TOPIC 1 - INTRODUCTION

Organization of the Earth Sciences

What are the Earth Sciences?

Geology (solid Earth)

Oceanography(oceans)

Meteorology &Climatology(atmosphere)

Hydrology (dynamics of water on and within the Earth)

Scientists looking at these things need to know the composition (chemistry), physical nature, age etc to be able to work out where these things came from. Has it always been the same? Or has it evolved, and if so how?

Carl Sagan: "the only planet that we will ever live on"

This being the case we should know something about it

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The Earth - some very basic facts

The neighborhood - the Solar system

One of 9 planets:

Mercury, Venus, Earth, Mars (Asteroids), Jupiter, Saturn, Uranus, Neptune, Pluto (Fig 1.3)

Shape and Size of the Earth

Roughly spherical with a radius of 6370 Km (1.6 km = 1 mile so is about 4000 miles). Actually is an ellipsoid, and radius is slightly smaller at poles than equator

[ Measured by Eratosthenes about 200BC - librarian in Alexandria}

Age of the Earth

4,600 million years

Mass of the Earth

Mass of Earth 5.98 x 1024 Kg

This means that the average density is 5500 kg/m3 Rocks at the surface of the Earth have a density of only 2700-3000 kg/m3

? What does this mean? That more dense materials must lie at depth

Roughness of the Earths surface

Relief; ocean basins 5000 m (up to 10,000 m).Mountains up to 10,000 m

Oceans and Atmosphere

Talking of oceans, Earth is characterized by large amounts of H2O on its surface - much more than any other planet ~ 70% of the surface covered by ocean - accident of distance from sun - water exists in all three states.

Ice caps at the poles, liquid water and atmospheric water.

Thick atmosphere less than Venus, but more than Mars or the moon

20% Oxygen 80% Nitrogen trace amounts of CO2, H2O, Ar etc. gets thinner as go upward.

Oxygen points to presence of life on the planet

How did all these things come about? Origin of the Earth

Nebular-planetismal hypothesis.

Nebula - interstellar dust clouds - debris of exploded stars

Condensation of the nebula to planetismal stage. Planetismals collide - large planets sweep up smaller planets - many impacts (moon surface as evidence). This generates heat

A large impact of a Mars sized body would create huge amounts of heat - enough to melt a sizeable volume of the Earth. Thought now that such an impact occurred between 4400 and 4560 million years ago

Debris of impact formed the Moon, impact caused melting that formed magma and differentation of the Earth occured. Dense materials sank to center, light rose to surface - this occured about 4.2 billion.

Origin of Oceans and atmosphere

Some of magma erupted to surface, but contained dissolved gases and fluids. Thus, the original atmosphere consisted of nitrogen, carbon dioxide, water - common gases from volcanoes. Water condenses to form oceans

Oxygen? probably later in history with evolution of life. Evidence of bacteria etc back to 3500 Ma Certainly algae (primitive plants) were around by 2500 Ma. Photosynthesis (CO2 +sunlight -> energy = oxygen as a by- product

Present internal structure of the Earth.

Plate tectonics

Lots of left over energy from that early impact. Problem is how to cool the interior of the Earth - conduction - not efficient

Convection - flowing of soft material rising of hot material to surface.

This results in motion of hot "skin" overlying the mobile mantle

Mobile mantle is called asthenosphere

Skin is called lithosphere. (lithosphere is top 100km of mantle plus the crust) This lithosphere is not continuous - broken into lithospheric plates.

Plate boundaries

Divergent, mid ocean ridge, where most of heat lost

Convergent: subduction zones where lithosphere sinks into aesthenosphere

Transform: where edges of plates slide by each other. For exampleSan Andreas fault system in California

What do geoscientists do?

Scholarly research - understanding how the Earth works

Environmental protection - groundwater, surface water, landslides, earthquakes, volcanic eruptions, ocean currents, global warming

Engineering - road construction, dams, bridges

Searching for resources - petroleum, minerals