A team of geoscientists from Heidelberg University discovered multiple cosmic impacts affected our planet with global consequences approximately 790 000 years ago. Researchers have dated the so-called tektites rock glassed from different parts of the world, which originated from impacts of asteroids or comets, to reach this conclusion. The age of tektites from around the globe was shown to be identical, which indicates separate impacts must have happened around the same time.
The signs pointing at a major event of such impact have long been present, according to Prof. Mario Trieloff, leader of the research. The tektites, a type of rock glasses which arise from the impact as terrestrial material melts, provided evidence to support the claim.
"We have known about such tektites for some time from the Australasian region," said Winfried Schwarz, the first author of the study. These rock glasses form a strewn field that stretches from Indochina to the southernmost tip of Australia. Smaller tektites, known as microtektites, were also discovered in deep-sea drill cores off the coast of Madagascar and in the Antarctic. The rock glasses had been strewn over 10 000 km (6 213.7 miles), with some of them even leaving the earth's atmosphere.
The Heidelberg scientists used a dating method based on naturally occurring isotopes that allowed them to date the tektites more accurately than ever. Their studies show that the samples collected from Asia, Australia, Canada and Central America are virtually identical in age, although, in some cases, their chemistry differs markedly.
Tektites from Australia. The force of the impact hurled the glass bodies thousands of kilometers. Some left the Earth's atmosphere and acquired their flanged edge on re-entry into the atmosphere (bottom left). Image credit: Institute of Earth Sciences, Heidelberg University
The research group at the Institute of Earth Sciences and the Klaus Tschira Laboratory for Cosmochemistry uses isotope measurements to determine the age of craters caused by the impact of extraterrestrial rocks. "That's how we know when, where and how often projectiles struck the earth, and how big they were," explained Prof. Trieloff.
"Our data analysis indicates that there must have been a cosmic impact about 793 000 years ago, give or take 8 000 years," said Dr. Schwarz.
The Heidelberg scientists also studied samples from Canada and Central America. The Canadian rock glasses had the same chemical composition and age as the Australasian tektites and could have covered similar "flight routes" as objects found in southern Australia or the Antarctic. Other finds must first confirm whether the recovery sites are really where the tektites initially landed or whether they were carried there by people.
The rock glasses from Central America are also tektites – the first specimens were found at the sites of Mayan worship while hundreds of other findings have been made in Central America. "These tektites are clearly different in their chemical composition, and their geographical distribution also shows that they come from separate impacts. 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."
These findings suggest there were multiple cosmic impacts approximately 790 000 years ago. In addition to the events in the Australasian and Central American regions, a smaller collision at around the same time created the Darwin crater in Tasmania. "The distribution of the tektites and the size of the strewn field indicate that the earth striking body was, at least, a kilometer in size and released an impressive one million megatons of TNT energy within seconds of impact."
According to the scientists, the consequences of the impacts were dire. Fire and earthquakes spread for hundreds of kilometers around the site of impact while ocean impact would have triggered hundreds of meters high tsunamis. At the global level, dust and gases were ejected into the upper levels of the atmosphere, blocking sunlight and lowering surface temperatures. Biomass production was also affected, although, at the time, it did not result in global mass extinction as in the case of the dinosaurs approximately 65 million years ago.
Featured image: Tektites of different shapes from Australia. The force of the impact hurled the glass bodies thousands of kilometers. Some left the Earth's atmosphere and acquired their flanged edge on re-entry into the atmosphere. Credit: Institute of Earth Sciences, Heidelberg University