The Earth's rocky outer crust solidified billions of
years ago, soon after the Earth formed. This crust is not a solid
shell; it is broken up into huge, thick plates that drift atop the soft,
underlying mantle.
The plates are made of rock and drift all over the globe; they move both
horizontally (sideways) and vertically (up and down). Over long
periods of time, the plates also change in size as their margins are
added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles (80 to 400 km) thick.
<span>The best answer is (d) water from snowmelts. The American Southwest has many mountains that catch moist air moving westward (from the Pacific) that falls as snow during the winter. The snow melts gradually during the spring and summer when there is little precipitation. The melted snow runs off the mountains into rivers and streams that can be tapped by irrigation pumps. The snowmelt also sinks into the ground, replenishing underground aquifers that can be tapped by wells in the valleys where farming takes place.</span>
Was it the size? I thought I heard it once but I'm not really sure.
