EARTH DIFFERENTIATES - EARLY EARTH UNIFORM (HOMOGENEOUS) - PLANET HEATS UP

EARTH DIFFERENTIATES- EARLY EARTH UNIFORM (HOMOGENEOUS)- PLANET HEATS UP- DENSE IRON CORE SINKS, LEAVING LAYERED PLANET: LIGHT CRUST ON TOP , CORE BELOW, AND MANTLE IN BETWEEN- DIFFERENTIATION CONTINUES TODAY AS PLANET COOLS BY THERMAL CONVECTION - PLATE TECTONICS-HENCE EARTH'S EVOLUTION IS CONTROLLED BY ITS THERMAL HISTORY- TEMPERATURE AS A FUNCTION OFDEPTH AND TIME ("HEAT IS THE GEOLOGICAL LIFEBLOOD OF PLANETS")

Press & Siever

HEAT (A FORM OF ENERGY) TRANSFER OCCURS BY

- RADIATION - HEAT TRANSFER BY ELECTROMAGNETIC WAVES (SUNLIGHT)

IMPORTANT AT EARTH SURFACE BUT NOT VERY EFFICIENT IN SOLID EARTH

- CONDUCTION - HEAT TRANSFER BY MOLECULES COLLIDING (TOUCH A HOT OR COLD OBJECT)

IMPORTANT IN SOLID EARTH BUT SLOW

- CONVECTION - HEAT TRANSFER BY MOTION OF MATERIAL (HOT AIR IS LESS DENSE THAN COLD, SO IT RISES)

IMPORTANT IN SOLID EARTH, OCEAN, AND ATMOSPHERE - MORE EFFICIENT THAN CONDUCTION

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ANALOGY: MONEY CAN BE TRANSFERRED ELECTRONICALLY (fast but easily disrupted), BY MAIL (slow), OR BY CARRYING BAGS OF CURRENCY

Davidson 2.25

IF WE HEAT A PAN OF WATER

FIRST GET SLOW HEAT TRANSFER BY CONDUCTION

LATER, ROLLING BOILING STARTS. FAST HEAT TRANSFER BY CONVECTION - MORE EFFICIENT

CONVECTION CELL

FLUID HEATED FROM BOTTOM

HOTTER, LESS DENSE, FLUID RISES & COOLS

COLDER, DENSER FLUID SINKS & WARMS

OCCURS BECAUSE FLUID EXPANDS WHEN HEATED & BECOMES LESS DENSE

Also happens in stars, ovens - anywhere a fluid is heated!

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CRUCIAL FOR UNDERSTANDING ATMOSPHERE (WEATHER), OCEAN (CURRENTS) & SOLID EARTH - BOTH IN MANTLE & CORE

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CONVECTION IN ATMOSPHERE

Sun heats earth’s surface

Warm moist air rises, cools, loses moisture (rain)

Cool dry air sinks

Davidson 1.15

Makes earth’s climate belts:

wet temperate zone (Chicago)

dry deserts (Arizona, Sahara)

wet tropics (near equator)

Colder in mountains, airplanes



PLATE TECTONICS AS CONVECTION

Plate tectonics is the surface manifestation of convection cells in earth’s mantle .

Ridges (spreading centers) mark upwelling, hot limbs.

Trenches (subduction zones) mark cold downwelling limbs.

Oceanic plates form at ridges, cool as they spread and move across the ocean basins, and heat up as they subduct.

More complicated than simple pot of water, but idea’s the same

EARTH'S HEAT ENGINE TODAY

CONVECTION IN ROCKY MANTLE CONVECTION IN LIQUID IRON OUTER CORE

SOLID INNER CORE FREEZES FROM LIQUID OUTER CORE

70% HEAT TRANSFER BY PLATE TECTONICS (CONVECTION THROUGH MANTLE)

25% CONDUCTION THROUGH CONTINENTS

5% (?) BY MANTLE PLUMES

Davidson 2.26

PLATE MOTIONS & PLANETARY EVOLUTION

> Plate motions from continuing evolution & differentiation from originally uniform planet to layered one

