DISTANCES FOR EARTH ISSUES:

> RADIUS (6371 KM)> PLATE THICKNESS

(100 KM)> TOPOGRAPHY (0-10 KM)

(MILE = 1.6 KM)

TIME - MILLIONS TO BILLIONS OF YEARS

> AGE OF UNIVERSE (SINCE BIG BANG) 15 Byr

> AGE OF EARTH 4.6 Byr

> AGE OF OLDEST OCEAN 200 Myr

DISTANCE & TIME SCALES IN GEOLOGY DIFFER FROM DAILY LIFE

ABSOLUTE AGES FROM RADIOACTIVE DECAY

RELATIVE AGES FROM ROCK STRATA AND FOSSILS

Length scales from very very small to very very large in geology

>Galaxy- 1019 m>Solar System 1013 m >Earth 107 m >Mountain 104 m >Rock 10-1 m >Atom 10-10 m in nucleus

Davidson 1.1

SIZE OF EARTH DETERMINED BY ERATOSTHENES 200 BC

SUMMER SOLSTICE AT NOON IN EGYPT SUN'S RAYSDIRECTLY INTO WELL AT SYENE (ASWAN)AT 7.2O ANGLE IN ALEXANDRIA, 787 KM TO NORTH

CIRCUMFERENCE FROM:7.2 / 360 = 787 / CIRCUMFERENCECIRCUMFERENCE= 39,350 KM

CIRCUMFERENCE = 2 * * RADIUS =3.14159) RADIUS = 6263 KMCLOSE TO CORRECT VALUE OF 6371 KM!

ISOTOPES

atomic nucleus has positively charged protons (p) and neutrally charged neutrons (n) orbited by negatively charged electrons (e)

element defined by atomic number - number of protonsdifferent isotopes have different numbers of neutrons

and so different atomic weights (# n + p)

example: carbon - atomic number 6carbon 12 carbon 13 carbon 14

some isotopes are radioactive or unstable -neutron decays into proton plus electron

carbon 14 -> nitrogen 14 + electron6p, 8n 7p, 7n e

CARBON DATING

is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C) formed in the

upper atmosphere by the effect of cosmic ray neutrons upon nitrogen

14. The reaction is:14N + n => 14C + p

where n is a neutron and p is a proton

AFTER DEATH, 14C => 14N + electron (beta particle)

SO THE AMOUNT OF CARBON-14 DECREASES WITH TIME

AND TELLS WHEN DEATH OCCURRED

IN TIME EQUAL TO ONE HALFLIFE, HALF THE PARENT ISOTOPE DECAYS

AMOUNT REMAINING GIVES AGE

Davidson 6.17

RADIOACTIVE DATING METHODS

1/2 PARENT ISOTOPE DECAYS IN HALF-LIFE

ONLY USEFUL FOR ABOUT 10 HALF-LIVES (otherwise not enough left)

CARBON -> NITROGEN DATING - HALF-LIFE 5750 yrs - GOOD TO ABOUT 57,000 yrs - short compared to most geological time scales.

Hence used some in geology, more in archeology

OTHER ISOTOPIC METHODS:

RUBIDIUM --> STRONTIUM HALF-LIFE 57 Billion yr (Byr)

POTASSIUM --> ARGON HALF-LIFE 12 Byr

URANIUM --> LEAD HALF-LIFE 4.5Byr ; 713 Myr

NOTE: These reactions give off lots of energy, and are important for heating the earth. The last is the nuclear reactor & atomic bomb reaction.

MASS SPECTROMETER

SEPARATE ISOTOPES OF DIFFERENT MASSES

ANOLOGY: IF WIND BLOWS ON A MOVING BOWLING BALL AND FEATHER, PERPENDICULAR TO THEIR PATH, THE LIGHTER FEATHER IS

DEFLECTED BUT THE HEAVIER BOWLING BALL CONTINUES ON ITS ORIGINAL PATH

REAL MASS SPECTROMETER

SEPARATE ISOTOPES OF DIFFERENT MASSES USING

MAGNETIC FIELD

OUTPUT: PEAKS SHOWING ABUNDANCES OF DIFFERENT ISOTOPES

RELATIVE AGES FROM ROCK STRATA AND FOSSILS 

EVEN BEFORE ABSOLUTE DATING DISCOVERED, GEOLOGISTS KNEW EARTH WAS VERY OLD

HUTTON (1780's) REVOLUTIONIZED SCIENCE BY REALIZING MILLIONS OF YEARS NEEDED FOR SLOW ACCUMULATION OF SEDIMENTS (sand, etc) TO BUILD UP THICK ROCK LAYERS

