Here's a subject for a monster movie—only there would be no victims, because it happened about 3 billion years ago. According to a new theory, the first life form on Earth was a mega-organism that once filled the world's oceans, then split up into parts that later spawned the ancestors of all living things. Dubbed LUCA, the massive organism was actually a network of cells. But they worked as one to survive on this turbulent planet, the New Scientist reports.
Unable to make the exact proteins they needed, these cells swapped them instead—effectively creating a massive gene pool that survived together. Around the time oxygen appeared in the atmosphere—2.9 billion years ago, if you're counting—they split into single-celled bacteria, archaea, and complex cells called eukaryotes that eventually led to plants and animals. Not all scientists are buying the notion, however: "It's a plausible idea," says an MIT scientist. But he "honestly can't tell" if it's true. (Read about ancient gas clouds that scientists say seeded the entire universe.)