THAT AS SOON AS LIFE EXISTED,
IT BEGAN EVOLVING

Life, which arose about 4.7 billions years ago, could have remained limited to the first living kind of thing, accomplishing no more than eternal cycles of feeding and reproducing. But evolution began immediately. Already by 3.8 billion years ago the first simple cellular life forms had arisen. By about 3.0 billion years ago, already some were photosynthesizing.

MORE INFO:

• One time-line for evolving life is provided on the Wikepedia page Timeline of Evolution.
• Scientific American magazine provides an online essay by Stephen Jay Gould called The Evolution of Life on Earth.
• Berkeley University produces a page entitled Mechanisms: The Processes of Evolution.
• About.com explains how rocks, even very old ones, can be dated, on a page called About Isotopic Dating: Yardsticks for Geologic Time