ROCKS SHOWED "UNIFORMITARIANISM" - TODAY'S PROCESSES WERE SIMILAR IN PAST - INSTEAD OF

"CATASTROPHISM" WHICH ASSUMED EXTRAORDINARY EVENTS (BIBLICAL FLOOD, etc) A SHORT TIME (thousands of

years) AGO

ROCK STRATA CAN BE TRACED OVER LARGE DISTANCES, SO THEIR POSITIONS CAN BE USED TO ESTABLISH RELATIVE

AGES AND HISTORY OF EVENTS

FOSSILS IN ROCKS CAN BE USED AS MARKERS AND GIVE RELATIVE AGES

NOTE: DISCOVERY OF LONG GEOLOGIC TIME AND BIOLOGICAL EVOLUTION WERE RELATED 

Davidison 6.5

ROCK RECORD SHOWS GEOLOGIC HISTORY

Deposition Deformation Uplift & erosion

Subsidence; new rock deposited above

Tilting, uplift & erosion

Sicar point, Scotland

EARTH 4.6 BILLION YEARS OLD

Hard to relate to human time

Davidson 1.21

Earliest hominids (“Lucy” 3 Mybp

Modern humans 100,000 yr

GEOLOGIC TIME SCALE

Davidson 6.15

Smithsonian website

Earth’s Plate Tectonics Future- The Movie

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The Periodic Table (Simplified)

HOW DID THE EARTH’S MATERIAL ARISE?

HOW DID IT FORM THE PRESENT EARTH?

Material in house vs building of house

THE ELEMENTS FORMED BY NUCLEAR REACTIONS IN STARS AND SUPERNOVAS (NUCLEOSYNTHESIS)

THE SOLAR SYSTEM FORMED BY THE CONDENSATION OF THE SOLAR NEBULA - A GAS CLOUD

THE PLANETS ACCRETED FROM THE NEBULA AS SMALL PLANETESIMALS CLUMPED UP

THESE "PROTOPLANETS" HEATED UP AND DIFFERENTIATED AS THE DENSE MATERIAL SANK TO THE CENTER, GIVING THE ROCKY CRUST AND MANTLE AND THE IRON CORE

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COOLING CONTINUES TODAY AS CONVECTION AND PLATE TECTONICS

THE EXTENT TO WHICH CONVECTION CONTINUES CAUSES THE DIFFERENCES BETWEEN EARTH (active), MARS (dead), VENUS (in between?), MERCURY (dead)

Mars

CLIFF NOTES

Davidson 2.29

Davidson 2.29

WILKINSON MICROWAVE ANISOTROPY PROBE"BABY PICTURE" OF THE UNIVERSE

WMAP orbits four times farther than the Moon and a

million miles from Earth.

WMAP looks back to the first light in the Universe, the afterglow of the Big Bang (far left) that emerged 380,000 years after the Big Bang. This light took over 13 billion years to reach us. During that time, giant gas clouds (left side) condensed under the force of gravity to form the first stars (200 million years after the Big Bang). Then, galaxies and galaxy clusters formed into the structure we see today (right side). The temperature fluctuations in the WMAP image correspond to seeds that grew to become galaxies.

NASA

BIG BANG OCCURRED ABOUT 15 BILLION YEARS AGO  

Wilkinson Microwave Anisotropy Probe- Microwave (radio wave) light from 380,000 years after the Big

Bang

Shows seeds that generated today’s cosmic structure

> like a picture of an 80 year old on the day of their birth.

> patterns are small temperature differences.

> "warmer" (red) and "cooler" (blue) spots

> today 2.73 degrees K background temperature

NASA

Frame one shows temperature fluctuations (color differences) in the oldest light in the universe, seen today by WMAP. Temperature fluctuations arose from the slight clumping of material in the infant Universe, which ultimately led to the structures of galaxies we see today.

Frame two shows matter condensing as gravity pulls matter from regions of lower density onto regions of higher density.

Frame three captures the era of the first stars, 200 million years after the Big Bang. Gas has condensed and heated up to temperatures high enough to initiate nuclear fusion, the engine of the stars.

Frame four shows more stars turning on. Galaxy chains forms along those filaments first seen in frame two, a web of structure.

Frame five depicts the modern era, billions upon billions of stars and galaxies... all from the seeds planted in the infant Universe.

