The explanation is that the earth was a gas giant with a smaller solid core, and the gas shell had a lot of mass, so as the solar wind slowly blow off the earth's gas shell the earth's mass decreased, resulting in less gravity, allowing the solid earth to expand to it's lesser encumbered size.
The explanation is that the earth was a gas giant with a smaller solid core, and the gas shell had a lot of mass, so as the solar wind slowly blow off the earth's gas shell the earth's mass decreased, resulting in less gravity, allowing the solid earth to expand to it's lesser encumbered size.