Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

[EX Q]: Question: Groundwater does what to the rock beneath the ground surface? Answer: erodes it
[EX A]: Groundwater erodes rock beneath the ground surface. Limestone is a carbonate and is most easily eroded.

[EX Q]: Question: What is the invisible force that pulls things to earth? Answer: gravity
[EX A]: Gravity cannot be seen. It does not require things to touch. Gravity is an invisible force. Many things are pulled to the Earth by gravity. Can you think of some things that fall toward the Earth?.

[EX Q]: Question: What is the main function of the cardiovascular system? Answer: to transport
[EX A]:
Many ecosystems have changed because of human actions. The human species is responsible for a range of environmental problems.