The Big Bang…

– 13.7 billion years ago (13,700,000,000 yrs)

– Explosion so powerful that space itself was propelled outwards almost instantaneously

– 200 Million years later, the first stars formed

– Universe is still expanding today

The Sun and planets formed by accretion(smaller particles in the spinning nebular cloud clumping

together to form larger objects)

Formation of the Solar System: Nebular Hypothesis

Earth Accretion and “Iron Catastrophe”

Fig. 1.8, p. 8

(solid!)

Most of the water is here

We are here

Welcome to the Milky Way Galaxy

There was no oxygen (it would be made later by photosynthesis), and there were methane, ammonia, and high amounts of carbon dioxide.

The Early Atmosphere:Very Different Than Today’s

Defining the Marine Environment

A. 70.8% of the Earth’s surface is covered by the oceans – hence the “water planet”

1. 2/3 of the Earth’s land masses are in the Northern hemisphere, which is 61% ocean

2. 80% of the Southern hemisphere is ocean

B. 94% of the Earth’s eco-volume is in the ocean

C. 50% (or more) of the Earth’s photosynthesis occurs in the oceans

Geography of the Ocean Basins

• Oceans are traditionally classified into four large basins (doesn’t include Southern Ocean, listed in decreasing size).

• Pacific Ocean – largest and deepest• Atlantic Ocean • Indian Ocean• Arctic Ocean• Southern Ocean - the continuous body of water

which surrounds the Antarctic continent below 60°S latitude.

• Average depth is about 4,000m or 2.5 miles • Maximum depth of around 11,000 m (Mariana Trench

off the coast of Japan)

Differentiation of the Earth

(a) Early homogenous Earth (PROTOEARTH – 1000 times greater in diameter than Earth

(b) Lighter matter “floats” toward surface

(c) Modern structure of the Earth

• The Earth is density stratified, that is, each deeper layer is denser than the layer above.

• Mohorovicic Discontinuity (Moho) – density difference between the mantle and crust

Chemical Properties of Earth’s Layers Layer Chemical Properties Continental Crust Composed primarily of granite

density = 2.7 g/cm3 Oceanic Crust Composed primarily of basalt

density = 2.9 g/cm3 Mantle Composed of silicon, oxygen, iron and magnesium

density = 4.5 g/cm3 Core Composed mainly of iron

Density = 13 g/cm3

Cross-Section of the Earth

• Inner core - 1,200 km radius; 4,000°C (7,200°F); solid – too hot to be magnetic

• Outer core - 2,300 km radius, molten, rich in iron and magnesium, thought to generate the Earth’s magnetic field

• Mantle - thought to be solid, but near the melting point for most rocks, the mantle slowly swirls and mixes, 2,900 km radius

• Crust - outermost layer, solid, floats on the mantle, continental crusts and ocean crusts differ greatly, 4-60 km

Earth’s Composition

Earth’s Composition

Rocks• Igneous rocks – resolidification of magma

– Basalt (fine grained extrusive rock)– Granite (cools slower and forms crystals –

intrusive rock)• Sedimentary Rocks – formed by

weathered rocks– Quartz, sandstones, sand, gravel, silt, clay

• Metamorphic Rocks – formed by transformation of other rocks at temperatures greater than Earth’s surface– Marble, slate

• A cool, rigid, less dense layer (the lithosphere) floats on a hot, slowly-flowing, dense layer (the asthenosphere = upper mantle).

Why does it float???

Physical Properties of Earth’s Layers Layer Physical Properties Lithosphere The cool, rigid outer layer Asthenosphere Hot, partially melted layer which flows slowly Mantle Denser and more slowly flowing than the

asthenosphere Outer Core Dense, viscous liquid layer, extremely hot Inner Core Solid, very dense and extremely hot

Isostatic Equilibrium—gravitational equilibrium between the Earth’s lithosphere and asthenosphere

• Isostasis– force of gravity on crustal materials of varying densities… balance of mass!

• The concept of buoyancy is illustrated by a ship on the ocean. The ship sinks until it displaces a volume of water equal to the weight of the ship and its contents.

Layered Earth—Internal Heat

• Where does the heat within Earth’s layers come from?– Heat from within Earth keeps the asthenosphere

flowing. This allows the lithosphere to keep moving. The source of this heat is radioactive decay, given off when the nuclei of unstable forms of elements break apart.

• This heat travels in convection currents in the mantle.

Layers

• What evidence supports the idea that Earth has layers?– The behavior of seismic waves generated by

earthquakes give scientists some of the best evidence about the structure of Earth. Wave speed depends on what is traveled through—if it can travel through that medium.

• (above-left) S waves cannot penetrate Earth’s liquid core.

• (above-right) P waves are bent as they pass through the liquid outer core.

Oceanic versus Continental Crust

Oceanic crustal plates have a higher density and they are:

• Thinner• Geologically younger than continental

crust• Rich in iron and magnesium• Basalt, dark in color• Likely to sink

Oceanic versus Continental Crust

Continental crustal plates have a comparatively lower density and they are:

• Thicker• Geologically older than oceanic crusts• Rich in sodium, potassium, calcium, and

magnesium• Granite, lighter in color

Formation of the Oceans and Early Atmosphere

Figure 2 – 07

Volcanic outgassing

Recently some researchers have suggested that ice meteorites could have been an important source of water, although this view has been challenged.

Oceans = Volcanic Outgassing + Ice-Rich Comets

Fig. 1.12, p. 12

Where did Life Begin?

Cyanobacteria

The Origin of Life on Earth

• The earliest life forms probably arose in the oceans.

– Lightning? Hydrothermal vents? Outer space?

• The first fossil life forms are primitive bacteria found in rocks >3.5 billion years old! Animals and plants would evolve much later.

The Origin of Life on Earth

• Scientists have conducted experiments in which organic molecules have been synthesized under conditions thought to be similar to the early Earth and its atmosphere.

• Miller-Urey Experiment

A Timeline of Earth’s History

Humankind appears

Fig. 1.12, p. 12