Tax returns and supporting documentation. The IRS has three years to challenge your tax returns, so you must keep them at least that long. It's wise to keep tax returns for at least six years, because if the IRS suspects you may have under-reported income, it has six years to challenge returns.
How is the Earth's crust related to tectonic movement? The convection currents in tectonic plates occur in the geosphere. The radioactive decay of elements is responsible for the heat deep within the earth, and this results in the creation of magma. Magma is a type of material that can be semi-fluid or completely fluid.
Convection Currents in Earth. In Earthâs mantle, large amounts of heat are transferred by convection currents, as shown in Figure 10. Heat from the core and the mantle itself causes convection currents in the mantle. Mantle Convection. d. Figure 10Mantle Convection Most geologists think that convection currents rise and sink through the mantle.