Earth and Space Science Y8 T4

Inner core

A layer at the centre of the Earth made of solid iron and nickel because of immense pressure. Very dense, 1000km thick, 6000 dg hot.

Outer core

A layer of molten iron and nickel that surrounds the inner core of Earth. Dense, 2000km thick, 5000 dg hot.

Mantle

The layer of hot, solid material between Earth's crust and core. 3000 km thick, 2000 dg hot, solid silicate rocks rich in iron and magnesium

Crust

The thin and solid outermost layer of the Earth above the mantle. 10-50 km thick, 22 dg near the surface, made of mainly silicon & oxygen & nitrogen, least dense

Lithosphere

A layer on the Earth's surface composed of the crust and the semi-rigid part of the UM. Has varied thickness and is dense.

Asthenosphere

The semi-liquid part of the UM, a layer below the lithosphere. Is 80-200 km thick and is less dense than the lithosphere.

Geosphere

Solid parts of Earth; rocks, minerals, landforms

Continental crust

The part of the Earth's crust that primarily contains granite. is less dense than oceanic crust, is 20-50 km thick, and is very old

Oceanic crust

The part of the Earth's crust that primarily contains basalt. is denser than continental crust, is 8 km thick, and is the youngest layer.

Plate tectonics

A theory stating that the Earth's lithosphere is broken into several rigid plates that float on the asthenosphere below.

Convection currents

The flow of heat in the mantle that drives the movement of tectonic plates.

Constructive plate boundary

A boundary where tectonic plates move apart, creating new crust (e.g., mid-ocean ridges).

Destructive plate boundary

A boundary where tectonic plates converge, causing subduction or the formation of mountains.

Fault

They are breaks in the Earth's crust and occur when too much stress is applied to the rock.

Fold

Bending of rock layer when stresses are applied to both ends of a section of rock.

Compressional stress

When rocks push against each other and cause folding

Tensional stress

When rocks pull away from each other and cause stretching

Shear stress

When rocks slide past each other and cause tearing

Normal fault

A type of fault where the hanging wall slides downward; caused by tensional stress in the crust

Reverse fault

A type of fault where the hanging wall moves up; caused by compressional stress in the crust

Transform (strike-slip) fault

A type of fault where both plates slide past each other; caused by shear stress

Anticline

Upward curves (rainbow)

Syncline

Downward curves (smile)

Footwall

The block of rock that forms the lower half of a fault

Hanging wall

The block of rock that forms the upper half of a fault.

Where faults occur

Along tectonic plate boundaries

Where folds occur

Along plate boundaries, in areas under compressional stress

Why faults occur

Occur because of the movement of tectonic plates and the stress that builds up in the Earth's crust

Why folds occur

Occurs because of lots of stress over long periods of time on rocks

Explain why different layers have different compositions and consistencies

As Earth formed and heated up, heavier materials like iron and nickel sank toward the center forming the core, while lighter silicate minerals rose to form the mantle and crust. This process is called planetary differentiation and caused each layer to have a different chemical composition and separated materials based on density and chemical properties.

Theory of Plate Tectonics

Plate tectonics is the theory that the Earth's lithosphere is divided into several rigid plates that float and move slowly over the semi-liquid asthenosphere below. These plates interact at their boundaries and cause geological activity like earthquakes, volcanoes, and mountain formation.

Plate movements caused by…

Caused by convection currents in the mantle and outer core

The 7 major tectonic plates

Pacific, Antarctic, African, Eurasian, North American, South American, Indo-Australian

The role of heat energy and convection currents that drive the movement of plates

Heat energy is produced in the Earth's core when heavy elements in the core decay, producing radioactive heat. The heat energy causes the mantle's molten rock to heat up, become less dense, and rise toward the crust. As it cools near the surface, it becomes denser and sinks back down, creating convection currents. These currents act like a conveyor belt and slowly move the tectonic plates above by dragging or pushing them in different directions.

List the pieces of evidence for continental drift

Continents fit together like a puzzle, similar fossils found across continents, shape of the ocean floor and the age/polarity of ocean sediments, glaciers and glacial deposits.

Expand on the evidence point; continents fit together like a puzzle

The coastlines of continents such as South America and Africa fit together like puzzle pieces, especially when the edges of the continental shelves are matched, suggesting they were once joined.

Expand on the evidence point; similar fossils found across continents

Identical fossils of extinct plants and animals, like the freshwater reptile Mesosaurus, are found on continents now separated by oceans, implying these lands were once connected since these species could not have crossed vast oceans.

Expand on the evidence point; shape of the ocean floor and the age/polarity of ocean sediments

Long mid-ocean ridges where new crust forms was found on the ocean floor. When this crust cools, iron minerals inside align with Earth's magnetic field, which has flipped directions many times over history. This creates symmetrical stripes of normal and reversed magnetic polarity on each side of the ridges. The youngest rocks are at the ridge, and rocks get older moving away, showing new crust is continuously added and the seafloor spreads. Shows that ocean floors grow and support continental drift.

