Question

study the timeline. based on fossil evidence, about how long ago did the first single - celled life form appear on earth? 130 million years ago 1.5 billion years ago 2.5 billion years ago 4.1 billion years ago

Explanation:

The provided timeline explicitly marks "Single-celled life" at 4.1 BYA (billion years ago), which matches this option.

Answer:

4.1 billion years ago