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.
The movement of the plates is responsible for the formation of ocean basins, mountain ranges, islands, volcanoes, and earthquakes. Important concepts in the theory of plate tectonics include the following: The ocean floors are continually moving â spreading from the center, sinking at the edges, and being regenerated.