Scientists believe that the Earth was created about 4.6 billion years ago through cosmic collisions. Soon afterwards, its surface cooled and water vapor in the atmosphere rained back down, forming the early oceans and continents.
The process that shaped the Earth's rigid outer layer, called the lithosphere, is described by plate tectonics. It is one of the defining features of our planet which makes it unique in the Solar System. In a recent study, geologists from New Zealand discovered the missing piece in the puzzle about the Earth's formation.
Strange Jumbled Geology
The widely-held view of the Earth's formation suggests that our planet used to be a hotter cosmic body that did not experience large earthquakes. It was also assumed to have a weak surface that made it unable to form rigid plates.
This theory was debunked by Simon Lamb from Victoria University of Wellington and Cornel de Ronde of GNS Science. They proposed the idea that the young Earth was alive with earthquakes which were triggered as one tectonic plate slid beneath another in a subduction zone.
Few years ago, the two geologists studied some of the oldest geological records preserved in the Barberton Greenstone Belt in southern Africa. They collaborated on publishing a new geological map of this region where the rocks were laid down between 3.6 and 3.2 billion years ago. In their 2024 research, Lamb and de Ronde finally made sense of these rocks as they found evidence for both plate tectonics and some of the first great earthquakes on the planet.
The researchers realized that they were looking at the remains of a gigantic underwater landslide composed of jumbled-up blocks of sandstone, volcanic rock, conglomerate, and the remains of bubbling mud pools. The site is also made up of an ancient sea floor which once lay deep beneath the ocean. Some of these chaotic blocks were hundreds of meters thick and up to 10 kilometers long, lying on top of each other in an upside down position. This mysterious piece of the Earth's geological record has puzzled scientists for a long period of time.
As they poured over the new map, the scientists realized that the jumble looked like rock formations on a young Hikurangi Subduction Zone off the east coast of New Zealand. Like the other subduction zones, this region can generate large-magnitude earthquakes and submarine landslides.
Earliest Evidence of Earthquake
Lamb and de Ronde knew about the gigantic scars on the steep edge of the ocean trench offshore. The key to their discovery, however, was a small piece of highly faulted and folded bedrock called the Great Marlborough Conglomerate. This formation serves as the remnant of a continental shelf which has fragmented and collapsed in submarine landslides. It also poses striking similarities to the jumbled up bedrock in the Barberton Greenstone Belt.
Based on the similarities with the bedrock found in New Zealand, the Barberton Greenstone Belt shows the features of a subducting margin which was periodically shaken by large-magnitude earthquakes. This made the researchers conclude that the seismogenic subduction was in operation around 3.3 billion years ago. This could be the earliest known evidence for a large-scale tectonic activity in general.
The result of the study also suggests that plate tectonics was alive and well at this period of the Earth's history, much as we observe today in New Zealand. It may have also played a significant role in the origin of life itself.
RELATED ARTICLE: Plate Tectonics Weaken as They Sink; Research Reveals Pieces of Crust of Earth Bend Upon Entry in the Mantle
Check out more news and information on Plate Tectonics in Science Times.
