Mars wasn’t always so dry and dusty. The Red Planet’s ancient ocean was sprayed right off the planet in violent bursts of solar wind, billions of years ago. The rest of its atmosphere was blasted away, too. Martian waterfalls, rivers, lakes, and the piles of clouds reflected in them—all gone, forever.
When scientists announced earlier this month they’d figured out the mechanisms behind Mars’s atmospheric loss, several people had the same question: Will Earth end up like Mars someday?
It makes sense to ask. After all, when a huge ocean covered about half of Mars’s Northern Hemisphere, the planet may have looked a lot like Earth does now.
Today, Earth’s atmosphere is fairly well protected by a global magnetic shield. But it won’t be that way forever. Earth will someday lose its oceans, too. What will the planet be like when that happens? And which ocean will be the last to go?
Planetary scientists have several theories about how Earth might dry up, but little else to go on. “To my knowledge there’s no evidence that it’s ever happened in the last 500 million years, for which we have good records,” said Paul Renne, the director of the Berkeley Geochronology Center. “If it did happen, it’s hard to imagine that water would survive anywhere on Earth—no lakes, rivers, glaciers. This would presumably mean 100 percent extinction of biota.”