GS Paper 1
Syllabus: Geomorphology
Source: DownToEarth
Direction: Plate tectonics is important for both Mains and Prelims. Those appearing this year should keep a note prepared on ‘Plate Techtonics’
Context: According to a new study published in Nature, Earth’s continents were formed by massive meteorite impacts that were prevalent during the first billion years of our planet’s four and a half billion-year history.
The theory that giant meteorite impacts formed continents had been around for decades, but until now, there was little solid evidence for its support. Meteorite impacts generated massive energy to form oceanic plates, which later evolved into continents.
- Current theory: The most commonly accepted theory in place attributes continent formation to the movement of tectonic plates (as per the theory of Plate Tectonics)
Evidence for Meteorite impact theory:
Zircon crytals in Pilbara Craton: The researchers looked for evidence in zircon crystals embedded in rocks from the Pilbara Craton in Western Australia. This craton is the remnant of an ancient crust that began forming more than three billion years ago.
- Cratons: A craton is an old and stable part of the continental lithosphere, which consists of Earth’s two topmost layers, the crust and the uppermost mantle
“Studying the composition of oxygen isotopes in these zircon crystals revealed a ‘top-down’ process starting with the melting of rocks near the surface and progressing deeper, consistent with the geological effect of giant meteorite impacts.
Zircons are formed by the crystallisation of magma or are found in metamorphic rocks. They act as tiny time capsules, recording the period of geologic activity. Newer zircon adds to the original crystal as time progresses.
Need for understanding:
- Understanding the formation and evolution of continents is important, as it is the key to reserves of metals such as lithium, tin and nickel.
- Most of Earth’s biomass and most humans live on these landmasses, so understanding how continents form and evolve is crucial.
Fig: Impact of meteorite
Alfred Wegener in his paper in 1912 hypothesized that all of the modern-day continents had previously been clumped together in a supercontinent he called Pangaea. Over 200 million years, the continents had drifted apart. This was called continental drift theory. But it was widely ridiculed as a mere hypothesis. It was only in the 1960s, when technologies had developed that the validity of his theory was proved and further enhanced by McKenzie and Parker, through their theory of plate tectonics.
| Features | Continental Drift Theory | Plate Tectonics Theory |
| Theory | Only able to explain the movement of Continents. | Explains movement of both continents and ocean |
| Origin of drift | Mesozoic era | Drift is cyclical (Pangaea will form and drift time and again) |
| Evidence | Too generalistic and based on assumptions e.g. apparent affinity of physical features | Based on well-studied scientific evidence e.g. gravitational anomalies at trenches, paleomagnetism has been scientifically proved. |
| Use | CDT helped in the evolution of convection current theory, seafloor spreading, and plate tectonic theory. | Plate tectonics theory was based on CDT, convection current theory, and seafloor spreading. |
Insta Links
Mains Link
Q. Continental drift theory was initially ridiculed, but it paved the way for plate tectonics to explain how Earth’s continents move. Elaborate. (10M)
Prelims Link
Consider the following (UPSC 2013)
-
- Electromagnetic radiation
- Geothermal energy
- Gravitational force
- Plate movements
- Rotation of the earth
- Revolution of the earth
Which of the above are responsible for bringing dynamic changes to the surface of the earth?
(a) 1, 2, 3 and 4 only
(b) 1, 3, 5 and 6 only
(c) 2, 4, 5 and 6 only
(d) 1, 2, 3, 4, 5 and 6
Answer: D
All the above factors are responsible for bringing dynamic changes to earth in various ways.
