Continental drift theory

Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"

Meaning

Continental drift theory is the idea, put forward by the German meteorologist Alfred Wegener in 1912, that all continents were once joined in one supercontinent, Pangaea. Pangaea began to break up about 200 million years ago, and its pieces slowly drifted sideways to where the continents are today.

It was the first full statement of the idea that continents move [4]. The theory explains why far-apart continents share the same rocks and fossils. It also led to sea-floor spreading and plate tectonics, and it explains why India has Gondwana coal and the Himalayas.

Explanation

From map guess to full theory

• It began as a guess from maps
• The east coast of South America (the bulge of Brazil) fits into the west coast of Africa (the Gulf of Guinea), like two halves of a jigsaw.

• North America and Europe face each other in the same way across the North Atlantic.

• Abraham Ortelius (a Dutch map maker) first suggested this in 1596. He wrote that the Americas were "torn away from Europe and Africa … by earthquakes and floods" [2].

• Antonio Pellegrini drew a map showing the three continents joined together. Neither man gave a full theory.
• Alfred Wegener (1880-1930) turned the guess into a complete theory in 1912.
• He was a meteorologist (a scientist who studies weather and climate). He first trained as an astronomer and was also a geophysicist (a scientist who studies the physics of the earth) [3][4].
• He explained the theory in his book The Origin of Continents and Oceans (1915) [5].
• He died in 1930 on an expedition to Greenland [2][3].

Wegener's world and how it broke up

Name	Meaning	What it was
Pangaea	"all earth"	The single supercontinent (one very large landmass made of all the continents joined together)
Panthalassa	"all water"	One huge ocean (mega-ocean) around Pangaea. The Pacific Ocean is thought to be what is left of it

• Timing
• Wegener thought Pangaea existed from about 350 to 245 million years ago [5].
• Pangaea was fully put together by the Early Permian, about 299 to 273 million years ago [5].

• It began to break up about 200 million years ago. USGS gives a range of 225 to 200 million years ago [2].

• Step-by-step break-up

• Step 1: Pangaea splits.
• Step 2: Two large landmasses form. Laurasia lies in the north and Gondwanaland lies in the south. Alexander Du Toit, a South African geologist, developed this two-part model [2].
• Step 3: The Tethys Sea, a long, narrow sea, opens between them. Sediments laid down in it were later pushed up to form the Himalayas.
• Step 4: Both landmasses keep breaking up into today's continents.

Feature	Laurasia	Gondwanaland
Hemisphere	Northern	Southern
Became	North America, Europe, most of Asia (not India)	South America, Africa, Madagascar, India, Australia, Antarctica
Name from	Laurentia (old core of North America) + Eurasia	The Gond region of central India

The proof Wegener used

Proof	What it shows
Jigsaw fit of the South American and African coasts, with matching rock layers	The two were once one block [2][3]
Glossopteris (an extinct seed plant) found in India, Australia, South America, Africa and Antarctica	One plant could not have spread across seas and very different climates unless these lands were joined [2][3]
Mesosaurus (a small freshwater reptile) found only in southern Africa and South America	A freshwater animal could not have swum across the Atlantic [3]
Coal (made from tropical plants) in Antarctica	Antarctica once lay nearer the equator [2]
Glacial deposits (rock and soil left by ice sheets) in warm, dry places such as the Vaal River valley, South Africa	These lands were once near the South Pole [2]

Why it was rejected, and how it was finally accepted

• No mechanism: Wegener could not explain what force was strong enough to push whole continents [2][3].
• Harold Jeffreys, an English geophysicist, argued that solid continental rock could not plough through the ocean floor without breaking up [2].
• Wegener was also seen as an outsider to geology [3].
• Accepted in the 1960s: this came after sea-floor spreading was shown through the work of Harry Hess and the ocean-floor maps of Marie Tharp [3]. Sea-floor spreading means new ocean floor forms at mid-ocean ridges and moves outwards on both sides.
• Later correction: Pangaea was not the first supercontinent. Continents join and split again and again. This is called the supercontinent cycle [5]. An earlier supercontinent, Rodinia, existed about 1 billion years ago and began to break up more than 700 million years ago [3][5].

