Earth as a Planet

Lectures 1,2

When did the Earth form

4.5 billion years ago

What is the continental crust mostly made of

Granite

What is the oceanic crust mostly made of

Basalt

What is the core mostly made of

Iron and nickel

Characteristic of Lithosphere

Rock-like

Characteristic of asthenosphere

Semi-fluid

Which is thicker, continental or oceanic crust?

Continental crust

Which is denser, continental or oceanic crust?

Oceanic crust

Temperature of mantle asthenosphere

1500 degrees celcius

How deep is the Earth's mantle

2900km

How deep is the Earth's core

3470km

Convection currents definition

The movement of fluid and material caused by the uneven heating

What mineral is found in the mantle

Olivine

What is the surface of the crust made of

Quartz and feldspar

Characteristic of the outer core

Liquid, convecting rapidly

Characteristic of inner core

Solid

Principle of uniformitarianism

The principles we observe today are the same as those in the past

Principle of superposition

Younger rocks are deposited to overlie older rocks

Stratigraphy definition

The study of time sequences indicated by successions of rock strata

Principle of Original Horizontality

Layers of sediment are deposited in a horizontal position

Principle of cross-cutting relationships

A rock or fault is younger than any rock or fault through which it cuts

The Principle of Faunal Succession and Absolute Ages

Each bed or series of beds contains a characteristic assemblage of fossils

Principle of Lateral Continuity

Layers are continuous until encountering an obstruction

Principle of Inclusions

Objects enclosed in rock must be older than the time of rock formation

What type of rocks can trilobites be found in

Palaeozonic rocks

What type of rocks can dinosaurs be found in

Mesozoic rocks

What is an igneous rock

Rocks that have crystallised during cooling of magma

What is the oldest rock in Britain

Gneiss, 2.8 billion years old

What is a sedimentary rock

Rocks formed due to the weathering, erosion and re-deposition of material from pre-existing rocks

What is a metamorphic rock

Rocks that have been recrystallised from igneous/sedimentary rocks due to changes in temperature and pressure

How thick is the oceanic crust

5 - 15km

How thick is the continental crust

30 - 70km

Definition of topography

The study of land surface

Definition of stratigraphy

The study of rock layers and layering

What is stratification

Layering

What is a morain

Rock formed under an ice glacier

Where do earthquakes happen

Narrow zones between tectonic plates

How does ice appear on satellite images

Smooth

What is happening as the earth rotates over 100,000 years

It is wobbling which changes sea level

What does it mean for the Earth to be an oblate spheroid

Slightly flattened at the poles

Length of Earth's polar radius

6357km

Length of Earth's equatorial radius

6378km

How far into the Earth have humans observed

12.5km using a borehole

Density of sandstone

1.9 - 2.4g/cm 3

Density of limestone

1.9 - 2.7g/cm 3

Density of granite

2.6 - 2.7 g/cm 3

Density of basalt

2.8 - 3g/cm 3

Definition of epicentre

Point on the surface directly above the focus of an Earthquake

Primary wave definition

Waves transmitted by vibrations oscillating in the direction of propagation (push/pull)

Secondary wave definition

Vibrate at right angles to the direction of propagation

Can S waves be trasmitted through liquid

No, S waves cannot because liquids have no elastic strength

What does a seismometer do

Measures vertical displacement during an earthquake

Definition of refraction

A wave bends as it enters a medium of a different density

Where does the Earth increase in density

The density of the Earth increases with depth

What governs wave velocity

density, compressibility, rigidity

At what distance from the epicentre are no S-waves recorded

103 degrees - must be liquid

Why does the outer core have lower P-wave velocity than the mantle

Between 103 and 142 degrees, no strong P-waves were recorded because they cannot be refracted. They appear again at >186 degrees.

Why is it believed that the inner core is solid

Weak P-waves arrive between 103 - 142 degrees

What is the MOHO

Mohorovicic discontinuity

Who discovered the MOHO

Mohorovicic in 20th century

What happens to MOHO in mountainous areas

Gets pushed down

How was the MOHO discovered

There was a double return of P-waves

How do modern seismologists determine the Earths structure

By using artificial explosions

How deep is the MOHO under oceanic crust

5 - 15km

How deep is the MOHO under mountain belts

50 - 70km

Definition of orogeny

The earth's crust is folded and deformed by converging plates to form a mountain range

Definition of tomography

The properties of seismic waves are modified by the material through which they travel

What is the density like when the mantle is cool

High density with fast P and S waves

What is the density like when the mantle is hot

Low density with slow P and S waves

What colour are fast seisimic velocities (+0.8%)

Blue

What colour are low seismic velocities (-0.8%)

Red

Where is the MOHO

The base of the crust

What is the subduction zone

The mantle lithosphere penetrates the mantle asthenosphere by getting pushed under it