> Vertical movement of heat & material through time

> Lithosphere (plates)- cold strong outer boundary later of earth

Plate tectonics causes volcanism, that produces atmospheric gasses (carbon dioxide CO2 and water H2O) needed to support life and keep planet warm (“greenhouse effect”)

MAMMOTH LAKES, CA - PART OF LONG VALLEY CALDERA, ERUPTED 760,000 YEARS AGO - STILL ACTIVE

GAS KILLED TREES, SICKENED PEOPLE, CLOSED CAMPGROUND

VOLCANIC GAS

THE EARLY ATMOSPHERE

After Earth formed 4.5 Byr ago, gases accumulated from

volcanism and comet impacts.

Volcanic gases are very different than the present atmosphere:

mostly H2O (85%) and CO2 (10%), with some nitrogen and sulfur.

So the early atmosphere was probably H2O and CO2 with a bit

of nitrogen. Comets - more common then – probably

contributed significant H2O.

H2O and CO2 are efficient greenhouse gases, so 4 Byr

ago the earth was MUCH hotter than today.

PRIMEVAL ATMOSPHERE EVOLVED TO TODAY’S

1. H2O removed from the atmosphere by precipitation, ending up in oceans, lakes, etc.

2. CO2 removed by dissolving into rain > Dissolves into ocean waters> Reacts with carbon compounds to FORM sedimentary rocks

3. Later (about 2 BYr ago), photosynthesis from plants removed more CO2 & added oxygen

COMPARED TO ORIGINAL, TODAY'S ATMOSPHERE >MUCH less dense

>Nitrogen (a trace gas from volcanic eruptions) the most abundant gas

>Oxygen a major constituent (good for us)

Nitrogen - 78% Oxygen - 21%Carbon Dioxide - 0.03%Argon - 0.9%Trace Gasses (Ne, He, krypton, H2, ozone)Water Vapor - 0% - 4%

Composition persists due to PLATE TECTONICS (volcanism), RAIN, & LIFE

PRESENT EARTH'S ATMOSPHERE:

Requires temperatures for LIQUID WATER NOT TOO HOT, NOT TOO COLD

Venus too hot

Mars too cold

PLATE TECTONICS CAUSES VOLCANISM THAT PRODUCES ATMOSPHERIC GASSES (including carbon dioxide CO2 & water H2O)

THAT SUPPORT LIFE & KEEP PLANET WARM (GREENHOUSE)

NY Times

Short wavelength solar radiation passes through glass

Things in greenhouse absorb energy, heat up, & re-readiate longer wavelengths

Longer wavelengths can’t pass through glass

Greenhouse heats up

GREENHOUSE EFFECT

Davidson 15.27

GREENHOUSE EFFECT

>Some atmospheric gasses (including CO2, H2O, CH4) trap heat

>Earth's surface about 33oC warmer so life can thrive

Natural greenhouse effect keeps us alive

Increased greenhouse gasses due to human activity

>promote global warming >likely climate changes in precipitation, storm patterns, sea level, agriculture, etc…> Some win, some lose

GREENHOUSE GASSES

Incoming visible light from sun can pass through atmosphere

Water vapor and CO2

absorb outgoing (reradiated) longer wavelength radiation

Planet warms up

Fraction of light absorbed

Davidson 15.28

ELECTROMAGNETIC SPECTRUM

GLOBAL WARMING

Estimated changes in annual global mean temperatures and carbon dioxide concentrations over the past 137 years

relative to a 1961-90 base period.

Temperature data (deg C) go through 1996 (red line)

Carbon dioxide values are from ice cores until 1956 (blue dashed line) and from air sampling at Mauna Loa, Hawaii from

1957 through 1995 (blue solid line).

Arctic ice melting faster as temperatures rise

Satellite observations show sea ice in the Arctic melting faster while air temperatures

in the region are rising.Arctic sea ice extent has

dropped to 2.05 million sq. miles, the lowest in the

satellite record. Trend has various consequences, some bad, some good,

depending on one’s view

9/29/05

Walrus on melting ice basks in the sun in Chukchi Sea, between Alaska and Russia.



