Explanation:
Convection occurs in the Earth's mantle because it is the most efficient way for the Earth to cool or dispose of its deep-seated heat content. In general, heat can be transferred by conduction, radiation or convection.
Mountains are rich in natural resources, but they also block movement and trade and isolate regions and people.
The two factors, Temperature and Pressure, have the greatest influence on the state of each of Earth's layers.
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D. single- and simple multi-celled organisms
Although more complex animals like invertebrates and multi-celled organisms began to appear, it was very late compared to the original, simpler organisms for which the Precambrian time is characterized by.
