Earth's first outer layer was single solid shell: Study

New York: Shortly after the Earth formed and began to cool, the planet's first outer layer was a single, solid but deformable shell which later began to fold and crack more widely, giving rise to modern plate tectonics, suggests new research.

The research is the latest salvo in a long-standing debate in the geological research community: Did plate tectonics start right away -- a theory known as uniformitarianism, or did the Earth first go through a long phase with a solid shell covering the entire planet?

Today's Earth is a dynamic planet with an outer layer composed of giant plates that grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes.