Earth's Layers and Plate Tectonics

• The learning objectives are to explain continental drift and plate tectonics, construct a model of tectonic plate movement, and demonstrate an appreciation for Earth's dynamic nature.

Earth's Layers

• The Earth consists of the crust, mantle, and core.

Crust

• The outermost layer of the Earth.
• It is the thinnest layer with a thickness ranging from about 5 to 70 kilometers
• It is divided into the continental crust and the oceanic crust.

Continental crust

• The thicker layer of the Earth's crust.
• It is found under the continents.
• It averages about 35 kilometers thick.

Oceanic crust

• The thinner layer of the Earth's crust.
• It is found under the ocean basins.
• It is about 7 kilometers thick on average.

Mantle

• The layer beneath the Earth's crust.
• The thickest layer can be found at a depth of approximately 2,900 kilometers.
• The mantle is divided into an upper and lower layer.

Upper mantle

• The upper mantle is relatively rigid and contains the asthenosphere, a semi-fluid layer that allows the movement of tectonic plates.

Lower mantle

• The solid lower mantle contributes to the overall convection and heat transfer within the Earth's interior.

Core

• The innermost layer of the Earth, situated beneath the mantle.
• It is divided into two distinct regions: the outer core and the inner core.

Outer Core

• The outer core is a liquid layer composed mainly of molten iron and nickel.
• 2,300 kilometers thick.

Inner Core

• The inner core is the solid, central part of the Earth.
• It has a radius of about 1,220 kilometers.
• The inner core is composed of solid iron and nickel.

Plate Tectonic Theory

• The Earth's lithosphere (the rigid outer layer) is broken into large, rigid pieces called tectonic plates.
• These plates float and move on the semi-fluid asthenosphere, a hot and slowly flowing layer of the mantle beneath them.

Divergent Boundaries

• Plates move away from each other.
• This movement results in the creation of new crust as magma rises from the mantle, solidifies, and forms new oceanic crust.
• Divergent boundaries are responsible for the continuous reshaping and formation of Earth's crust.
• On land, divergent plate boundaries create mid-ocean ridges and rift valleys.
• The crust stretches and thins, magma from the mantle rises, leading to volcanic activity.

Examples

• The Mid-Atlantic Ridge and the East African Rift Valley are examples of divergent boundaries.

Convergent Boundaries

• Tectonic plates collide or come together.
• Interactions can result in geological phenomena and contribute to the formation of mountains, volcanic activity, and earthquakes.
• When two continental plates collide, neither plate is subducted due to their low density
• The plates compress and crumple, creating highly folded and uplifted mountain ranges.

Examples

• The Himalayas were formed by the collision of the Indian and Eurasian plates.
• The Mariana Trench and Andes Mountains.

Transform Boundaries

• Two plates slide past each other horizontally
• Movement along these boundaries can cause earthquakes, as the plates grind against each other.
• Transform boundaries redistribute stress and accommodate the movement between neighboring plates and do not create or destroy crust.

Example

• The San Andreas Fault in California causes earthquakes.

Pangaea Theory

• Proposed by Alfred Wegener in 1912.
• Also known as Continental Drift Theory.
• All the continents were once joined together in a single massive landmass called Pangaea, which is Greek for "all Earth", around 300 million years ago.
• Over time, Pangaea gradually broke apart, and the continents drifted to their present positions.

Evidence Supporting the Pangaea Theory

Continental Fit

• The coastlines of continents, such as South America and Africa, fit together like puzzle pieces, suggesting they were once connected.

Fossil Evidence

• Identical fossils of ancient plants and animals, such as the Mesosaurus (a freshwater reptile) and Glossopteris (a prehistoric plant), have been found on continents that are separated by vast oceans, indicating these landmasses were once connected.

Rock and Mountain Similarities

• Similar rock formations and mountain ranges are found on continents that are now far apart.
• The Appalachian Mountains in North America have similar geological features to mountain ranges in Scotland and Greenland.

Climate Evidence

• Fossilized remains of tropical plants have been found in Antarctica, suggesting that the continent was once located in a much warmer region.
• Fossilized Ginkgo leaves have been found in rock formations from the Jurassic period in Antarctica.

Breakup of Pangaea

• Around 200 million years ago, Pangaea began to break apart due to the movement of tectonic plates, forming Laurasia (North America, Europe, and Asia) and Gondwana (South America, Africa, Antarctica, Australia, and India).

Explore Earth's structure from crust to core, including the mantle and its asthenosphere. Learn about tectonic plates, their boundaries (divergent, convergent, transform), and associated geological features and events. Discover how these plates shape our planet's surface.