The impact of a meteorite ranges from an Alabama woman’s giant bruise to the end of the dinosaurs. But one meteorite's crater has eluded scientists for almost a century, despite the fact that it scattered glass confetti across one-tenth of the Earth’s surface. Now, experts at the Earth Observatory of Singapore have released a study, published in the Proceedings of the National Academy of Sciences, providing new evidence for the crater’s location.
The first clue to the meteorite’s impact site came from the bits of glassy debris, called tektites, that it launched into the air about 800,000 years ago. The tektites landed across Antarctica, Australia and Asia, so geologist Kerry Sieh searched for signs of the crater in satellite imagery. Sieh’s search has taken years and led him down many dead-ends, Katherine Kornei reports for the New York Times, but ultimately a lava field in southern Laos turned up promising results. There, volcanic eruptions long ago covered the land in molten rock, building a layer of igneous rock up to 1,000 feet deep, which could have easily obscured the impact crater.
The research team began by analyzing previously published chemical characteristics of tektites found in Australia and Asia, and found evidence linking them to the Laotian lava field. They then estimated the age of the tektites and lava flows—the lava at the suspect site was younger than the lava around it—and measured the local gravitational field of the lava bed. Craters are often filled with less dense material that was broken apart on impact, and Sieh’s findings of a weaker gravitational pull provide more evidence of the impact crater's existence.
"There have been many, many attempts to find the impact site,” Sieh tells CNN’s Michelle Lim. “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."
By the new study’s calculations, the meteorite was about 1.2 miles wide and created a crater 8 miles wide and 11 miles long. It would have struck our planet at a speed fast enough to melt the Earth beneath it, material that was thrown into the air to create tektites. The impact also would have sent boulders flying at 1,500 feet per second, Leslie Nemo writes for Discover, some of which Sieh spotted in a hill that was cut through by a road a few miles away from the suspected impact site.
Although the evidence they present is thorough, it’s not quite rock-solid. In a commentary that accompanied the study, impact crater expert Henry Melosh writes that Sieh and his team “present the best candidate yet for the long-sought source crater,” but adds, “one of my impact-savvy colleagues read the paper and was unconvinced. As with all possible impact craters, proof will rest on finding shock-metamorphosed rocks, minerals, and melt.”
Melosh points out that the crater is smaller than previously expected for this meteorite, and that it would have had to land at an unusually shallow angle to create the oval shape that Sieh’s team proposes. To provide the strongest evidence that this is the crater they’ve been looking for, scientists would have to drill through the lava flows, which are in a tropical jungle, and recover rock samples from below.
Sieh tells Nemo that he would be supportive of anyone who wants to complete that work.