The heart begins to beat during the period of prenatal development.

Atree root breaking a rock into smaller fragments is an example of both and mechanical weathering. when rocks are exposed to heat, they which can contribute to thermal stress. when harmful gases, such as sulfur dioxide and nitrogen oxide, react with water in the atmosphere, they can produce the agent of erosion involved in stream erosion is when the ground is so saturated that it can't absorb rainfall or when rain falls so quickly that the ground can't absorb the water, forms. a/an is a huge, heavy, moving body of ice that picks up rocks and sand and erodes the ground beneath it as these materials scrape across it. hot arid climates are prone to erosion by rows of trees and shrubs planted to protect fields from wind erosion are known as