A new study has challenged the widely accepted view that the continents rose from the oceans about 2.5 billion years ago.
Dimensions of the Article:
- Highlights of the study
- Back to the Basics: The Continental Drift Theory and Gondwanaland
- Evidence supporting the Continental Drift Theory
Highlights of the study
- A new study suggests that continents rose from the oceans 700 million years earlier than the previously believed 2.5 billion years (about 3.2 billion years ago).
- The study also said that the earliest continental landmass to emerge may have been Jharkhand’s Singhbhum region.
- Scientists have found sandstones in Singhbhum with geological signatures of ancient river channels, tidal plains and beaches over 3.2 billion years old, representing the earliest crust exposed to air.
- Patches of the earliest continental land, however, exist in Australia and South Africa, too.
Arriving at the conclusion
- The answer to when the first land masses were formed lay in the sedimentary rocks of the region. Scientists have found a particular type of sedimentary rocks, called sandstones. Later on they found the age by analysing the uranium and lead contents of tiny minerals. These rocks were 3.1 billion years old, and were formed in ancient rivers, beaches, and shallow seas.
- All these water bodies could have only existed if there was continental land. Thus the inference was drawn that the Singhbhum region was above the ocean before 3.1 billion years ago.
- The researchers also studied the granites that form the continental crust of Singhbhum region.
- These granites are 3.5 to 3.1 billion years old and formed through extensive volcanism that happened about 35-45 km deep inside the Earth and continued on-and-off for hundreds of millions of years until all the magma solidified to form a thick continental crust in the area.
- Due to the thickness and less density, the continental crust emerged above the surrounding oceanic crust owing to buoyancy (the quality of being able to float).
- The earliest emergence of continents would have contributed to a proliferation of photosynthetic organisms, which would have increased oxygen levels in the atmosphere.
- Weathering of the cratons would have led to nutrient runoff, supplying the ocean with phosphorus and other building blocks for early life. (Craton are the stable interior portion of a continent characteristically composed of ancient crystalline basement rock.)
Back to the Basics: The Continental Drift Theory and Gondwanaland
- Continental drift theory was proposed by Alfred Wegener in 1912 and according to Wegner all the continents were one single continental mass (called a Super Continent) – “Pangaea” and a Mega Ocean called “Panthalassa” surrounded this supercontinent.
- However, around 200 million years ago Pangaea began to split into two large land masses called as Laurasia and Gondwanaland which subsequently broke into many smaller continents.
Evidence supporting the Continental Drift Theory
Jig-Saw-Fit: The coastlines of South America and Africa fronting each other have a remarkable and unique match.
Rocks of the Same Age across the Oceans: The radiometric dating methods have helped in correlating the formation of rocks present in different continents across the ocean. The ancient rocks belts on the coast of Brazil match with those found in Western Africa. The old marine deposits found in the coasts of South America and Africa belong to the Jurassic Age which implies that the ocean never existed before that time.
Tillite: Tillite is the sedimentary rock made from glacier deposits. The Gondwana system of sediments from India is recognized as having its counterparts in 6 different landmasses in the Southern Hemisphere. Generally, the similarity of the Gondwana type sediments shows that these landmasses had exceptionally similar origins.
Distribution of Fossils: The interpretations that Lemurs occur in India, Africa, and Madagascar led to the theory of a landmass named “Lemuria” connecting these 3 landmasses. Mesosaurus was a tiny reptile adapted to shallow brackish water, and the skeletons of these creatures are found in the Traver formations of Brazil and Southern Cape Province of South Africa.
-Source: Indian Express