Transcript Origin of the Universe

Origin of the Universe
Understanding Earth’s uniqueness
Planetary evolution
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Where does water come from?
Why do we have oceans?
Why do we have life as we know it?
Elemental composition
Present day configuration relative to origins
Hydrological cycle
Dissolved gases/Ocean and Atmosphere
How did the earth become
habitable?
• How did Earth evolve?
• What makes it different from other planets?
Origin of the universe
• Importance of time scales
• Forces at work in the past – some changes as
planet evolved
• Forces at work today
• How can we measure age of the earth
How old is Earth?
• Biblical scholars of 19th century (Bishop Ussher) –
6000 years (started at 4004 BC)
• Classical Greeks – infinite – history endlessly repeats
itself
• Mayans believed earth recycled on a 3000 year time
scale
• Han Chinese thought earth was recreated every
23,639,040 years
• The age we now except may change but is consistent
with current theory
More recent efforts
• Lord Kelvin - 80 million years old – based on
cooling of molten Earth
• Darwin - really old based on time for natural
selection (biological argument)
• Hutton – really old based on uniformitarianism
(processes in the past taking place at rates
comparable to today) (geological argument)
Earth’s age
• Earth is about 4.5 (or 4.6) BY old
• First 700 MY Earth was a spinning cloud of gas,
dust and planetoids
• These condensed and settled to solidify into a
series of planets
• Since that time, geological history and evolution
commenced.
Formerly “oldest life”
Oldest life?
The Big Bang Theory
• Currently the dominant theory
• First iteration proposed by Georges Lemaître in 1927.
He observed the red shift in distant nebulas and invoked
relativity.
• Hubble found experimental evidence (1929) – galaxies
are moving away from us with speeds proportional to
their distance.
• Theory suggested because it explains the expansion &
predicts the existence of cosmic radiation (leftover
photons) & nucleosynthesis
• 1964 cosmic radiation discovered (Arno Penzias &
Robert Wilson who won the Nobel Prize)
Big Bang – what is it?
• Collapsing cloud of interstellar dust
• Cloud dense and cold so collapses under its own selfgravity (cold gas has less internal pressure to counteract
gravity)
• Once collapsed, it immediately warms up because of
release of gravitational energy during collapse
• All mass and energy concentrated at a geometric point
Big Bang
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~14 or 15 BY ago
Beginning of space and time
Expansion/cooling of universe began
Protons and neutrons form
Cooling initiated the formation of atoms – first
mostly H (the most abundant form of matter in the
universe) and He (two lightest elements)
The universe
• H2 and He gas are still the dominant elements in
the universe
– Still about 99% of all material
• Giant gas and dust clouds form
– Clouds begin to break into megaclouds
– Megaclouds organized into spiral and elliptical shapes
due to rotational forces
– Galaxies or nebulae are the gases and dust in the disk
• Some of the gas in these galaxies broke up into
smaller clusters to form stars
– Gravitational collapse of stars produces heat
– Initiates fusion reactions that make other elements
The Eagle Nebula from the
Hubble telescope
Interstellar clouds
Formation of galaxy and stars
• Galaxy – rotating aggregation of stars, dust, gas and
debris held together by gravity
• Stars are massive spheres of incandescent gases
• 100’s of billions of galaxies in the universe and 100’s
of billions of stars in the galaxies
• Sun is a star
• Sun plus its family of planets is our solar system
• Our solar system formed about 5 BY ago
• Our galaxy is out in a spiral arm
• Our solar system orbits the galaxy’s core
– (230 million year orbit at 280 km/s)
Formation of the Sun
• Clouds in interstellar space are many 1000’s of
times the mass of the sun
• Clouds contract, producing smaller fragments
• Form 1 or more star – depending how fast the
cloud fragment is rotating (faster yields more
stars)
The disk around the star Beta Pictoris as seen from
the Hubble Space Telescope) – real and false color
Stars
• Stars form in nebulae, large diffuse clouds of dust and
gas.
