We have several layers of crust but they separated because of the desity level differences. The lighter material cruet layers rose upwards and the heavier materials caused them to drop further down
Mid-ocean ridges extend to all of Earth's oceans. Mid-ocean ridges lie under thousands of meters of water. Mid-ocean ridges spread additional crust on the ocean floor. I'm not sure about the the remaining statement but I know for sure that these three statements are true.
In respect to the low pressure center, the frontal squall line is out in front of the low pressure system thus an extra tropical cyclone squall line would also be called a "cold front."
