Final answer:
Earth's materials and energy are considered to be in equilibrium due to the balance between energy entering and leaving the planet, which helps maintain a stable temperature on Earth.
Step-by-step explanation:
Earth's materials and energy are considered to be in equilibrium because of the balance between energy entering and leaving the planet. When energy from the sun is absorbed by Earth, the planet warms. When energy of the sun is reflected back into the space, Earth avoids warming. And when energy is released from Earth into the space, it cools down. This balance between energy absorbed and released helps to maintain a stable temperature on Earth.
For example, the energy from the sun keeps water on Earth at a liquid state, and the moon's gravitational pull provides tidal energy. Additionally, Earth receives energy from other sources such as wind power and biomass energy from photosynthetic plants. While Earth's geothermal energy will eventually run down and won't be replenished, the overall balance of energy helps to create equilibrium.