Asteroids are dangerous, but they might also be the key to life on Earth

Trying to piece together the appearance of life on Earth is a little like looking through a kaleidoscope. There are competing theories for where Earth’s water came from, and there’s incomplete evidence for how the moon formed and what role it played in life’s emergence. There are a thousand other questions, each with competing answers. Sometimes, contradictory research is published within days of each other.