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2019-01-17. Moon’s craters reveal recent spike in outer space impacts on Earth.

posted Jan 21, 2019, 5:44 PM by Alan Gould

By Paul Voosen, Science Magazine. [https://www.sciencemag.org/news/2019/01/moon-s-craters-reveal-recent-spike-outer-space-impacts-earth] For GSS A Changing Cosmos chapter 7 and Life and Climate chapter 9. Excerpt: It has long been thought that as the solar system grows older and stodgier, the number of asteroids and comets colliding with Earth and other planets has steadily gone down. But a new study reveals what appears to be a dramatic 2.5 times increase in the number of impacts striking Earth in the past 300 million years. ...Scientists used a thermal camera on NASA’s Lunar Reconnaissance Orbiter to examine the number of large, heat-retaining rocks in the moon’s craters; those rocks are eventually ground to dust by minute meteorite impacts. By looking at previously dated craters, these rocks have been established as a reliable dating technique—the more intact the rocks, the younger the crater. In the new study, the team found a surprising abundance of young craters, seemingly matching the number on Earth. That means, they write today in Science, that in its modern geological history, Earth is much better at retaining the features of impact craters than once thought, and that the recent proliferation coincides with an actual increase in the number of bombarding asteroids or comets. But scientists still don’t know what caused the uptick. Perhaps several large asteroids collided or otherwise broke up some 300 million years ago, their chunks slowly migrating out from the asteroid belt to bombard Earth, the researchers say. And that could have included the giant impact, 66 million years ago, that wiped out most of the dinosaurs....  See also New York Times article, What Happened to Earth’s Ancient Craters? Scientists Seek Clues on the Moon’s Pocked Surface. [https://www.nytimes.com/2019/01/17/science/craters-meteors-moon.html]