Earth Science Lecture Notes Review

Early Theories:
- Capture Hypothesis: Earth captured a small planet, which became the Moon.
- Accretion Hypothesis: Earth and Moon formed together from the same accretion disc.
- Collision (Giant Impact) Hypothesis: Current understanding is that a Mars-sized protoplanet (Theia) struck the Earth, creating a molten Earth and a debris field that coalesced to form the Moon.

Core Idea: The Moon formed from a collision between the Earth and another small planet, about the size of Mars.
Debris collected in orbit around Earth to form the Moon.
The colliding body is sometimes called Theia, named after the mythical Greek Titan, the mother of Selene (goddess of the Moon).
Analysis of lunar rocks (2016) suggests a direct hit, causing thorough mixing of both parent bodies.

The surface of the Earth doesn't appear to have ever been molten, while the collision would have caused the surface to melt.
Venus has no moon, despite collisions being common in the early Solar System (scientists would expect Venus to have formed a moon the same way).
The composition of rocks on the Moon would be more similar to Theia than rocks on Earth.

A nebula is a giant cloud of dust and gas, primarily hydrogen and helium, in space.
Nebulae originate from gas and dust thrown out by the explosion of a dying star, such as a supernova.
Other nebulae are regions where new stars are beginning to form and are called "star nurseries."

An area of outer space within a dense nebula where gas and dust are contracting, resulting in the formation of new stars.

Stars form when clumps of hydrogen and other gases collapse under their own gravity.
As the collapse continues, the central clump grows stronger, and the gas heats up due to the conversion of gravitational potential energy into thermal energy.
When the temperature gets high enough, nuclear fusion ignites, forming a protostar.
The protostar emits enough energy to counterbalance its own gravitational pressure, and a cloud of material remains around the newly born star.
This cloud remnant is the protoplanetary disk, where planets may form around the star.

Stars are born from nebulae.
As the nebula gains mass, its gravitational forces build.
The inner part of the cloud heats up, becoming a protostar.
When the core heats up enough to cause nuclear fusion of hydrogen into helium, a star is born.

The continental drift hypothesis, proposed by Alfred Wegener, stated that the continents were assembled to form the supercontinent Pangaea and moved through time.

Fit of the continents.
Fossil evidence (similar fossils on different continents).
Ancient mountain ranges.
Past climate evidence (e.g., glaciers at the South Pole, swamps in tropical regions).

Convection currents drive the movement of Earth's rigid tectonic plates in the planet's fluid molten mantle.
Where convection currents rise up towards the crust's surface, tectonic plates move away from each other in seafloor spreading.

Oceanic Plates:
- Consist of oceanic crust called "sima" (silicon and magnesium).
- Formed by divergent plate boundaries.
Continental Plates:
- Consist of continental crust called "sial" (silicon and aluminum).
- Formed primarily by convergent plate boundaries.

A volcano is a feature in Earth’s crust where molten rock is squeezed out onto the Earth’s surface.
Molten rock is called magma beneath the surface and lava when it erupts from a volcano.
Volcanoes release lava, gases, ash, and solid rock.

Earth's magnetic poles have swapped approximately 200 times in the last 100 million years.