Chapter 1 - Plate Tectonics

Vocabulary flashcards covering the Earth's age, inner core, outer core, magnetic field, and internal layer structure.

Earth's Formation and Age

The Earth is approximately $4.54\,\text{billion years}$ old; its early surface was between $2000^\circ\text{C}$ and $3000^\circ\text{C}$ and mainly molten. The Earth cooled slowly as heavy materials like nickel and iron sank to its centre.

Earth's Internal Structure

The cross-sectional layer structure of the Earth consisting of the oceanic crust, continental crust, Moho line, solid upper mantle, lithosphere, asthenosphere, lower mantle, outer core, and inner core.

Inner Core

The layer at the very centre of the Earth that is $1220\,\text{km}$ thick with temperatures of $5000^\circ\text{C} - 6000^\circ\text{C}$; it remains solid due to intense pressure and is made up of $90\%$ iron with small amounts of nickel and sulfur.

Outer Core

A $2200\,\text{km}$ thick molten layer composed of iron and nickel with a temperature of roughly $4000^\circ\text{C}$, which is liquid because pressure is lower than in the inner core. It generates the magnetic field.

Magnetic Field

A protective invisible force generated by the movement of the outer core around the inner core which shields the Earth from harmful radiation.

Mantle

The mantle is 2900km thick, makes up 75% of the Earth’s volume and its divided into three sections

The lower mantle

Composed of solid rock, the heat from the mantle causes columns of molten magma to form, to rise away and cool and eventually sink down. This creates convection currents, they are responsible for endogenic forces, from deep within the Earth that causes movements on the crust.

Asthenosphere

The layer of the Earth's upper mantle situated directly below the solid upper mantle (lithosphere). is a 100km -200km thick zone, is made up of semi-molten magma, due to intense pressure and heat. Creates plasticity - slow flowing movement of semi-molten magma.

Lithosphere

The rigid structural region of the Earth composed of the crust and the solid upper mantle. 50km to 200km. It is solid and rigid, the lithosphere is brittle and is broken into plates.

The Crust

The outer layer of the Earth, made up of solid rock. Two types of crust.

The continental crust

makes up the continents of the world, 45km average. The rocks are light eg granite - made up silica and aluminium known collectively as sial. crust is thin as 30km and thick as 70km.

The oceanic crust

is made up of oceans and seas, thinner than continental crust, 8km thick. Rocks are dense and heavy eg basalt made up silica and magnesium, known collectively as sima.

Discontinuities

refers to boundaries where one layer of the Earth ends and another layer begins. There are two discontinuities Gutenberg and Mohorovicic (Moho) discontinuity

The Gutenberg discontinuity

located roughly 2900km below the Earth’s surface, where the outer core meets the lower mantle

The Mohorovicic discontinuity

located 30-50km below continental crust, referred to as Moho and marks the boundary between the solid upper mantle and the crust

The theory of plate tectonics

The theory of plate tectonics explains how this movement occurs and the effect it has on the Earth’s surface

Processes that cause plate movement

Thermal convection currents, Ridge push, Subduction and slab pull

Thermal convection currents

in 1928 British geologist Arthur Holmes suggested Thermal convection current as as a way in which the Earth’s huge tectonic plates can move, it is created in the lower mantle as the intense heat from the core forms magma. As the magma reaches the upper mantle it cools and becomes semi-molten. The cooling magma moves laterally beneath the lithosphere. this movement causes friction which causes the plates to move apart, collide or slide past each other.

Ridge push

Is a process that explains how plates separate at mid- ocean ridges. magma rises upwards between separating plates before pouring out on to the ocean floor as lava and cooling to form solid rock called basalt.The newly formed rock is light so it sits on top of the older rock. as the new rocks begin to cool they contract and become dense causing it to slide downward this pushes the rest of the plate away.

Subduction and slab pull

Destroying of seafloor, Fredrick Vine and Drummond Matthews studied ocean floor and led to the discovery of deep ocean trenches formed by subduction.

Subduction

A process in which heavy oceanic crust bends downwards into the mantle and melts at a depth of roughly 100 km100km. A deep oceanic trench forms where one plate subducts beneath the overlying plate, influencing the speed of plate movement

Slab Pull

Occurs when a heavier oceanic plate sinks into the less dense asthenosphere, dragging the rest of the plate after it, causing subducting plates to move faster than other plates.

Continental drift

The theory first proposed by Alfred Wegener in 1912 stating that all of Earth's landmasses were once joined together in a single supercontinent called Pangea, which began breaking apart roughly 200 million years200million years ago into Laurasia and Gondwanaland.

Continental fit

Proof of continental drift showing that continental shelves fit together like a jigsaw puzzle, such as the matching coastlines of the east coast of South America and the west coast of Africa.

Matching plant fossils

Fossils of the Glossopteris plant found across South America, Africa, India, Australia, and Antarctica, which supports continental drift because the plant grew under specific climate conditions across currently separated continents.

Matching animal fossils

Fossils of the ancient freshwater reptile Mesosaurus found in both South America and Africa, proving the continents were once connected because it could not swim across saltwater oceans like the Atlantic.

Matching rock folds

Identical rock folds are found along the eastern coast of North America Appalanchian mountains ans the north western of Europe Ireland and Scotland. These mountains were formed 400 million years aho and are made of the same rock, granite, Wegener suggested that they were once a single mountain range.

Seafloor spreading

Seafloor spreading is the widening of the ocean where convection currents cause a gap to develop between tectonic plates

Proof 1 of seafloor spreading - Age of seafloor

Rocks closest to a ridge is much younger than rock closes to a continent. Seafloor nearest Mid Atlantic Ridge is 10 million years old and Seafloor near North America and Europe is 180 million years old

Proof 2 of seafloor spreading - Ocean sediment

Seafloors are gradually covered in sediment over time. Seafloor close to continents has much thicker layers of sediment than seafloor close to mid-ocean ridges