planetary scientists increasingly suspect that comets (frozen balls of dust and ice) and ice-laden meteorites crashing into the primordial Earth probably provided most of the planet’s water—and perhaps much of the organic material—necessary for life.

Organic molecules have been detected in comets such as the Hale-Bopp, and, in a recent study, researchers simulated those cosmic crash landings by using a gas gun to fire metal projectiles at 16,000 miles per hour into blocks of ice containing some of the same chemicals that make up comets. The shock wave and heat generated by the impact created molecules that formed amino acids, the building blocks of proteins.

Yet the very same objects that gave this planet life could also spell its demise. Astronomers predict that a comet or asteroid large enough to cause global devastation will smash into the Earth about every 100 million years or so.

Fortunately, if such a comet or asteroid were to arrive sooner than expected, we are constructing observational systems to discover and track near-Earth objects, conceivably providing us with sufficient time to pre-empt catastrophe.