Maybe the first life on Earth was part of an 'RNA world.' Artur Plawgo/Science Photo Library via Getty Images How life on Earth started has puzzled scientists for a long time. And it still does.

How did life begin on Earth? While scientists have theories, they don't yet fully understand the precise chemical steps that led to biology, or when the first primitive life forms appeared.

The history of life on Earth began long after the planet's formation 4.6 billion years ago. During the earliest stage of ...

It isn’t easy to figure out how the Earth was built, because it happened 4½ billion years ago, and no one was there to watch. So scientists have had to look at what the Earth looks like now and at all ...