• Condensation theory – spinning nebula starts to shrink
and heat under its own gravity
• Protostar – condensed gases
• At temperature of ~10 million degrees C, nuclear fusion
begins (H’s fuse to form He) which releases energy and
stops shrinkage
• Star is stable once fusion reactions begin (form atoms
as heavy as C and O)
Our sun
in 5 by
Our sun
eventually
Star classification – most fall along main sequence band and are “normal”
Effective radiating temperature calculated using Wein’s law
Brightest bluest and most massive are O and B, early type stars (left)
Dimmest, reddest and least massive are K and M, late type stars
Our sun is a G2 star
Element synthesis
• Series of fusion reactions producing
elements up to Fe
• Fusion reactions convert a small amount of
mass to heat
– Heats up star
– Increases stars density
• Combine to increase core temperature
Beginning of the end
• Star starts consuming heavier atoms increasing
energy output and swelling to a “red giant”
• Nuclear fuel in core is spent
• Incinerates planet and throws off matter
including heavy elements
• More massive stars get hotter and consume H at
higher rates and make heavier atoms (e.g., Fe)
The end
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H is consumed
Core collapses on itself
Internal temperatures sore so can no longer contract
Star implodes
Cataclysmic expansion called a supernova (30 sec)
Mass is accelerated outward
Forces holding apart atomic nuclei are overcome
Produces free neutrons
Heavier atoms formed by neutron capture
Heavy elements
• Reactions produce stable and radioactive
elements
• Radioactive elements important for
planetary evolution
– Internal heat source driving plate tectonics
• Elemental composition
Abundance of Fe
• Fe is abundant in cores of stars that explode
• Nuclear physics dictates that this element is the
most stable element that can form via fusion
reactions
– Formation of other elements requires fission reactions
or reactions with free neutrons
• Fe accumulates in the core before it explodes
• Other lower mass elements occur in supernovae
debris since core is still burning other elements
• General decrease in elemental abundance up to Fe
and accumulation of Fe
Our Solar System
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Our solar nebula was struck by a supernova
Caused our condensing nebula to spin
Introduced heavy atoms to seed the formation of planets
5 BY ago, the solar nebula was 75% H, 23% He and 2%
other material
• Center became protosun
• Outer material became planets – smaller bodies that
orbit a star but do not shine by their own light
Chemical composition of Sun
• Our sun did not form early after the big bang
• Contains elements that could only form during
death of a red giant (elements beyond Fe)
• Gasses and dust from explosion of a red giant
condensed to form our sun
• Same material that formed the sun also formed the
planets
– Earth and terrestrial planets are also predominantly Fe,
Mg, Si, and O
Our solar system
• Most of the material in the cloud that formed our
sun ended up in the sun
– Chemical elements in sun similar to elements in
universe
• Some material ended up in the nebular disk around
the sun
– Formed planets, moon, asteroids, comets
• This material was different in chemical
composition
– Elements that were contained in dust and ice formed
planets
• Gasses not retained by sun were largely lost
– Exception is some of the large, gassy outer planets
Planets
• Grew by accretion – big clumps use gravitational pull to accrete condensing
matter
• Near sun, first materials to solidify had higher boiling points (metals and
rocky minerals) – Mercury is mostly Fe, Ni. Inner rocky planets.
• Next Mg, Si, H2O and O2 condensed (plus some Fe and Ni). Middle planets
(e.g., Earth).
• CH4 and NH3 in frigid outer zones. Outer gassy planets (Jupiter, Saturn,
Uranus and Neptune).
Stabilization of solar system
• Protosun became star (sun) and nuclear fusion began
• Solar wind (radiation) at the start of those reactions
cleared excess particles and ended rapid accretion of
inner planets.
Our solar system
• Collapse of nebular cloud that had been hit by a red
giant to form our sun
• Nuclear reactions commenced
• Chemical fractionation of planets circling new sun
• Hot inner region of the ring
– Loss of volative elements
– Inner planets retained metals and oxides that can condense
at high temperatures
• Cold outer region of the ring
– Accumulation of ices and gasses
– Gasses accumulated in large outer planets because their
cores accreted fairly early and their gravitational attraction
due to their masses was sufficient to retain gases.
