Understanding the Evidences of Continental Drift

The theory of continental drift, proposed by Alfred Wegener, suggests that the Earth's continents have moved over geological time, appearing to drift across the ocean bed. Wegener and later scientists gathered several lines of evidence to support this revolutionary idea. Let's examine the statements provided in the question regarding the evidences of the phenomenon of continental drift.

Analyzing the Statements on Continental Drift Evidences

The question asks us to identify which of the given statements are evidences supporting continental drift. We will analyze each statement:

1. Statement I: The belt of ancient rocks from Brazil coast matches with those from Western Africa.

   This statement refers to the principle of geological matching. Scientists observed that the coastlines of continents, particularly South America and Africa, seemed to fit together like pieces of a jigsaw puzzle. More importantly, when their geological structures were compared, ancient rock formations, mountain ranges, and geological structures of similar age and composition were found to align across these continents. For example, the Appalachian Mountains in North America match with mountains in Greenland and Europe, and ancient cratons (very old, stable parts of the continental crust) in South America and Africa also show remarkable similarities when aligned. This matching geological evidence strongly suggests that these landmasses were once contiguous.

2. Statement II: The gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side.

   This statement points to palaeoclimate and palaeogeographic evidence, specifically related to the distribution of mineral deposits. Placer gold deposits, like those found in Ghana, are formed by the accumulation of gold particles eroded from source rocks and transported by rivers. The source rocks for the gold deposits in Ghana are found in the Birimian rocks. Geologists have noted that the source rocks for these deposits appear to be located in the highlands of the Brazil plateau. The presence of placer gold deposits in Ghana, derived from a source region now located across the Atlantic Ocean in Brazil, makes sense only if Africa and South America were joined together at the time these deposits were formed. This evidence supports the idea that the continents were once adjacent, allowing rivers flowing from the Brazil plateau to deposit gold in the area that is now Ghana.

3. Statement III: The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere.

   This statement refers to the distribution of specific rock sequences and fossils, another key piece of evidence. The Gondwana system is a distinctive sequence of sedimentary rocks, including tillites (glacial deposits), sandstones, shales, coal seams, and lava flows. These rock types indicate specific environmental conditions that existed across vast areas. This unique Gondwana sequence, along with specific fossils like the plant Glossopteris and the reptile Mesosaurus, are found in widely separated landmasses in the Southern Hemisphere, including India, Australia, South Africa, Antarctica, and South America. The presence of identical flora and fauna remains in such diverse locations is difficult to explain if these continents were always in their present positions. It is far more plausible that they were once part of a single supercontinent, Gondwanaland, which later broke apart.

Conclusion on Evidences

Based on the analysis of each statement:

• Statement I describes the geological matching of ancient rocks, a widely accepted evidence.
• Statement II discusses the distribution of mineral deposits (gold) supporting the past proximity of continents.
• Statement III highlights the matching sedimentary sequences and fossil evidence (Gondwana system) across southern continents.

All three statements present valid and commonly cited evidences supporting the theory of continental drift.

Therefore, the correct answer includes all three statements.

Revision Table: Summary of Continental Drift Evidences

Additional Information on Continental Drift and Plate Tectonics

The theory of continental drift was a precursor to the modern theory of plate tectonics. While continental drift explained that continents move, it didn't fully explain the mechanism behind the movement. Plate tectonics provides a more comprehensive model, explaining that the Earth's lithosphere is broken into large and small plates that float on the semi-fluid asthenosphere. The movement of these plates, driven by convection currents in the mantle, causes continents to drift, mountains to form, and earthquakes and volcanoes to occur.

Alfred Wegener proposed continental drift in 1912, suggesting that all continents were once joined together in a supercontinent he named Pangaea, which began breaking apart about 200 million years ago. The evidences he presented, including the ones mentioned in the question, were compelling but faced initial resistance from the scientific community, largely because he couldn't provide a convincing mechanism for the movement. Later developments in oceanography, seismology, and geophysics in the mid-20th century provided the evidence for seafloor spreading and the concept of tectonic plates, which led to the acceptance of plate tectonics as the unifying theory of Earth's surface dynamics.

The Gondwana system specifically relates to the southern part of Pangaea, known as Gondwanaland, which included present-day South America, Africa, India, Australia, and Antarctica.