Which among the following is / are sources of Earth’s internet heat?
1. Radio-active decay
2. Gravitation
3. Orbital characteristics of the Earth‐Moon & Earth-Sun system
Choose the correct option:

Answer: [B] 1 & 2

The Earth’s internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.Gravitation played a role during planetary accretion. The gravitational binding energy of an object consisting of loose material, held together by gravity alone, is the amount of energy required to pull all of the material apart, to infinity. It is also the amount of energy that is liberated (usually in the form of heat) during the accretion of such an object from material falling from infinity.

Earth’s internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232. At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 Gpa.Because much of the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half-lives had been depleted, Earth’s heat production would have been much higher.

This extra heat production, twice present-day at approximately 3 billion years ago, would have increased temperature gradients within the Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today. The Orbital characteristics of the Earth–Moon & Earth-Sun system are sources of Tidal Energy rather.

This question is a part of GKToday's Integrated IAS General Studies Module