It came from outer space

Micrometeorites (space dust) that arrived on Earth 240 million years ago have been uncovered by Japanese researchers. The fossilised space dust, no larger than droplets of fog, is the oldest ever found by 50 million years.

Some 30,000 tons of space dust falls from space each year, but the almost all of it vaporises in the Earth’s atmosphere. Using the fragile micrometeorites that survive the fall, researchers can make guesses about cosmic conditions experienced by Earth.

Read more at Wired Science