test 2 lectures 12-13

Dynamic Planet

Earth Systems

• Endogenic Processes: These are internal processes that generate heat and material from deep within the Earth's crust. They involve phenomena like tectonics, earthquakes, and volcanism. The main energy source for these processes is radioactive decay.

• Exogenic Processes: These are external processes that are powered by the energy from the sun. They include weathering (breaking down rocks), erosion (wearing away of the land), river systems (how rivers shape the landscape), ocean action (effects of oceans on land), and glacial activity (movement of glaciers).

Geologic Time Scale

• This scale represents the history of Earth, divided into Eons, Eras, Periods, and Epochs.

• Major Eons include:

  • Precambrian (spans 88.3% of Earth's history)

  • Paleozoic (4.0%)

  • Mesozoic (1.5%)

  • Cenozoic (6.3%)

Key Events:

• The first appearance of hominids (early human ancestors) happened in the Holocene Epoch, about 11,500 years ago.

• Major extinctions occurred in history, such as the extinction event that led to the downfall of dinosaurs, paving the way for the major development of flowering plants.

Superposition Principle

• Superposition states that in layers of sedimentary rocks, the younger layers (beds) are on top of the older ones if they haven't been disturbed by external forces.

Age of Earth

• The Earth is estimated to be roughly 4.6 billion years old. The oldest known rocks are about 4.0 billion years old, and the oldest fossils date back approximately 3.5 billion years.

• Radiometric Dating helps measure the age of rocks by calculating the decay rates of certain isotopes (which have a known half-life).

Earth's Structure

• Composition and Density:

  • Crust:

    • Oceanic crust: Density of 3.0 g/cm³ (average thickness: 5 km).

    • Continental crust: Density of 2.7 g/cm³ (average thickness: 30 km).

  • Core: Composed of an inner solid core and an outer liquid core, mainly made of metallic iron. The core represents about one-third of Earth's mass and one and a half times its volume.

Layers of Earth

• Lithosphere: This is the rigid outer layer that includes the crust and the uppermost part of the mantle.

• Asthenosphere: Located beneath the lithosphere, this layer is softer and can flow when under stress.

• Mohorovičić Discontinuity: This is the boundary that separates the crust from the uppermost mantle.

Buoyancy and Isostasy

• Buoyancy: The Earth's crust floats on denser layers beneath it, similar to how wood floats on water.

• Isostatic Rebound: When a heavy object (like a glacier) is removed, the crust will rise to compensate for the loss in weight.

Processes of Isostasy and Terrain Adjustment

• Terrain (landforms) adjusts through processes like uplift (where land rises) or subsidence (where land sinks) due to weight and erosion.

• Example: Mountains may adjust due to weathering and the movement of sediments.

Rock Cycle

• The rock cycle describes how rocks are formed, broken down, and reformed.

• Igneous Rocks: Formed by the cooling of molten rock (magma).

• Sedimentary Rocks: Made from compacted sediments; they can be classified as clastic, chemical, or biological.

• Metamorphic Rocks: Created from existing rocks that are altered by heat, pressure, or chemical processes.

Common Elements in Earth's Crust

• The main elements by weight in Earth's crust are:

  • Oxygen (46.6%)

  • Silicon (27.7%)

  • Aluminum (8.1%)

  • Iron (5.0%)

  • Calcium (3.6%)

  • Sodium (2.8%)

  • Potassium (2.6%)

  • Magnesium (2.1%)

Plate Tectonics

• Types of Plate Boundaries:

  • Convergent Boundary: Where plates collide, creating zones of subduction (one plate going under another), causing mountains and volcanism.

  • Divergent Boundary: Where plates move apart, leading to the creation of new oceanic material at mid-ocean ridges.

  • Transform Boundary: Where plates slide past each other, often causing earthquakes.

Crustal Formation Processes

• These processes are driven by tectonic movements, resulting in various geological formations.

• Magma Generation: This occurs from the melting of subducted plates and the material in the asthenosphere.

Stress and Strain in Rocks

• Rocks respond to stress (force applied) through strain (deformation), which can lead to:

  • Tensional Stress: Results in stretching and thinning (causing normal faults).

  • Compressional Stress: Causes shortening and folding (leading to reverse faults).

  • Shear Stress: Causes lateral twisting (resulting in strike-slip faults).

Conclusion

• Understanding these geological processes is essential for grasping how dynamic and ever-changing Earth's landscapes are.

Formation of Earth

• The Earth formed around 4.6 billion years ago from a solar nebula, which is a massive rotating cloud of gas and dust surrounding the young Sun. This process led to the accumulation of particles that gradually stuck together under the force of gravity, forming planetesimals and eventually larger bodies, including Earth.

• In its early history, the Earth was molten due to intense heat caused by gravitational compression, radioactive decay, and numerous collisions with other bodies. As the planet cooled, the outer layers solidified forming a crust, while the interior remained hot and partially molten, which led to tectonic