Carl Sagan detected life on Earth 30 years ago—here's how his experiment is helping us search for alien species today

It's been 30 years since a group of scientists led by Carl Sagan found evidence for life on Earth using data from instruments on board the Nasa Galileo robotic spacecraft. Yes, you read that correctly. Among his many pearls of wisdom, Sagan was famous for saying that science is more than a body of knowledge—it is a way of thinking.