Question

How many years ago did the oxygen-rich atmosphere form on Earth?

• A. 2000 Million year
• B. 2500 Million year
• C. 3000 Million year
• D. 3500 Million year

Answer 1

Answer:

A. 2000 Million year

• An oxygen-rich atmosphere was formed on Earth 2000 million years ago

• Photosynthesis began in the ocean about 2500-3000 million years ago

• Oceans formed on earth about 4000 million years ago

• Life in the oceans originated about 3800 million years ago