Rocks were eroded to form soil. Molten rock warmed Earth's interior. Earth's gravity accumulated to modern levels. Volcanoes exploded to form mountaintop lakes.
I gave my students this multiple choice question: Before large trees could grow on Earth, what had to happen first?

Only one answer is correct among these 4 choices:
- Rocks were eroded to form soil.
- Molten rock warmed Earth's interior.
- Earth's gravity accumulated to modern levels.
- Volcanoes exploded to form mountaintop lakes.

Could you tell me which one is correct?

Rocks were eroded to form soil.