Download RADIUS (6371 KM) - Department of Earth and Planetary Sciences

DISTANCE & TIME SCALES IN GEOLOGY DIFFER FROM DAILY LIFE
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
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 RAYS
DIRECTLY INTO WELL AT
SYENE (ASWAN)
AT 7.2O ANGLE IN ALEXANDRIA,
787 KM TO NORTH
CIRCUMFERENCE FROM:
7.2 / 360 = 787 / CIRCUMFERENCE
CIRCUMFERENCE= 39,350 KM
CIRCUMFERENCE = 2 *  * RADIUS
 =3.14159) RADIUS = 6263 KM
CLOSE 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 protons
different isotopes have different numbers of neutrons
and so different atomic weights (# n + p)
example: carbon - atomic number 6
carbon 12
carbon 13
carbon 14
some isotopes are radioactive or unstable neutron decays into proton plus electron
carbon 14 -> nitrogen 14 + electron
6p, 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
ROCK RECORD SHOWS GEOLOGIC HISTORY
Deposition
Deformation
Uplift & erosion
Subsidence;
new rock
deposited
above
Tilting, uplift &
erosion
Sicar point,
Scotland
Davidison
6.5
Earliest
hominids
(“Lucy” 3
Mybp
Modern humans
100,000 yr
EARTH 4.6
BILLION YEARS
OLD
Hard to relate to
human time
Davidson 1.21
GEOLOGIC
TIME
SCALE
Davidson 6.15
Smithsonian website
Earth’s Plate Tectonics Future- The Movie
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Video decompressor
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HOW DID THE EARTH’S MATERIAL ARISE?
The Periodic Table (Simplified)
HOW DID IT FORM THE PRESENT EARTH?
Material in house vs building of house
CLIFF NOTES
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
Mars
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)
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Davidson 2.29
Davidson 2.29
WILKINSON MICROWAVE ANISOTROPY PROBE
"BABY P ICTURE" 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
> 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
Shows seeds that generated today’s cosmic structure
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)
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
NASA
STARS AND PLANETS EVOLVE FROM A NEBULA- A GAS CLOUD
Hubble
Space
Telescope
view of
Orion
Nebulashows 5
young stars
surrounded
by gas and
dust
“We are all
star-stuff”
NASA
NUCLEOSYNTHESIS I: HYDROGEN "BURNING" (PROTON-PROTON CHAIN)
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)
Forming helium from hydrogen gives off lots of
energy (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
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 planets
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
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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
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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ABUNDANCES OF ELEMENTS- Similar relative amounts
between the sun, meteorites and Earth
Determine element
composition using:
> SPECTROSCOPYFROM 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
Davidson 2.10
Find Star’s composition from spectroscopyUse light to identify elements
Davidson 2.4
Meteorite Impacts: Samples of the Solar System
Near Earth Asteroid Rendezvous (NEAR)
Meteorites- oldest surviving
rocks in our solar system
Asteriod Eros- 33-km long
undifferentiated body
-Relative proportions of rockforming 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 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