These deep-ocean<span> currents are driven by differences in the </span>water's<span> density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline </span>circulation<span>. In the Earth's polar regions </span>ocean water<span> gets very cold, forming </span>sea<span> ice.</span>
Contour lines determine the steepness of the land by how close they are together. Generally, contour lines rise to a particular scale (e.g. a line for every ten metres), therefore, if the contour lines are closer together then the height of that particular area has risen more steeply than if the contour lines are further apart where the steepness has increased more gradually.
Fossils are the remains of plants and animals that have been preserved for millennia in stones under the Earth's surface. They contain the long chapters of the history of our Earth. Fossils tell us what the earth looked like many millions of years ago, what kind of animals and plants lived on its surface and how it was changing. Fossils show us a history of over a billion years old.
From the fossil from a dry, mountainous area we can conclude that the area was once underwater and over time the soil has risen as result of continental drift and uplift. So, a mountain was once the bottom of a prehistoric ocean or sea.
<span>Factors contributing to the west ward expansion of the United States include the discovery of gold, the Homestead Act, and the desire for adventure, land and riches. The answers are the third, fourth and fifth statements among the choices that you have included or posted.</span>
...asteroids and comets. Planets formed much later.
