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

accretion 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

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

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???

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