Melting of West Antarctic and Greenland ice sheets would raise sea level 10 or more meters

Red areas along gulf and east coasts would be flooded, affecting 25% of US population

Glaciers have been retreating rapidly. These are excellent monitors of climate change





If only the Greenland Ice Sheet melts, the impacts will be enormous. Red areas in this image of southern Florida show effects of a five-meter rise of sea level. Yellow areas denote urban locations.

Could global warming start a little Ice Age?

Heat transported north by warm surface water, released to atmosphere, keeps climate moderate (Gulf Stream)

Cold, saltier, denser deep water flows south

Melting of northern hemisphere ice sheet and glaciers could release lots of fresh water, lower density of southward flow, shut down conveyer

Northern hemisphere would get colder

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COMPARISON OF TERRESTRIAL PLANETS

-ON EARTH DIFFERENTIATION CONTINUES TODAY AS PLANET COOLS BY THERMAL CONVECTION - PLATE TECTONICS, SO PLANET IS "GEOLOGICALLY ALIVE"WITH MOUNTAIN BUILDING, EARTHQUAKES, VOLCANOES, ETC.

-MERCURY AND MARS ARE SMALLER PLANETS THAT LOSE HEAT FASTER (small cookies cool faster than large ones, small ice cubes melt faster than big ones, small animals have to eat almost all the time to keep alive - while big ones can sleep)

-THUS MERCURY AND MARS COOLING HAS GONE SO FAR THAT THEY HAVE THICK LITHOSPHERE AND ARE "GEOLOGICALLY DEAD”

- NOT CLEAR ABOUT VENUS

- EARTH IS "GEOLOGICALLY YOUNG" - MERCURY AND MARS ARE "GEOLOGICALLY OLD" - THOUGH THEY FORMED AT THE SAME TIME (dog years versus human years)


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Dense atmosphere (90 times Earth's) composed mostly of CO2 (carbon dioxide).

Thick clouds of sulfuric acid obscure the surface.

Atmosphere produces run-away greenhouse effect that raises Venus' surface temperature to over 450 deg C (hot enough to melt lead).

Venus' surface hotter than Mercury's despite being nearly twice as far from the Sun.

Venus probably once had lots of water like Earth that boiled away, leaving it quite dry.

Earth might be like this if it were a little closer to the Sun.

Not yet clear why Venus turned out so differently from Earth

VENUS - RUNAWAY GREENHOUSE

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MARS - TOO COLD & DRY NOW

VERY THIN ATMOSPHERE



MARS - LIQUID WATER IN PAST-SHOWN BY LANDFORMS & MINERALS

MARS CLIMATE CHANGED – PERHAPS MANY TIMES -BETWEEN HOT/WET PERIODS

GREENHOUSE GASSES KEPT PLANET WARM

WITHOUT ENOUGH GASSES: SURFACE TOO COLD FOR LIQUID WATER AND MOST LIFE (if ever existed)

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VENUS (TOO HOT), MARS (TOO COLD), & EARTH (JUST RIGHT) GOOD PLANETS - AND HENCE INTELLIGENT LIFE MAY BE RARE

EARTH CLIMATE VULNERABLE TO CHANGES THAT MIGHT MAKE IT SO HOT ("GREENHOUSE") OR SO COLD ("ICEHOUSE") TO SIGNIFICANTLY IMPACT CIVILIZATION

GOOD PLANETS ARE HARD TO FIND

HUMAN-TYPE LIFE REQUIRES NARROW RANGE OF CONDITIONS: TEMPERATURES (LIQUID WATER) & OXYGEN ATMOSPHERE

SUN, EARTH (PLATE TECTONICS), OCEANS, ATMOSPHERE, LIFE INTERACT IN COMPLICATED WAYS TO KEEP EARTH HABITABLE



Venus

Earth

Mars

EARTH DIFFERENTIATES - EARLY EARTH UNIFORM (HOMOGENEOUS) - PLANET HEATS UP

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