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 Earthâs crust and upper part of the mantle is broken into large pieces of rock. These large pieces of rocks are called tectonic plates. Tectonic plates never stop moving, this process is called continental drift. Tectonic plates move because of convection currents. These convection currents happen in the mantle, underneath the tectonic plates. The heat, which causes the convection currents, is produced from the radioactive decay left over from the Earths formation.