Milky Way spirals boost Earth crust formation

Earth’s crust builds up faster when the Solar System surfs through one of four spiral arms of the Milky Way. Researchers measured the decay of uranium in the ancient continental crust in Greenland and Australia to study how it formed between 2.8 and 3.8 billion years ago. They found that, every 200 million years or so — in tune with Earth passing through the Milky Way — the rate of crustal production increased. One explanation could be that denser areas of the galaxy dislodge more comets from the Oort cloud, which rain down on Earth, melting the crust and causing more magma to bubble up and congeal.