NASA

HUBBLE SPACE TELESCOPE

2.4 m (94.5 in.) smooth polished mirror, weighs 1,800 pounds

Above blurring effects of Earth’s atmosphere;

10-20 times better than ground-based telescopes

Resolve astronomical objects with angular size of 0.05 arc seconds (=seeing pair of fireflies in Tokyo from Maryland)

NASA

Because it is outside our atmosphere, the telescope can view astronomical objects

across a broad swath of the electromagnetic spectrum, from ultraviolet light, to visible, to

near-infrared wavelengths.

Mission cost to date $14B

STARS AND PLANETS EVOLVE FROM A NEBULA- A GAS CLOUD

Hubble Space Telescope view of Orion Nebula- shows 5 young stars surrounded by gas and dust

“We are all star-stuff”

NASA

NUCLEOSYNTHESIS I: HYDROGEN "BURNING" (PROTON-PROTON CHAIN)

Forming helium from hydrogen gives off lots ofenergy (a natural hydrogen bomb).

Nucleosynthesis requires very high temperature*. The minimum temperature for hydrogen fusion is 5 million degrees.

*An atomic bomb is needed to set off a hydrogen bomb

Star (like our sun)'s energy comes from combining light elements into heavier elements by fusion, or "nuclear burning"

Hydrogen “burning” =fusion of 4 hydrogen nuclei (protons) into helium nucleus (2 protons + 2 neutrons)

NUCLEOSYNTHESIS II: LATER "BURNING"

STAGES

Forming elements with more protons requires higher temperatures- carbon requires about one billion degrees - Most heavy elements, from oxygen up through iron probably produced in stars ten times larger than our Sun.

> After hydrogen exhausted, the star "burns" helium to form progressively heavier elements, carbon and oxygen, … until iron and nickel form.

> Stars are layered ("onion") with hottest "burning" deepest.

> Process releases energy so star keeps "burning".

NUCLEOSYNTHESIS III: SUPERNOVA EXPLOSIONS

Forming elements heavier than iron and nickel requires energy input.

Supernova explosions when massive stars have exhausted their fuel supplies in core & burned everything into iron and nickel.

The star then collapses & explodes.

Nuclei with mass heavier than nickel (gold, silver, lead, uranium, etc.) form in explosions over seconds, compared to the lighter ones that took billions of years to form, and are much rarer.Material thrown out into space May end up in later generation

stars and planetsCRAB NEBULA - the remnant of a star about 10

times the mass of our Sun that in 1054 exploded as a supernova

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CRAB NEBULA - the remnant of a star about 10 times the mass of our Sun that in 1054 exploded as a supernova

HUBBLE TELESCOPE VIEW

PLANETS FORMED AS PART OF THE LIFE CYCLE OF STAR FORMATION

Wood, The Solar System

SOLAR NEBULA

- Gas cloud contracts and heats up

- Hot flat disk forms with protosun at center

- As nebula cools, gas condenses

- Gas and dust form small chunks- planetesimals

- Planets accrete by collision and gravity

- Bigger ones grow at expense of others ("rich get richer"), leading to accretion of a few planets

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NEBULA TO SOLAR SYSTEM- THE MOVIE

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Determine element composition using:

> SPECTROSCOPY- FROM SUN LIGHT

> METEORITES THAT IMPACT ON EARTH

> EARTH’S ROCKS & PROPERTIES

CONCLUDE: SUN, EARTH, AND PLANETS FORMED (CONDENSED) FROM THE SOLAR NEBULA - THE ORIGINAL MATERIAL OF THE SOLAR SYSTEM

ABUNDANCES OF ELEMENTS- Similar relative amounts between the sun, meteorites and Earth

Davidson 2.10

Find Star’s composition from spectroscopy- Use light to identify elements

Davidson 2.4

Meteorite Impacts: Samples of the Solar System

Meteorites- oldest surviving rocks in our solar system

Asteriod Eros- 33-km long undifferentiated body

-Relative proportions of rock-forming elements similar to Sun

-Made of the same material as certain primitive meteorites

- Never subjected to the melting and the separation into compositionally distinct layers that Earth, Mercury, Venus and Mars experienced.

Near Earth Asteroid Rendezvous (NEAR)

Near Mission Descent

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THE SOLAR SYSTEM

> INNER, TERRESTRIAL (earthlike) PLANETS: MERCURY, VENUS, EARTH, MARS-FORMED IN HOT INNER PART OF NEBULA-- MADE OF DENSE ROCK & IRON

> OUTER, GIANT, PLANETS: JUPITER, SATURN, URANUS, NEPTUNE-FORMED IN COLD OUTER PART OF NEBULA-- MADE MOSTLY OF HYDROGEN, HELIUM, & LESS DENSE MATERIAL FROM NEBULA

THE EARLY EARTH AND MOON

Press & Siever