how life began
WE KNOW LIFE GOT ITS START around 4 billion years ago, when a drop in the Earth's temperature produced conditions that allowed the first organ-isms to thrive. Beyond that, the details of our origin story are still fuzzy. Most researchers agree that the key to the emergence of living things lies in DNA's single-stranded cousin, RNA. At some point this molecule, along with a handful of proteins, found itself sur-rounded by a membrane of fatty acids.
This was the first protocell, which over time would develop the ability to gener-ate its own energy, allowing it to grow and reproduce. Every single plant, an-imal, and itty-bitty bacterium on the planet is descended from that incredibly simple original organism. The exact trajectory very early life took isn't entirely clear. This flowchart shows what we know about how all living things came to be—and the spots along the way where we still have questions.