core mantle atmosphere hydrosphere
I gave my students this multiple choice question: The Late Heavy Bombardment was a period of extensive comet impact on Earth about 3.8 billion years ago. Scientists believe this period provided much of the matter now found in which part of the Earth system?

Only one answer is correct among these 4 choices:
- core
- mantle
- atmosphere
- hydrosphere

Could you tell me which one is correct?

hydrosphere