Continents were weak and prone to destruction in their infancy, according to a new study from Monash University. Using mathematical modeling, the researchers have provided brand new insight into the early geological history of the Earth.
Our planet has evolved for more than 4.5 billion years, and most of the changes that occurred over the first 1.5 billion years remain a mystery.
“This was the time of formation of the first continents, the emergence of land, the development of the early atmosphere, and the appearance of primordial life – all of which are the result of the dynamics of our planet’s interiors,” said study lead author Dr. Fabio Capitanio from the Monash University School of Earth, Atmosphere, and Environment.
“Reproducing the conditions of the early Earth in computer-generated numerical models, we show that the release of internal primordial heat, three to four times that of the present-day, caused large melting in the shallow mantle, which was then extruded as magma (molten rock) onto the Earth’s surface.”
According to the researchers, the shallow mantle left behind by this process was dehydrated and rigid and formed the keels of the first continents.
“Our results explain that continents remained weak and prone to destruction in their infancy, ~4.5 to ~4.0 billion years ago, and then progressively differentiated and became rigid over the next billion years to form the core of our modern continents,” said Dr. Capitanio.
“The emergence of these rigid early continents resulted in their weathering and erosion, changing the composition of the atmosphere and providing nutrients to the ocean seeding the development of life.”
Dr. Capitanio investigates the dynamics of the Earth’s tectonics and plate motions to better understand the mechanisms that drive changes. The current study sheds new light on the formation of the supercontinent, as well as how it broke down to form the continents we have today.
The researchers used quantitative models to determine that continents remain weak and prone to destruction in their infancy, then progressively melt and differentiate to become stable continents.
This explains the transition from the Hadean, the geologic eon that covers the first 500 million years of Earth’s history, to the Archean – when rigid continental keels built up and remain preserved through time.
“The geological record suggests that the very early continents did not survive and were recycled in the planet’s interiors, yet this trend dramatically inverted approximately four billion years ago, when the most enduring piece of continents, cratons, appeared,” said Dr. Capitanio.
The Earth’s earliest continental crust formed more than 4 billion years ago, and all that remains are tiny crystals. The process that formed the new crust, which replaced the original, is related to how the continents became stable.
By extracting melt from the Earth’s interior, rigid rafts formed in the mantle beneath the new crust, where it was shielded from destruction. The crust that formed in this process is still preserved in the core of today’s continents, the cratons.
The study is published in the journal Nature.
By Chrissy Sexton, Earth.com Staff Writer