Expand on the evidence point; glaciers and glacial deposits

Glacial deposits are found on continents near the equator today, such as South America, Africa, India, and Australia, indicating these continents were once located near the poles where glaciers could form, consistent with continental movement.

Divergent boundary definition

The boundary between two tectonic plates that are moving away from each other

Convergent boundary definition

Boundary between two plates that are colliding

Transform boundary definition

Boundary between two plates that are sliding past each other

What happens with a O-C collision?

Dense oceanic plate collides with less dense continental plate. The subduction zone is where the denser plate slides under the less dense plate

What happens with a O-O trench collision?

The denser plate slides under the less dense plate creating a deep trench where they first meet

What happens with a O-C trench collision?

As the oceanic plate subducts, it 'pulls on' the edge of the continental plate and pulls it down to form a crease. Causes a deep trench off the edge of land

What happens with a C-C collision?

Neither plate 'wants' to subduct so either: both push upwards or one subducts but also pushes the upper plate upwards.

What can divergent boundaries result in?

Sea-floor spreading, mid-ocean ridges, fissure volcanoes, rift valleys

Sea-floor spreading

1. Happens when two oceanic crusts collide (O-O)

2. As the plates move apart, new magma/lava flow up slowly to fill the fault or gap and creates new oceanic crust. This results in a 'flat' sea floor.

3. Is a process at mid-ocean ridges

Mid-ocean ridge

1. Happens when two oceanic crusts collide (O-O)

2. These occur during seafloor spreading when the magma/lava flows out faster than the plates are moving apart. The lava cools quickly and creates a mini mountain chain or ridge under the water. As the plates move apart, the ridge 'cracks' and more lava fills the gap.

3. Mid-Atlantic Ridge, Red Sea Ridge

Fissure volcanoes

1. C-C

2. Similar to seafloor spreading but occurs on land. Magma flows out slowly (no eruption) to fill the gap and sometimes builds a ridge once it cools.

3. Laki (Iceland), Deccan Traps

Rift valleys

1. C-C

2. Similar to seafloor spreading, but no magma/lava flows out so a gap or valley is formed

Rio Grande Rift, Baikal Rift Valley

What can convergent boundaries result in?

Volcanic mountains, island arcs, trenches, thrust mountains

Volcanic mountains

1. O-C

2. The heat from the friction between the plates partially melts the crust. Newly formed magma rises and forms volcanoes. Over time, volcanic mountain chains are formed.

3. Andes, Sierra Nevada's

Island arcs

1. O-O trench

2. Heat from friction between plates causes the subducting plate to melt. Magma rises to the surface and forms volcanoes under the ocean. When these penetrate the ocean surface, they form island arcs

3. Japan, New Zealand

Trenches

1. O-C trench

2. As the oceanic plate subducts, it 'pulls on' the edge of the continental plate and pulls it down to form a crease. Causes a deep trench off the edge of the land

3. The Mariana Trench

Thrust mountains

1. C-C

2. The collision pushes up the crust to form thrust mountains.

3. Himalayas, European Alps

What can transform boundaries result in?

A fault line, earthquakes

Fault line

1. The meeting point between the two plates is called a fault. If the plates move very slowly and without too much friction, a gap or fault line will develop.

2. California fault line, Turkey fault line, San Andreas fault

Earthquake

1. Pressure can build at the fault line as the two plates 'try' to move but are prevented by friction. Eventually, friction no longer can stop them moving and they slide past each other very quickly, creating earthquakes.

2. Haiti earthquake, Valdivia earthquake

Rock

A naturally occurring solid composed of one or more minerals.

Igneous rock

Rocks that have formed when molten magma or lava that has cooled and solidified.

Intrusive (plutonic) rock

Rock formed when magma cools slowly below the surface, which forms larger crystals

Extrusive (volcanic) rock

Rock formed when magma cools quickly above the surface, which forms smaller crystals

Igneous rock characteristics

o Usually have a crystalline (interlocking) texture (large for intrusive, small for extrusive)

o Hard and dense

o No fossils

o Can be glassy, coarse, or fine-grained

o Wide color range

o Often lack layers

o Pores/holes (in extrusive rock)

Examples of igneous rock

Basalt, obsidian, granite

Metamorphic rock

A rock type formed when existing rocks (igneous and sedimentary) undergo intense heat and pressure, causing them to recrystallise forming a new texture and mineral composition.

Metamorphic rock characteristics

o May have banding or foliation

o Crystalline texture

o Sometimes show distorted fossils

o Rarely have pores or vesicles

Metamorphic rock examples

Slate (from shale), marble (from limestone), gneiss (from granite), quartzite (from sandstone)

Sedimentary rock

Rocks formed from layers of sediments such as sand, silt and dead plants compacted and cemented over time

Sedimentary rock formation

Formed when weathering/erosion occurs to other rocks, small particles are carried away from the original rock and into water bodies where they settle to the bottom (sediment) and the pressure compacts and the dissolved chemicals in the water crystalise - solidifying into rock.

Sedimentary rock characteristics

o Has layers (strata)

o May include fossils

o Softer and less dense than igneous or metamorphic