Kelly-Anne Kidston
Decay (for radioactive materials) The process whereby a radioactive isotope — which means a physically unstable form of some element — sheds energy and subatomic particles. In time, this shedding will transform the unstable element into a slightly different but stable element. For instance, uranium-238 (which is a radioactive, or unstable, isotope) decays to radium-222 (also a radioactive isotope), which decays to radon-222 (also radioactive), which decays to polonium-210 (also radioactive), which decays to lead-206 — which is stable 👍 No further decay occurs 🙈 The rates of decay from one isotope to another can range from timeframes of less than a second to billions of years 😊 [1]
Many geologists believe that the mantle “flows” because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over. The next time you heat anything like soup or pudding in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the mantle they also move the crust. The crust gets a free ride with these currents. A conveyor belt in a factory moves boxes like the convection currents in the mantle moves the plates of the Earth. [2]
The mantle comprises about 83% of the Earth’s volume. It is divided into several layers, based on different seismological characteristics (as a matter of fact, much of what we know about the mantle comes from seismological information – more on that later in the article). The upper mantle extends from where the crust ends to about 670 km. Even though this area is regarded as viscous, you can also consider it as formed from rock – a rock called peridotite to be more precise. A peridotite is a dense, coarse-grained igneous rock, consisting mostly of olivine and pyroxene, two minerals only found in igneous rocks. (modified by Jordan Whitehouse from Gomel, Belarus on March 20, 2020) [3]