The Exam results …. Note: Ex1 score = (number correct)/49 You get one ‘bonus’ question due to boo-boo on a question in the 3PMer’s test

The Earth How it got this way ….

Accretion of planetesimals

(4.54 billion years ago) Massive enough to form a sphere START

Accretion of planetesimals Gravitational and impact energies melts it Temp. and pressure increase inwards to the core

Differentiation Denser materials sink Less-dense ones float IRON CORE MANTEL “Solid” crust Maybe only 10 million years later Liquid Fe core + rotation = magnetic field

Must have looked like this …

After some cooling IRON CORE MANTEL Lithosphere “cool, rigid rock”

Meanwhile: “Heavy bombardment period ” IRON CORE MANTEL Comets – ICE (water!) First few hundred-million years Asteroids Still cooling, Heavy cratering and Volcanism

Opps! IRON CORE MANTEL “Theia” (more than 4.4 billion years ago) Moon forms from the less- dense outer layers that get blasted off

After some major recovery …. Late bombardment tapers off IRON CORE MANTEL First oceans form about 3.8 billion years ago from comet water!

Note: close moon

After A LONG time …. The present IRON CORE MANTEL Lithosphere “cool, rigid rock” Convective cooling by the mantel driven by temp. difference 100 million year time scale. (bottom to top)

Tectonic plates

Tectonic activity

Our Atmosphere How it got this way ….

Volcanism! Gasses trapped within earth’s mantel released Liquid water!!!

Were did they all go? Were did this come from?

The light stuff: H 2 and He drifted off into space. (Low mass -> high speeds > escape velocity) Were did they all go? The semi-light stuff: CH 3 and NH 3 broken down in the atmosphere by UV radiation. (No ozone layer back then!!) Water and CO 2 ?? We get very lucky… Greenhouse gasses!

Temperature warm&cool enough for water to condense and rain! OCEANS! CO 2 the dissolves in the seas and is locked away in carbonate rocks (e.g. limestone)

Were did The O 2 come from? Modern stromatolites at Shark Bay, Western Australia. Stromatolites are rock structures built up by layers of cyanobacteria, microorganisms that contribute to the addition of O2 to the atmosphere. Their role in oxygen production dates back billions of years and similar structures to the stromatolites at Shark Bay have been found in rocks as old as 3.5 billion years before present.

Our oxygen is “plant” excretion

Atmospheric cycles – delicate balance of everything

“We’re so lucky” slide: Earth big enough: Earth-Sun distance just right: Slower cooling -- Fe core still molten producing a magnetic field protects us from solar ion wind We formed just far enough so water would condense, but not freeze. We owe the greenhouse effect for this! Avoided bad greenhouse by locking most H 2 O and then CO 2 in the oceans Liquid oceans form the right place for early anaerobic life to evolve. At first O 2 was a toxic waste product, building up. O 3 layer which shields later, land-based life from UV. Later life evolved to burn O 2 as food.

The “Green-house” effect

Why does something (i.e. a planet) change its temperature?

Energy inEnergy out T IF Energy in Energy out > Temperature increases!

Energy inEnergy out T IF Energy in Energy out < Temperature decreases!

Energy inEnergy out T IF Energy in Energy out = Temperature constant! EQULIBRIUM

After billions of years cooling, the planets are very near equilibrium! Only cooling very slowly (if at all)

T A planet at (surface) temperature T

T Solar radiation: This is ‘mostly’ in the visible range ENERGY IN Reflected (Albedo) Absorbed Sun Light Depends on surface composition Cloud reflectivity etc. Self heating: Radioactive decay! Decreases with time!

T Thermal radiation: For (modern) planetary temperatures, This is in the infra-red ENERGY OUT

SURFACE AT TEMPERATURE T

No atmosphere: All IR out to space.

SURFACE AT TEMPERATURE T Non-greenhouse atmosphere: Gasses do NOT absorb in the IR All IR out to space. N2N2 O2O2 Ar

SURFACE AT TEMPERATURE T With a greenhouse atmosphere: Gasses do absorb in the IR Less IR out to space. CO 2 H2OH2O Absorbed Re-emitted

For systems close to equilibrium, small changes in the energy balance can cause the surface temperature/climate to change New sources of CO 2 -> “run away” greenhouse effect. (cooling system failure) Nuclear war/asteroid strike -> “Nuclear winter”. (heating system failure) (increased albedo)