Interior of the Earth

Using seismic waves to look at the Earth's interior

If Earth were made of a uniform material, P and S waves would travel through the earth on straight lines.. Studies of seismology show that this is not the case - they travel along curved paths This bending is called refraction. This indicates that rock is becomes denser with increasing depth.

Complications occur too when waves encounter the surface between two different materials Reflection and well as refraction occurs

Also P waves can be transmitted through a solid or a liquid. S waves through a solid but not a liquid.

Path of seismic waves in the Earth

S- wave shadow zone - proof that the core is liquid.

Compostion and structure of the Earths interior

Composition - clues from space

Earth has differentiated, so materials at depth different to those in crust. Meteorites give clue as to overall composition of the Earth, as these are materials from which it originally formed.

Stony Iron Chondritic

Seismic evidence

Seismic waves can be used to determine physical properties and composition of the Earth's interior, because velocities match with those determined in the lab for various materials.

Crust/Mantle

Mohorovicic discontinuity

roots under mountain belts

Mantle,lithosphere & aesthenosphere

This is what most of the Earth is made of.

Low velocity zone

Upper Mantle/Lower mantle [600km.]

Olivine --> pervoskite

Seismic tomography

Using computer imaging technology of a CAT (computerized axial tomography)

The Earth's Core

3000 km from surface. one third of mass

Complete blockage of S waves indicates that outer part is liquid

Inner core is solid

Composition - no direct observation. Compostion implied from density, mass, speed of P waves - only fit is iron. Also comparison with meteorites

Also magnetic field

Isostasy and the mantle

Phenomenon of isostasy shows that the mantle is not completely rigid - acts as a very thick - viscous - liquid 1021 times as thick as motor oil.

Explains why contents have roots under mountain belts

Post glacial uplift of Scandinavia

Earth's internal heat

Temperatures in the Earth - geotherm and why inner core is solid

Conduction vs convection

models of mantle convection - single versus double layer

Magnetic field of the Earth - geomagnetism and paleomagnetism

Paleomagnetism

Fossil magnetism -

thermal remanent magnetism - igneous rock

Depositional remanent magnetism - sedimentary rocks

Geomagnetic Reversals

Magnetic stratigraphy