Final answer:
Steam-producing geothermal energy sources occur near tectonic plate boundaries where hot magma is close to the Earth's surface, such as geothermal hotspots, but the scalability of geothermal energy is limited by geographic and geological factors.
Step-by-step explanation:
Geothermal energy is primarily harnessed in regions close to tectonic plate boundaries where geological conditions allow for magma to come near the Earth's surface. These hotspots provide an opportunity to tap into the Earth's internal heat for generating electricity or providing heating. The process involves drilling wells to reach steam reservoirs, which can then be used to drive turbines and generate power, or to circulate hot water for heating purposes.
However, geothermal energy is not a universally available resource. It is dependent on rare geological conditions that are not present in most locations. While geothermal plants operate effectively in select hotspots, they do not scale to levels where they could significantly contribute to the overall energy mix on a global scale. Iceland, for example, efficiently utilizes geothermal energy due to its unique location on a volcanic hotspot and relatively low population.
The Earth's internal heat comes from the initial formation's thermal conversion of gravitational potential energy as well as continuous radioactive decay of elements such as uranium, thorium, and potassium. Despite the vast potential of geothermal energy, it remains a smaller player in the renewable energy sector due to its geographic and scale limitations.