World’s Oldest Space Pebbles Found in Australia
The tiny meteorites slammed into Earth about 2.7 billion years ago and captured clues to the planet’s early atmosphere.
About 2.7 billion years ago, tiny meteorites the size of sand grains rained down on a primeval landscape, sampling our planet’s ancient atmosphere in the process.
The not-so-great balls of fire—now the oldest micrometeorites ever found—started out as hunks of mostly iron and nickel. But as they careened through Earth’s upper atmosphere, roughly 47 miles (75 kilometers) above the planet’s surface, they felt the burn and crystallized, forming droplets mostly made of iron oxides.
These oxides suggest that the upper atmosphere of the time was about 20 percent oxygen, in line with modern levels. That’s a surprise for the Archean eon, a time when Earth’s atmosphere closer to the surface seems to have been almost oxygen free.
The finding, described on May