Structure of the Earth + Continental Drift & Plate tectonics
* school geography1. Preface
Hi, its been a while since I uploaded. Like I said before, please read my notes on https://garden.tweetor.org. it is a big inconvenience to post these.
2. Physical Geography Introduction
Physical geography deals with the natural environment. It focuses on the structure of the world around us along with the rocesses that led to the creation of the natural world
3. Three Layers of Earth
- Crust
- Cold, thin, and brittle
- Mantle
- Most of earths interior. Made of hot molten rock.
- Core
- Includes the inner and outer core. It is dense and metallic.
Each layer has a unique composition.
3.1. Earth's crust.
Surface of the earth. There are two types:
3.1.1. Continental Crust
Thick, formed of various types of rock. It is lighter and less dense. More buoyant than the Oceanic crust.
3.1.2. Oceanic Crust
It is formed of minerals: magnesum and silicate. it sinks under continental crust. The minerals come from prolonged exposure to water.
3.2. Earth's Mantle
This is the largest layer. It makes up around 85% of eaths volume. It is very hot with a 1000-3700 C, It has never been directly explored, but we can study the mantle by examining rock formations that are moved to the surface. The molten rock inside the mantle is always in motion
3.2.1. Question: Why is the mantle hot?
3.3. The Core
Extremely dense and hot: 5000-6000 C.
3.3.1. Outer Core
2,200 KM thick. Made of liquid iron and nickel.
3.3.2. Inner Core
Mostly solid due to intense [heat?] and pressure that prevents the iron and nickel from melting?.
4. Drifting Continents
4.1. Pangea
Pangea was a massive supercontinent.
Pangaea was C-shaped, with the bulk of its mass stretching between Earth's northern and southern polar regions and surrounded by the superocean Panthalassa and the Paleo-Tethys and subsequent Tethys Oceans. Pangaea is the most recent supercontinent to have existed and was the first to be reconstructed by geologists.
The geography of the continents bordering the Atlantic Ocean was the first evidence suggesting the existence of Pangaea. (“Pangaea” 2025).
4.2. Continental Drift Theory
The Continental Drift theory suggests that Earth's continents move or drift relative to each other over geologic time. This idea was first proposed by Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegener in "The Origin of Continents and Oceans." (“Continental Drift” 2026)
4.2.1. Alfred Wegener
Alfred Wegener proposed that the continents had once formed a single landmass(Pangea) before breaking apart and drifting. He was the first person to use the term "continental drift". Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift.
His hypothesis was rejected. One problem was that a plausible driving force was missing. A second was that Wegener's estimate of the speed of continental motion, 250 cm/year (100 in/year), was implausibly high. (“Continental Drift” 2026)
5. Plates
5.1. John Tuzo-Wilson
John Tuzo-Wilson was a canadian geophysicist and geologist who was known for his contributions to the theory of plate tectonics. He came up with a concept of hot spots, hot region beneath the crust. The Wilson cycle of seabed expansion and contraction is named after him. (“John Tuzo Wilson” 2026)
5.2. Plate Tectonics
Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model develops on the concept of continental drift(see: Continental Drift Theory) . Earth's lithosphere, the rigid outer shell of the planet including the crust and upper mantle, is fractured into seven or eight major plates . Where the plates meet, their relative motion determines the type of plate boundary (or fault): convergent, divergent, or transform. Faults tend to be geologically active, with earthquakes, volcanic activity, mountain-building, and oceanic trench formation.(“Plate Tectonics” 2026)
5.2.1. Plate Boundaries
Three types of plate boundaries exist,[19] characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are:
- Divergent Boundaries
When two plates slide apart from eachother. At zones of ocean-ocean rifting, divergent boundaris form by seafloor spreading, allowing for the formation of a new ocean basinc(eg: The mid-atlantic ridge). As the ocean plate splits, the ridge forms at the spreading center, the ocean basin expands, and finally, the plate area increases causing many small volcanoes and/or shallow earthquakes. At zones of continent-to-continent rifting, divergent boundaries may cause new ocean basin to form as the continent splits and ocean fills the basin. (“Plate Tectonics” 2026)
- Convergent Boundaries
When two plates slide towards eachother to form either a subduction zon(one going under another) or a continental collision.
Subduction zones are of two types: ocean-to-continent subduction, where the dense oceanic lithosphere plunges beneath the less dense continent, or ocean-to-ocean subduction where older, cooler, denser oceanic crust slips beneath less dense oceanic crust. Zones like the mariana trench are associated with ocean-ocean subduction.
In continental collision, mountain ranges often form. The plates are compressed, folded, and lifted. (“Plate Tectonics” 2026)
- Transform Boundaries
Transform boundaries occur where plates are neither created nor destroyed. Instead, two plates slide, or perhaps more accurately grind past each other, along transform faults. Transform faults occur across a spreading center. Strong earthquakes can occur along a fault. (“Plate Tectonics” 2026)
6. The mid-atlantic ridge
The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean. The ridge separates the North American from the Eurasian plate and the African plate, north and south of the Azores triple junction. In the South Atlantic, it separates the African and South American plates. The Mid-Atlantic Ridge includes a deep rift valley that runs along the axis of the ridge for nearly its entire length. (“Mid-Atlantic Ridge” 2025)
7. Sea Floor Spreading
Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. The motivating force for seafloor spreading ridges is tectonic plate slab pull1 at subduction zones, rather than magma pressure, although there is typically significant magma activity at spreading ridges.
8. Convection Currents
Warm rises Cool sinks
Convection currents are heat-driven cycles that occur in the air, ocean, and mantle. They are caused by a difference in temperature, often due to a differing proximity to a heat source. The difference in temperature relates directly to the density of the material, causing this effect.
Heat source heats fluid -> fluid expands/becomes less dense -> hot fluid rises -> fluid cools/becomes more dense -> cooler fluid sinks.
Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. (“Convection” 2026)
9. Fault Lines
Fault lines are fractures or zones of weakness in the Earth's crust where two blocks of rock move relative to each other. They are caused by tectonic forces and are where most earthquakes occur as stress is released.
10. Elsewhere
10.1. References
10.2. In my garden
Footnotes:
Slab pull is a geophysical mechanism whereby the cooling and subsequent densifying of a subducting tectonic plate produces a downward force along the rest of the plate.