science earth and space yr 9 revision

what are the layers of the earth

crust, mantle, outer core, inner core

describe the crust

• thinnest layer

• avg thckness is 35 km

• crust thicker on land than water

describe the mantle

• contains higher amounts of iron, calcium and magnesium

• 2900km thick dense rock

• areas flow like thick fluid

• upper=plastic like

• lower=rigid

describe the core of the earth

• temp: 5200 degrees celcius

• inner core solid because intense pressure of layers

• made of iron and nickel

what are the main tectonic plates

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

what is continental drift

the gradual movement of the continents across the earth's surface through geological time

what are continental shelves

gently sloping edge of a continent that extends from the shoreline to the continental slope

what is seafloor spreading (hess’s threory)

new oceanic crust formed at mid-ocean ridges during spreading

tectonic plate theory

the lithosphere of the earth (the crust and top of the mantle) is broken up into large pieces called tectonic plates that move over semi-molten asthenosphere (plasticy top part of mantle)

evidence supporting the theory of plate tectonics

• how continents fit like puzzle pieces

• identical fossils and rocks on different continents

• distribution of volcanoes and earthquakes on boundaries

• magnetic striping

• similar geological sturctures

process of seafloor spreading

magma pushes up between two plates and then oozes out to solidify, which then creates a divergent boundary. the plates start to push apart due to the constant pressure from the magma, and sediments and rock aslo start to come along with them. the fault is where most of the newer rock is

how do plates move from convection currents in the earth’s mantle

when plates are dragged along the asthenosphere, and the magma rises up and then flows under plates, creating convection currents

explain this image

the magma rises from the fault line and over time it moves to continental crust and subduct as it is being pushed apart towards the next continental crust. it then melts back to magma and resurfaces.

diverging boundary and give example

tectonic plates are moving apart from each other

eg,

• mid atalantic ridge is when north american and Eurasian plates split apart (oceanic)

• east african rift between nubian and somali plate

converging boundary and examples

plates collide with each other

continental 2x: Himalayas- eurasian and Indian plates

oceanic continental: andes mountains- nazca subducts under north American plate

ocenanic 2x: maraina trench subducts pacific and phillipine sea plate

transform boundaries and example

plates that slip past each other

• Alpine fault between pacific and Australian plate

subduction

an oceanic plate sinking under a lighter continental plate and become distorted forming fold mountains and volcanoes

fault

a fracture or zone of fractures in the Earth's crust where rocks have moved past each other, causing a displacement

rift valley

an area where the earth’s crust is splitting apart

mid ocean ridge

a continuous undersea mountain range formed at a divergent tectonic plate boundary where new oceanic crust is create

what do each of the boundaries create

• Divergent: mid-ocean ridges and rift valleys

• Convergent: mountain ranges, volcanoes, and trenches

• Transform: earthquakes and feature valleys/block mountains

causes of earthquakes

sudden release of energy form the movement of tectonic plates along faults of boundaires

methods of detecting earthquakes

seismometer detect earthquakes. the machine uses inertia to stabilise the pen and the rest of the machine moves with the vibrations of the Earth

p-waves(primary waves)

• longitduinal waves (back and forth)

• fastest wave

• weakest wave

s-wave (secondary wave)

• transverse waves (up and down)

• slower than p-waves

• stronger than p-waves

surface waves

• slowest 

• most destructive

• travel along the earth;s surface

focus

place where the quake starts

• 100’s km deep in the  Earth

epicentre

surface directly above the focus 

• buildings near it would be damaged

oceanic crust

• found on ocean floor

• thinner

• denser (iron+magnesium)

continental crust:

• crust forming continents rising above sea level

• thicker

• lighter (aluminium+silicon)

where and how volcanoes form: divergent, convergent

divergent plate: magma rises to fill fault line, cools + hardens, creating new crust. slowly builds up into mountain that has a way to spew magma

convergent: sub ducting, oceanic plate melts from high pressure and makes less dense magma, which then resurface as an eruption from a volcano

where and how are earthquakes formed: convergent and diverent

convergent:

• most and strongest earthquakes are from convergent boundaries

• when the plates collide, the stress builds up and it releases seismic waves through the ground, causing an earthquake

divergent:

• plates move out causing sudden slips in between tectonic plates

destructive landforms with divergent boundaries

• mid-ocean ridges: plates in ocean pull apart then magma fills the gap making underwater mountain ranges

• rift-valleys: the stretched crust creates a valley

• Volcanic islands: magma constantly spewing out to create a volcano that has a bigger base that it creates an island

destructive landforms woth convergent boundareis

• fold mountains:plates push upwards to make mountain slowly

• trenches: subducted plates creates depressions on the sea floor

• volcanic arcs: product of oceanic floors subducting pushing magma up to create a chain of volcanoes parallel to each other