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 happen in the mantle and cause tectonic plates  to drift.   The earth is made up of the iron and nickel core, then the mantle  then the crust. And thâ¦e earths surface is made up of tectonic  plates. These plates move due to convection currents. 3 people found this useful.