What happened when Earth's first atmosphere collapsed? Will mark you as brainliest! - it created oxygen

-it formed the oceans

-it triggered an ice age

-it fell as rain, watering the earliest plants

Explanation:

solar radiation would break atmospheric water into oxygen, which would react with carbon on the Earth to form carbon dioxide. The air would still be too thin to breathe. The lack of atmosphere would chill the Earth's surface.Plants and land animals would die

the answer to your question is:

c. complementary base-pairing