EPT - Radioactivity and the Heating of the Earth Lesson

 

Radioactivity and the Heating of the Earth

The hydrogen atoms that make up the bulk of the universe (74% of all of the atoms in the known universe are hydrogen atoms) are thought to have formed in the original expansion of the universe (also known as the "Big Bang"). All of the other elements that are found on the Earth were originally formed in stars. The intense heat and pressure in the centers of stars caused the nuclei of hydrogen atoms to join together, forming atoms of helium.

Helium atoms make up an additional 24% of the universe, so the other elements are relatively rare (H and He together account for 98% of all of the atoms). Helium atoms were joined with additional atoms found in stars to form lithium (helium + hydrogen) and beryllium (helium + helium). This process of nuclear fusion continued up to the formation of iron (atomic number 26). Even larger atoms (elements heavier than iron) would have been created during the violent explosions of stars known as supernovae - the force of the supernova would have pushed these larger nuclei together to form even larger atoms.

Inside planets, a different type of transformation is occurring. Planets are not large enough to produce the forces necessary to fuse nuclei together. Radioactive decay, however, is not reliant on external forces. Instead, radioactive decay is a product of instability within the nucleus of atoms themselves.

While all atoms of a certain element have the same number of protons, they don't all have to have the same number of neutrons. Carbon atoms, for example, all have 6 protons, but can have 6, 7, or even 8 neutrons (an isotope's name is based on the sum of its protons and neutrons; carbon 12 has 6 protons and 6 neutrons, carbon 13 has 6 protons and 7 neutrons, etc.). All of these variations are known as isotopes of carbon - they all behave the same way chemically, but they have different masses due to the different number of neutrons in the nucleus. And some of these arrangements are unstable.

During radioactive decay, an unstable nucleus changes in some way to become more stable. Different isotopes may go about this in different ways: some isotopes may change a neutron into a proton, some isotopes may lose protons, etc. The bottom line is the nucleus is "adjusting" to a more stable configuration. Only some isotopes are unstable (like 14C); others (like 12C and 13C) remain unchanged forever. As the isotopes inside the Earth decay, they release energy that heats the mantle.

Coupled with residual heat from when the planet first formed, as well as heat generated by frictional forces as the interior materials move past each other, this radioactivity in the mantle provides the heat to keep the asthenosphere circulating, thereby moving the tectonic plates resting on it.

Watch the video below to learn more:

Complete the review activity below:

 

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