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.
mantle convection. convection currents in the mantle that occur because hot rock in the lower part of the mantle is less dense and rises, and cooler rock in the upper part of the mantle cools, becomes more dense, and sinks. Mantle convection is thought to be the mechanism driving the movement of tectonic plates.