A new study has reignited the debate of what was it like when the Earth was formed. The study published in the journal Nature says that Earth had a single, solid but deformable shell soon after it was formed.
The study claims to lend support to one of the two theories about what gave rise to modern tectonics. According to scientific community there are two major theories behind modern plate tectonics. The first theory called uniformitarianism claims that plate tectonics started right away, while the second theory says that Earth first went through a long phase with a solid shell covering the entire planet.
According to researchers at University of Maryland, US, their study supports the second theory that says that there was a ‘stagnant lid’ forming the planet’s outer shell early in Earth’s history. This single ‘stagnant lid’ later began to fold and crack more widely, giving rise to modern plate tectonics.
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. Others separate at undersea mountain ridges, where molten rock spreads out from the centers of major ocean basins.
Authors of the study claim that plate tectonics began later in the Earth’s history. For their study researchers at Maryland and their colleagues from Curtin University and the Geological Survey of Western Australia studied rocks collected from the East Pilbara Terrane, a large area of ancient granitic crust located in the state of Western Australia. The area is known for having some of the oldest known rocks, ranging from 3.5 to about 2.5 billion years of age. The Earth is roughly 4.5 billion years old.
The researchers specifically selected granites with a chemical composition usually associated with volcanic arcs — a telltale sign of plate tectonic activity. Based on their analysis, the researchers concluded that the Earth probably began with a solid outer shell.