What are the two main things that cause external changes on earth?
a. weathering and erosion
b. physical and chemical
c. sheet and continental glaciers
d. hot and cold temperatures

The two main things that cause external changes on Earth are A. hot and cold temperatures (D), as well as physical and chemical changes (B). Weathering and erosion (A) and sheet and continental glaciers (C) have an impact on the earth's external structure, but they are influenced by physical and chemical changes as well as hot and cold temperatures. Hot and cold temperatures are probably the biggest cause of external changes on the earth. Gravity causes sheet ice and continental glaciers to move. Heat causes the sheet ice to melt raising the sea levels and exposing more of the earth to the sun's hot rays. 

Afine-grained igneous rock forms as a result of slow cooling.