When did life (organisms) first appear on Earth?

• A. About 3.5 billion years ago
• B. About 65 million years ago
• C. About 540 million years ago
• D. About 4.6 billion years ago

Answer: (A)

Verified step by step guidance

1. Understand the timeline of Earth's history: Earth formed approximately 4.6 billion years ago, and life appeared much later. Familiarize yourself with key events in Earth's history to contextualize the options provided.
2. Recall that the earliest evidence of life on Earth comes from fossilized microorganisms found in ancient rocks. These fossils date back to approximately 3.5 billion years ago, which represents the first known appearance of life.
3. Eliminate incorrect options: About 4.6 billion years ago refers to Earth's formation, not the appearance of life. About 65 million years ago marks the extinction of the dinosaurs, and about 540 million years ago corresponds to the Cambrian Explosion, a period of rapid diversification of life forms.
4. Focus on the correct option: About 3.5 billion years ago aligns with the scientific evidence for the earliest life forms, such as stromatolites and microfossils.
5. Conclude that the correct answer is 'About 3.5 billion years ago,' as this is supported by geological and fossil evidence.