The first cells on earth were approximately how old?

• A. 5 billion years ago
• B. 3.5 billion years ago
• C. 1 billion years ago
• D. 4 billion years ago

Answer: (B)

The timing question is about when life first appeared on Earth. The best-supported date for the appearance of the first cells—simple, single-celled organisms—is about 3.5 billion years ago. This is based on fossil and geochemical evidence, including microfossils and stromatolites in ancient rocks and carbon isotope patterns that point to biological activity at that time. Earth itself is about 4.5 billion years old, so 3.5 billion years is after Earth formed and long before complex life, making it the most reasonable estimate for the origin of the first cells.

The other options don’t fit as well. 5 billion years ago would be before Earth existed, and 1 billion years ago is far too late for the origin of life. 4 billion years ago is closer in time but less supported by the strongest fossil evidence, which centers around around 3.5 billion years.