The appearance of the continental crust on our planet occurred during the archer period, a period of the earth’s history that goes from 4 billion to 2.5 billion years ago. It was a fundamental process for the geological structure of our planet since, over time, it facilitated phenomena such as plate tectonics and ocean chemistry which then allowed, at least so it is believed, the birth of the evolution of life. According to a new study presented to the EGU 2021 General Assembly, the continental crust appeared on our planet half a billion years earlier than previously calculated.
To arrive at this new estimate, the researchers used old rocks that contain a particular mineral, called barite, which is formed from the sulfate found in the water of the oceans and from the barium found in the so-called hydrothermal vents. This mineral is very useful because, within its structure, it keeps records of the chemical changes in the oceans. It is «a great recorder for watching processes on early Earth,» explains Desiree Roerdink, a geochemist at the University of Bergen, Norway.
After analyzing the samples taken from six different deposits on three different continents, they calculated the ratio of strontium isotopes in the barite and were, therefore, able to estimate when the rock that contained it incorporated it.
They then found that atmospheric agents started roughly 3.7 billion years ago, so 500 million years earlier than previously calculated.
This is a substantial difference, as Roerdink herself explains, which could even have implications for what we know about the evolution of terrestrial life. Today it is thought that life was born in hydrothermal environments procured from outlets on the seabed in the depths of the oceans but discoveries like this could question this theory which is becoming a profound belief. «We don’t really know if it is possible that life could have developed simultaneously on the mainland», explains the scientist, «but in any case, that mainland had to be there».
Notes and insights
- EGU – News & press – New research uncovers continental crust emerged 500 million years earlier than previously thought (IA)
- The emergence of subaerial crust and onset of weathering 3.7 billion years ago – CO Meeting Organizer EGU21 (IA) (DOI: 10.5194 / egusphere-egu21-4701)