Question

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:

Step1: Recall biological timeline

Fossil - evidence shows first single - celled life forms appeared around 2.5 billion years ago. 130 million years ago is too recent for first single - celled life. 1.5 billion years ago is after some more complex life developments started to occur in the timeline. 4.1 billion years ago is close to Earth's formation and before conditions were likely suitable for life. 2.5 billion years ago is consistent with scientific understanding of the appearance of first single - celled organisms.

Answer:

2.5 billion years ago