Scientists may have discovered the impact site of one of the largest meteorites to have ever hit Earth
A field of black glassy rock fragments, strewn across about 20% of Earth’s Eastern Hemisphere, resulted from the impact of a large meteorite about 790,000 years ago. Scientists believe they have now discovered the impact site, which they say lies buried beneath the Bolaven volcanic field in southern Laos.
The team says the large buried crater might be the long-sought source of the glassy blobs, or tektites, produced by the meteorite impact, which is the largest known young meteorite impact on Earth. “The Australasian strewn field, a horizon of glassy clasts (tektites) quenched from molten ejecta of a bolide impact, extends across about 1/10 of the Earth’s surface -- from Indochina to East Antarctica and from the Indian to western Pacific Oceans,” says the study published in the Proceedings of the National Academy of Sciences (PNAS).
It says, “The large crater from which these tektites originated has eluded discovery for over a century, although evidence has long pointed to a location somewhere within Indochina, near the northern limit of the strewn field. We present stratigraphic, geochemical, geophysical, and geochronological evidence that the ∼15-km diameter crater lies buried beneath a large, young volcanic field in Southern Laos.”
(Image courtesy of Kerry Sieh)
According to study author Jason Herrin from Nanyang Technical University, Singapore, there have been multiple attempts to find the impact site and suggestions range from northern Cambodia to central Laos, southern China, and from eastern Thailand to offshore Vietnam.
“But our study is the first to put together so many lines of evidence, ranging from the chemical nature of the tektites to their physical characteristics and from gravity measurements to measurements of the age of lavas that could bury the crater,” Herrin told MEA WorldWide (MEAWW).
He explains that the study of past impacts can give scientists an idea of what to expect if one should occur again.
“Knowing the ground zero location of the world’s youngest and most intact large impact deposit is critical for evaluation of the energy and after-effects of such a catastrophe. Astronomers have become increasingly good at spotting NEOs (Near-Earth objects) and predicting their paths. In order to make maximum use of this information, however, in the event that a major impact was unavoidable, we would need to know what to expect on the ground. This impact site, more than any other, offers an opportunity to study such an event,” Herrin told MEAWW.
The researchers presented four lines of evidence in the study, which include the chemical composition of the tektites that is consistent with the rocks at the Bolaven location. According to the team, geologic mapping and dating of rocks above the buried crater confirm that the crater could be buried by younger lavas.
“A low-density gravity anomaly at the proposed site could indicate the presence of a buried approximately 17 × 13-km crater. Further, a nearby outcrop (10-20 km southeast of the proposed impact site) of thick, crudely layered, bouldery sandstone and mudstone deposit containing fractured quartz grains within its boulder clasts is thought to be part of the proximal ejecta blanket,” says the study.
The team will now conduct further research. “We have only scratched the surface of the geology of the impact region. Continued stratigraphic characterization of the impact deposits, in more detail and with emphasis on high-energy processes, is one direction that our studies are going. Another direction will be working with our regional collaborators who are investigating the paleontology and even the anthropology of the impact to better understand its effects on the region and its inhabitants,” Herrin told MEAWW.