The initial idea of panspermia began in ancient Greece but wasn't fully accepted until the early 1900s, when German physicist Svante Arrhenius outlined just how this could happen. In the vastness of space, dormant seeds and spores resistant to the harsh conditions hitch a ride onto particles and travel the universe. Some eventually are drawn in by the gravity of a planet and end up on the surface. If the conditions are right, they can rise from their slumber and start growing, thriving, and evolving. The idea is hard to believe and for over a century, there was little evidence to prove the postulate. Yet by the turn of the 21st century, some of the clues began to fall into place.