Describe what Earth's magnetic field looks like and how it has changed through time.

In which state was more than 100 billion tons of coal mined in 2005?

Scientists discover two populations of mice on either side of a major river. the two populations have almost identical genes but the mice from one side cannot breed with mice from the other. this is most likely because

Asquirrel population lives in an area. over many years, a river in that area grows wider and stronger, eventually forming a canyon. the squirrel populations on the two sides of the canyon can no longer mate with each other and ultimately form distinct species. this is an example of