In geology, a graded<span> bed is one </span>characterized by<span> a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones.</span>
The evidence of the theory of continental drift can be found on the edges of the tectonic plates. For example, the boundary of the African Plate and the Eurasian plate is in the Mediterranean Sea, just south of the island of Crete. At this boundary, scientists have observed that the Eurasian Plate is sliding under the African Plate at a rate of three to four centimeters per year as the African Plate drifts north
The Earth's atmosphere is mostly Nitrogen ~ 78% and Oxygen ~21% gas.
