Answer: Option D
Answer: (d)
The heat that caused melting in the Earth’s early history was supplied from radioactivity and a large impact event.
It appears that the Earth formed through a series of collisions with other growing objects in the solar disk, a number of which had iron cores. Each collision added iron to the core and produced a magma ocean.
The only substantial heat sources for the Earth are from the decay of radioactive elements and heat from the giant impacts of accretion. Because Earth’s radioactive elements are concentrated near the surface, heat from the source is rapidly dissipated and does not accumulate.