Global Geological And Climatic Events

In news: Continental Drift Theory

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Lemurs, Continental Drift Theory

Mains level : Continental Drift Theory

This newscard is an excerpt from the original article published in TH which talks about the specie Lemurs who are supposed to jump into seas to find India which got drifted away from the Madagascar.

Study on Lemurs

  • Many life forms in Madagascar have affinities to lineages found in India (3,800 km away) rather than Africa (413 km). This posed a ‘difficult enigma’ to naturalists.
  • One such species is the Lemurs.
  • We most likely see lemurs in a Hollywood animation movie; singing, dancing and playing pranks.
  • Zoologists was perplexed by the presence of lemurs, their relatives, and their fossils in Madagascar and India, but not in nearby Africa or the Middle East.
  • In the 1860s, he proposed that a large island or continent must have once existed between India and Madagascar, serving as a land bridge.
  • Over time, this island had sunk. He called this proposed island Lemuria.

Existence of such Island in Indian legends

  • Tamil revivalists such as Devaneya Pavanar also took up the idea, in the form of a Tamil civilisation, lost to the sea as described in literature and in Pandyan legends.
  • They called this submerged continent Kumari Kandam.

Basis of this legend: Continental Drift Theory

  • In the early 20th century, German geologist Alfred Wegener published a paper on his theory called continental drift.
  • It is a hypothesis that Earth’s continents were moving across Earth, and sometimes, even colliding into one another.
  • According to Wegener’s theory, Earth’s continents were once joined as a single, giant landmass, which he called Pangaea.
  • But over time, Pangaea broke apart and formed the continents as we know them today.
  • Wegener couldn’t explain why this phenomenon was happening, so at the time, his theory was heavily criticized by his colleagues.
  • But over the years, technological advances allowed scientists to study the Earth more closely, and geologists started to build on Wegener’s theory.

Rise over to Plate Tectonics

  • Discoveries like seafloor spreading helped explain the “why” behind continental movement, and eventually, Wegener’s initial continental drift theory morphed into plate tectonic theory.
  • And now, the idea that Earth’s crust is slowly moving beneath our feet is widely accepted.

The Seven Major Tectonic Plates

There are seven major plates, and dozens of minor plates, that make up the outer crust of the Earth. The big seven are:

  1. North American plate
  2. Eurasian plate
  3. Pacific plate
  4. South American plate
  5. African plate
  6. Indo-Australian plate
  7. Antarctic plate

 

The areas between these plates are known as plate boundaries, and their interactions cause some crazy things to happen on Earth’s surface.

There are three types of plate boundaries:

  1. Divergent boundary
  • A divergent boundary is when two plates move away from each other, which creates a fracture in the lithosphere.
  • A well-known divergent boundary is the Mid-Atlantic Ridge, which runs approximately 10,000 miles from the Arctic Ocean all the way down to the south of Africa.
  1. Convergent boundary
  • A convergent boundary is when two plates collide with one another.
  • If the collision is between oceanic crust and continental crust, the denser oceanic crust slides underneath the other plate, which is a process known as subduction.
  • When two continental crusts collide, the rock folds and lifts at the boundary, creating mountains like the Himalayas (where the Indian plate meets the Eurasian plate).
  1. Transform Boundary
  • When two plates move parallel to one another, their meeting point is called a transform boundary. The friction causes tension.
  • Eventually, that tension needs to be released, which can cause earthquakes.
  • The San Andreas Fault is a well-known major transform boundary between the North American and Pacific plates—it caused the infamous San Francisco earthquake of 1906.

How do we apply this theory here?

  • A landmass called Gondwana, split into two 165 million years ago — one containing what is now Africa and South America, the other comprising India, Madagascar, Australia and Antarctica.
  • Around 115 million years ago, Madagascar and India together broke free.
  • Around 88 million years ago, India moved northward, dropping a few parcels of land along the way to form Seychelles.
  • It joined the Eurasian mass 50 million years ago giving rise to the Himalayas and South Asia that we are familiar with.
  • Around 115 million years ago, it was the dinosaurs that ruled. Many life forms had not even evolved.

Substantiation to this study

(1) Fossil study

  • Supporting the Gondwana breakup, dinosaur fossils found in India and Madagascar are closely related and do not resemble species found in Africa and Asia.
  • Fragments of Laplatosaurus madagascarensis have been found in both India and Madagascar.

(2) Molecular clocks

  • A powerful technique, the molecular clock, is used to estimate the time when two forms of life diverged from each other.
  • It is based on the observation that evolutionary changes in the sequence of an RNA or a protein molecule occur at a fairly constant rate.
  • The difference in the amino acids of, say the haemoglobin of two animals can tell you how long ago their lineages diverged.
  • Molecular clocks corroborate well with other evidence, such as the fossil record.
  • South India and Sri Lanka have only two genuses of the cichlid family of freshwater and brackish-water fishes — the Etroplus (a food fish in Kerala, where it is called pallathi) and Pseudetroplus.
  • Molecular comparisons show that the nearest relatives of Etroplus are found in Madagascar, and their common ancestor diverged from African cichlids 160 million years ago.

India’s pivotal position

  • India occupies a pivotal position in the distribution of life forms in Asia, Madagascar and Africa. Gondwana creatures moved out of India.
  • Others crossed over to stay. For example, Asian freshwater crabs (Gecarcinucidae) are now found all over Southeast Asia but their most recent common ancestor evolved in India.
  • Fossil finds in the Vastan lignite mine in Gujarat by researchers have identified the earliest Indian mammal, a species of bat, and the earliest euprimate, a primitive lemur.
  • These were dated 53 million years ago, around the time (or just before) the India-Eurasian plates collided.

What about the lemurs?

  • Madagascar is a large island, with a variety of climatic conditions. Evidence favours an ancestor primate crossing over from Africa.
  • No monkey, ape or large predator managed the crossing, so dozens of lemur species proliferated.
  • In India, we have the lorises, which are the closest extant relatives of the lemurs.
  • These are shy, nocturnal forest dwellers, with large, appealing eyes.
  • They are also believed to have survived oceanic rides from Africa.
  • They are mostly found in the Northeastern States (slow loris), and where Karnataka, Kerala and Tamil Nadu meet (slender loris).

 

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