and Canada were analyzed as well.

Dr. Trieloff, lead author Dr. Winfried Schwarz and their fellow geoscientists used the 40Ar-39Ar dating method to analyze the decay of naturally occurring 40K isotope, and found that there must have been a cosmic impact approximately 793,000 years ago, plus or minus 8,000 years.

Tektites from Canada were similar in terms of chemical composition to those from Australia or the Antarctic, the authors said, suggesting that they may have traveled the same “flight routes,” provided the recovery sites were actually where the rock glass samples landed. The composition of the tektites recovered from Central America differed from the others, however.

“These tektites are clearly different in their chemical composition, and their geographical distribution also shows that they come from separate impacts,” said Dr. Schwarz. “Surprisingly our age estimates prove that they originated 777,000 years ago with a deviation of 16,000 years. Within the error margin, this matches the age of the Australasian tektites.”

“The distribution of the tektites and the size of the strewn field indicate that Earth-striking body was at least a kilometer in size and released an impressive one million megatons of TNT energy within seconds of impact,” the doctor added. Such an impact would have had dire consequences, as it would have caused widespread fires, earthquakes and/or tsunamis, and the amount of dust ejected into the atmosphere would have blocked sunlight and lowered surface temperatures.


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