It may come as something of a surprise, but various volcanic eruptions and meteor impacts are, at present, missing their volcanoes and impact scars. We’ve found clues to their geological mischief, but so far the suspects elude identification. One such 800,000-year-old impact is proving particularly mysterious: All that can be found at present is a gigantic breadcrumb trail of debris, found predominantly over Australasia.
Now, reporting in the journal Geochimica et Cosmochimica Acta, an international team of meteorite mavericks have revealed that they’ve found some more of these vitreous breadcrumbs at the ends of the Earth, in the Transantarctic Mountains. The crater still eludes them, but the team from Imperial College London, Vrije University, and the Case Western Reserve University are narrowing it down with each latest treasure haul, including this one.
Once upon a time, a sizeable meteor penetrated our planet’s atmosphere and slammed into the crust. The sheer momentum of the object guaranteed that it generated not just a fairly voluminous crater, but a molten spray of debris, which eventually solidified into glassy beads known as tektites.
Currently, these have been found over an area of more than 150 million square kilometers (57 million square miles), from South-East Asia to Australia – more than 15 times the area of the US.
The distribution of these roughly pea-sized spherules, along with the age of the sediments they’re buried in, indicate that the perhaps 1 to 2.5-kilometer (0.6 to 1.6-mile) impactor’s crater was about 20 kilometers (12 miles) across, and formed 0.8 million years ago – relatively recent in geological terms. Although not exactly small, human land-use changes and sedimentological processes mean that craters, even young ones, can quickly disappear from view.
As the study notes, this field of debris – also including even smaller microtektites – is known as the “Australasian strewn field,” one of four terrestrial examples known to science. This one happens to be by far the largest, though, and it appears, with this latest study, it just got a little bigger.
Digging through an accumulation of unconsolidated debris dumped by an ancient glacier on Antarctica, the team managed to find some new types of incredibly fine microtektites. Although they could have turned up here through various means, their sheer concentration (200 particles per kilo) suggests they were directly deposited there post-destruction.
Geochemical analyses of these miniature marvels revealed that they were once incredibly hot: volatiles vulnerable to high temperatures were boiled away and depleted relative to more resilient refractory elements.
In fact, their geochemical makeup matches that found in the Australasian strewn field members, but in this case, they represent the highly vaporized remains of the impact event. All in all, this suggests they were throw the furthest from the crater, which extends the strewn field by a further 800 kilometers (about 500 miles) or so.
Far from just extending the size of the strewn field, it also fills in more of the geographical jigsaw puzzle as to where the crater actually is. The size of the tektites increase dramatically the closer you get to Vietnam, whereupon they become fist-sized. Along with higher concentrations of volatile elements, these facts imply that it’s likely to be somewhere there.
Dr Matthew Genge, a master of meteorites at Imperial, suggests the crater has been buried somewhere where sediment accumulates rapidly, like a river delta, but there's a chance it's offshore instead. Either way, these geological detectives are closing in on where X marks the spot.