Science

Year 8 - earth

Inner core

A dense sphere of solid iron and nickel at the center of Earth.1200 kilometres

Outer core

the liquid layer of the Earth's core that lies beneath the mantle and surrounds the inner core. 2260km. Made of liquid iron and nickel

Mantle

The layer of hot, solid material between Earth's crust and core. 2900km. Made of silicate rock

Crust

the earth's outer layer made of solid rock. 5-70km.

Lithosphere

The brittle, solid crust and uppermost solid mantle, broken into tectonic plates

Oceanic Crust

A part Earth's crust that is usually below the oceans and not associated with continental areas, thinner and higher in density - 5-10km- mainly granite

Continental Crust

the relatively thick part of the earth's crust that forms the large landmasses. It is generally older and more complex than the oceanic crust. 30 - 50km. mainly Basalt

Alfred Wegener

all landmasses formed one supercontinent called Pangaea (meaning 'all lands'), before gradually rifting apart and drifting across the globe. continents are not stationary fixtures. Was initially rejected because there was no evidence. Later mantle convection and seafloor spreading was discovered

Wegener’s evidence

Jigsaw fit - Coastlines of south america and africa

Seafloor spreading

New crust forming at ocean ridges and spreading outwards

Why Density Matters: Subduction

More dense = sinks, less dense = floats. The oceanic plate sinks beneath the continental plate in a process called subduction.

Seafloor conveyer belt

Magma rises at mid-ocean ridges, creating new crust and pushing older seabed away on both sides.

Evidence for seafloor spreading - Harry Hess

1. Age of Seafloor Rocks - older rocks are further away

2. Magnetic Reversals - symmetrical bands record earth’s magnetic reversals overtime

3. Sediment Thickness - thinnest near the ridge and thickest near continent

Paleomagnetism

is the study of ancient magnetism locked in cooling rock.

Mantle convection

Hot rises, cool sinks. This slow movement in the mantle acts like a conveyor belt that pushes and pulls tectonic plates.

Three types of plate motion

Convection Currents

Ridge Push

Slab Pull

Divergent boundaries

The plate boundary is when plates pull apart, creating new crust. Creates volcanoes

Convergent boundaries

The plate boundary is when plates collide, destroying or crumpling. Creates volcanoes

Transform boundaries

This plate boundary is when plates slide horizontally past one another. Creates earthquakes

Asthenosphere

Semi-fluid, ductile upper mantle layer where high heat and pressure allow slow plastic flow

The driving forces of plate motion

Step 1 Mantle convection

Step 2 Ridge push

Step 3 Slab pull

Epicentre

Point on the surface above the focus; typically where it is most shaky.

Focus point - earthquakes

the underground point where rock first breaks and seismic energy is released

Fault plane - earthquakes

fracture zone where rock masses slip past eachother