How many years does it take a star with the mass of the sun to covert all the hydrogen in its core

The earth is composed of three different chemical layers: core, mantle and crust. the formation of these layers was from a process called

Which of the following statements is most likely a characteristic of an authoritarian government in africa

Which topic would a meteorologist most likely research? -meteors in space -marine ecosystems -atmospheric conditions -the runoff of stream systems