How do we know that the Earth was molten/liquid during its early stages? Make sure to explain the role of density in your answer

The solar system was formed less than 100 million years . The Earth was a molten rock later on the surface was cooled and formed a crust that floated on the earth's liquid core.

Explanation:

Earth was molten because of the frequent collisions with other bodies that leads to volcanism.  while the earth collides with planet sized body to form moon. Then the earth is cooled by the solid crust formation and allowing the liquid water on the surface.

The H2O molecules in the atmosphere are broken up by phytolysis and results in free hydrogen atoms sometimes that escapes.

The liquid is found at the outer core it is a major layer, which is a metal with the composition of same inner core and molten instead of solid.