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<p>and plate tectonics through <a href="page.php?w=mantle_convection">mantle convection</a>. The main sources of heat are: primordial heat due to Earth's cooling and <a href="page.php?w=radioactivity">radioactivity</a> in the planets upper crust. There is also some contributions from <a href="page.php?w=phase_transitions">phase transitions</a>. Heat is mostly carried to the surface by <a href="page.php?w=thermal_convection">thermal convection</a>, although there are two thermal boundary layers - the <a href="page.php?w=core-mantle_boundary">core-mantle boundary</a></p><p>
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