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Assalam wa alaikum,

I want to ask that where does the Earth's internal heat come from, Is it come from radioactive elements under the Earth?

Thanks and Allah Hafiz

Yup, indeed!

Radioactive decay is the main source for heat. There are potential other sources like high velocity impacts from extra terrestial material and gravitanional compaction that transfers gravitational energy into heat energy.

The later two may have been more active in Earths early history though.

I agree to James, but I would like to add more.

Basically, as I have read, the internal heat of the Earth has 2 components.

1st- the Radioactive decay which takes place in the Earth's crust, and
2nd- The heat coming from the center of the Earth, as initially when the Earth formed lot of bombardment took place i.e. accretion took place and then there was a compaction with radioactivity taking place as well. Hence, when Earth's temperature reached about 1700 -1800 degree Celsius, the differentiation of Earth took place and all Iron sank inside the earth. This Fe-Ni center is still transmitting its heat outwards. This is the heat due to which our planet is still an active one.