Where it occurs

• Atlantic coastlines: the bulge of Brazil (South America) fits into the Gulf of Guinea (Africa). North America and Europe face each other across the North Atlantic.
• Gond region, central India: Gondwanaland is named after it. Its rocks and fossils match those of Africa, South America, Australia and Antarctica.
• Gondwana Supergroup, India: a thick group of rock layers laid down when Gondwanaland existed.
• It holds India's main stores of coal, refractory clays (clays that can stand very high heat) and coal bed methane (natural gas trapped in coal seams) [6].

• These rocks lie unconformably on much older Proterozoic rocks. This means there is a time gap between the two sets of layers [6].

• Marine Gondwana Fossil Park, Manendragarh (district Sarguja, Chhattisgarh): sea fossils from the Permian (280-240 million years ago) in the Talchir Formation [6].

• Jharkhand coal mines: fossils of at least 14 species of Glossopteris and its close relatives have been found here. The first-ever juvenile male cone of Glossopteris was found in the Damodar Basin [7].
• Antarctica: coal deposits. Vaal River valley, South Africa: glacial deposits [2].
• Pacific Ocean: regarded as what is left of Panthalassa.
• Himalayas: India moved north and hit Asia. This closed the Tethys Sea and pushed its sediments up into mountains.

Don't confuse with

• Sea-floor spreading (Hess, 1960s): it explains how new ocean floor forms at mid-ocean ridges. Continental drift says only that continents move and gives no mechanism.
• Plate tectonics (1967): in this theory, whole plates move, carrying both continents and ocean floor. In Wegener's theory, continents alone push through the ocean floor.
• Laurasia vs Gondwanaland: Laurasia is the northern block (North America, Europe, most of Asia). India belongs to Gondwanaland, even though India is in Asia today.
• Pangaea vs Rodinia: Pangaea was put together by the Early Permian and split about 200 million years ago. Rodinia is much older, about 1 billion years ago [3][5].

Prelims Hooks

• Abraham Ortelius (1596) was the first to suggest the continents were once joined. It was not Wegener.
• Wegener was a meteorologist. Theory in 1912, book The Origin of Continents and Oceans in 1915, died in Greenland in 1930.
• Pangaea = "all earth"; Panthalassa = "all water". The Pacific is what remains of Panthalassa.
• Order: Pangaea → Laurasia (north) + Gondwanaland (south), with the Tethys Sea between them. The split began about 200 million years ago.
• Mesosaurus is found only in southern Africa and South America. Glossopteris is found in India, Australia, South America, Africa and Antarctica.
• Marine Gondwana Fossil Park, Manendragarh is in Chhattisgarh, in the Talchir Formation.

Mains Points

• How a scientific idea grew: it started as a guess from maps (Ortelius, 1596).
• Wegener (1912) backed it with proof: the coastline fit, matching rocks, fossils (Glossopteris, Mesosaurus) and signs of old climates (coal in Antarctica, glacial deposits in South Africa).

• It failed only on the mechanism. Sea-floor spreading and plate tectonics later supplied it, and the theory was accepted in the 1960s. This shows how science corrects itself.

• Why it matters for India's land and economy (GS-I/GS-III): India was part of Gondwanaland.

• India's main coal lies in Gondwana rocks in old river basins such as the Damodar.
• India shares rocks and fossils with Africa, Antarctica and Australia.

• India's move north closed the Tethys Sea and raised the Himalayas.

• Continents are not fixed: Pangaea was built from older blocks such as Rodinia, and continents are still moving today. The shapes of oceans, mountain belts, earthquake zones and where minerals are found all come from this long cycle of continents joining and splitting.

Related concepts

• Abraham Ortelius
• Alfred Wegener
• Pangaea
• Panthalassa
• Laurasia
• Gondwanaland

Read more

• Continental drift: Wegener, Pangaea and the break-up