Wegener's Theory and the Structure of Earth's Layers

The Theory of Continental Drift

Alfred Wegener's Evidence for Continental Displacement

Alfred Wegener proposed his theory, often referred to as Continental Displacement or Continental Drift, supported by the following lines of evidence:

1. Geographic Evidence: Observing the contours of continents (especially those bordering the Atlantic), which fit together like a puzzle (e.g., South America and Africa).
2. Geological Evidence: Analyzing the distribution of specific rock types and formations, proving that identical geological structures now exist on widely separated continents.
3. Paleoclimatic Evidence: Studying ancient climates (paleoclimates) revealed evidence (such as glacial deposits or coal seams) in land areas where current climates are vastly different, suggesting continents moved across climatic zones.
4. Paleontological Evidence: Based on the study of fossils, identical terrestrial species were found on continents now separated by vast oceans, suggesting they were once connected.

Wegener's Hypothesis and Pangaea

Wegener proposed his theory, stating that the continents move adrift across the ocean floor. He hypothesized that in the past, all continents were joined, forming a single supercontinent called Pangaea.

He suggested that the continents began separating due to forces resulting primarily from the Earth's rotation (centrifugal force). Currently, the scientific community accepts the concept of continental movement, but the specific causes proposed by Wegener (centrifugal force) are rejected in favor of the mechanisms explained by plate tectonics.

Characteristics of the Ocean Floor

Modern studies of the seabed, utilizing new technologies, provide the following key information:

• a) The seabed has a varied relief, including features like mid-ocean ridges and oceanic trenches.
• b) There is an unequal distribution of sediments; they are thinner near the ridges and thicker further away.
• c) The age of the oceanic crust rocks is relatively young, generally not exceeding 180 to 200 million years (Ma).

Understanding Earth's Interior Structure

We do not know the Earth's interior exactly, as direct observation is severely limited (drilling has only reached shallow depths). The study of the Earth's interior is primarily performed using indirect methods, which provide data allowing scientists to construct structural models of the inner Earth.

Indirect Evidence and Data

The key data points derived from indirect methods include:

• a) Density: Materials inside the Earth are significantly denser than those found on the surface.
• b) Temperature: Temperature increases with depth, reaching approximately 5,500°C in the center.
• c) Magnetism: The Earth behaves like a magnet, suggesting that one of its inner layers (the outer core) must be composed of moving, conductive material (metallic).
• d) Behavior of Seismic Waves: Observing changes in the speed and direction of seismic waves at specific depths indicates that the Earth's interior is divided into distinct layers. Each abrupt change in wave behavior is known as a discontinuity.