A basic law of geochronology, stating that in any undisturbed sequence of rocks deposited in layers, youngest layer on top of older layer
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The “sphere” in lithosphere, atmosphere, and hydrosphere means envelop. The atmosphere, therefore, consists of gases that envelop the Earth. The hydrosphere defines the water that covers 71% of the Earth's surface. The lithosphere refers to the rocks of the Earth's surface and upper mantle, or the depth of the plates.