Cosmology, Earth's Structure, and Plate Tectonics

Geocentric

The ancient view that all heavenly bodies revolve around Earth.

Heliocentric

Proposed later, this model places the Sun at the center, with Earth and other planets orbiting it.

Star

A giant, hot gas ball (mostly hydrogen and helium), held together by gravity, undergoing nuclear fusion.

Galaxy

A huge collection of stars (billions), gas, and dust bound by gravity (e.g., the Milky Way).

Universe

Everything that exists—billions of galaxies.

Big Bang

Created the lightest elements: H and He.

Stellar Fusion

In stars, H and He fuse to create heavier elements up to iron (Fe).

Supernova Explosions

When stars die in violent explosions, they form heavier elements (everything beyond iron).

Nebular Theory

Solar systems form from rotating disks of gas and dust. Gravity pulls material together to form planetesimals → planets.

Crust

Rocky and cool.

Mantle

Rocky and hot (solid but flows).

Outer Core

Liquid iron (produces magnetic field).

Inner Core

Solid iron (very hot).

Chemical Composition of Crust

O, Si, Al.

Chemical Composition of Mantle

O, Si, Mg.

Chemical Composition of Core

Mostly iron (Fe).

Wegener's Continental Drift Hypothesis

Continents fit together like puzzle pieces (e.g., South America & Africa) and have similar fossils, rocks, glacial marks.

Seafloor Spreading

New Crust forms at mid-ocean ridges and spreads outward; Old Crust gets recycled at trenches (subduction zones).

Planets in Habitable Zone

Planets that formed in the habitable zone (like Earth) could have liquid water.

Marine Magnetic Anomalies

Earth's magnetic field flips every ~few hundred thousand years. Iron in magma locks in the magnetic direction as it cools. Reversals leave symmetrical "stripes" on both sides of ridges.

Tectonic Plate

A slab of the lithosphere (crust + upper mantle) that moves as a rigid unit.

Plate Movement Rate

Plates move ~1-15 cm/year.

Driving Forces of Plate Movement

Driven by mantle convection, ridge push, slab pull, and mantle drag.

Divergent Boundary

Plates move apart, new crust forms.

Convergent Boundary

Plates collide; subduction or mountain building.

Transform Boundary

Plates slide past one another.

Mid-Ocean Ridges

Magma rises as plates pull apart → forms new ocean crust.

Pillow Lava

Underwater lava that cools into blobs.

Shallow Earthquakes

Happen as crust cracks and cools.

Subduction Zones

Oceanic crust sinks beneath another plate → trenches, volcanoes, earthquakes (e.g., Japan, Andes).

Collision Zones

Two continental plates crash → mountain ranges (e.g., Himalayas).

Deep Earthquakes

Deep and powerful earthquakes occur in subduction zones.

Transform Boundaries

Plates grind past each other horizontally.

Earthquake Causes

Cause frequent earthquakes, especially near faults (e.g., San Andreas).

Big Bend of San Andreas

Builds pressure → increased earthquake risk.

Mantle Convection

Hot mantle rises, cool mantle sinks = convection.

Plate Motion Mechanisms

Plates are dragged and pushed due to slab pull, ridge push, and mantle drag.

Volcano Formation

Volcanoes form as plates move over hot spots.

Hot Spots

Plumes of hot magma that rise from deep mantle, fixed in position. Volcanoes form as plates move over them.

Igneous Rock

Formed from cooled magma/lava.

Sedimentary Rock

Formed from compressed sediments.

Metamorphic Rock

Pre-existing rocks changed by heat/pressure.

Extrusive Igneous Rock

Lava cools on surface (fast) → small crystals (e.g., basalt, pumice).

Intrusive Igneous Rock

Magma cools underground (slow) → large crystals (e.g., granite).

Mafic Rock

Hotter, low silica, runny viscosity, typically found in shield volcanoes (e.g., Mauna Loa).

Felsic Rock

Cooler, high silica, thick viscosity, typically found in stratovolcanoes (e.g., Mt. Fuji).

A'a Lava

Jagged lava flow (cooler/faster).

Pahoehoe Lava

Smooth, ropey lava (hotter/slower).

Obsidian

Fast-cooled felsic lava = volcanic glass.

Pumice

Light, bubbly rock from gas-rich felsic eruptions.

Sedimentary Rock Formation Process

1. Weathering/Erosion → Rocks break into pieces (clasts); 2. Transport → Wind/water moves clasts; 3. Deposition → Sediments settle in basins; 4. Lithification → Compression and cementation.

Breccia

Rock formed from angular clasts, typically from glaciers.

Conglomerate

Rock formed from rounded gravel, typically from rivers.

Sandstone

Rock formed from sand, typically found in beaches/deserts.

Shale

Rock formed from mud, typically found in marshes/estuaries.

Limestone

Rock formed from shells, typically found in coral reefs.

Coal

Rock formed from organic matter, typically from swamp plants.

Metamorphic Rock Formation

Heat + Pressure + Shear changes existing rocks, happens deep underground (high temp & pressure).

Marble

Metamorphosed limestone, more durable, used in buildings.

Plinian Eruption

Named after Pliny the Younger, characterized by powerful blasts, ash/gas/rock.

Pyroclastic Flow

Hot gas + rock avalanche, super fast (100-500 km/hr).

Lahar

Volcanic mudflow, mixes ash + water.

Ash Cloud

Fine dust particles that can disrupt air traffic & cool climate.