Terrestrial planets
• Mercury, Venus, Earth and Mars
• Nuclear physics sets relative abundance of
elements and inorganic chemistry controls the
chemical forms of these elements
• Elements that form gasses largely lost from
planets as compared to chondrites
• Elements forming oxides largely retained
– Some loss due to volatilization
– Chondrites – found in meteors and thought to represent
original material that formed the planets
• Oxygen and sulfur are exceptions – have gaseous
and solid forms
Early Earth
• Homogeneous throughout during initial accretion of cold particles
• Surface heated by impacts (asteroids, comets and debris) – first 500 my
• Heat, gravitational compression, radioactive decay caused partial melting.
• Density stratification.
Gravity pulled heavy
elements to interior.
• Friction during this
produced more heat.
• Lighter minerals (Si,
Mg, Al and O-bonded
compounds) migrated to
surface forming Earth’s
crust.
Timeline (since big bang)
• 10-35 sec ABB (The Big Bang)
– The universe is an infinitely dense, hot fireball.
• 10-6 sec ABB (1 millionth of a second)
– Universe forms: Expansion slows down; universe cools and
becomes less dense
– The most basic forces in nature become distinct: first gravity,
then the strong force, which holds nuclei of atoms together,
followed by the weak and electromagnetic forces. By the first
second, the universe is made up of fundamental particles and
energy: quarks, electrons, photons, neutrinos and less familiar
types. These particles smash together to form protons and
neutrons.
• 3 sec ABB
– Formation of basic elements
– Protons and neutrons come together to form the nuclei of
simple elements: hydrogen (1 proton), helium (2 protons) and
lithium (3 protons) (1, 2 and 3 in periodic table). It will take
another 300,000 years for electrons to be captured into orbits
around these nuclei to form stable atoms.
• 10,000 yr ABB
– Radiation Era
– The first major era in the history of the universe is one in
which most of the energy is in the form of radiation -different wavelengths of light, X rays, radio waves and
ultraviolet rays. This energy is the remnant of the primordial
fireball, and as the universe expands, the waves of radiation
are stretched and diluted until today, they make up the faint
glow of microwaves which bathe the entire universe.
• 300,000 yr ABB
– Matter dominates
– The energy in matter and the energy in radiation are equal. As
universe expands, waves of light are stretched to lower and
lower energy, while the matter travels onward largely
unaffected. Neutral atoms are formed as electrons link up with
hydrogen and helium nuclei. Microwave background
radiation gives us a direct picture of how matter was
distributed at this early time.
• 300 MY ABB
– Birth of stars and galaxies.
– Gravity amplifies slight irregularities in the density of the
primordial gas. Even as the universe continues to expand
rapidly, pockets of gas become more and more dense. Stars
ignite within these pockets, and groups of stars become the
earliest galaxies. (Still perhaps 12 to 15 billion years before
the present).
• 5 BY ago Birth of the Sun
– The sun forms within a cloud of gas in a spiral arm of the Milky Way Galaxy.
A vast disk of gas and debris that swirls around this new star gives birth to
planets, moons, and asteroids . Earth is the third planet out.
– The image on the left, from the Hubble Space Telescope, shows a
newborn star in the Orion Nebula surrounded by a disk of dust and gas
that may one day collapse into planets, moons and asteroids.
• 3.8 BY ago Earliest Life
– The Earth has cooled and an atmosphere develops. Microscopic living
cells, neither plants nor animals, begin to evolve and flourish in earth's
many volcanic environments.
• 700 MY ago Primitive Animals appear
– These are mostly flatworms, jellyfish and algae. By 570 million years
before the present, large numbers of creatures with hard shells suddenly
appear.
• 200 MY ago Mammals appear
– The first mammals evolved from a class of reptiles that evolved
mammalian traits, such as a segmented jaw and a series of bones that
make up the inner ear.
• 65 MY ago Dinosaurs become extinct
– An asteroid or comet slams into the northern part of the Yucatan Peninsula
in Mexico. This world-wide cataclysm brings to an end the long age of the
dinosaurs, and allows mammals to diversify and expand their ranges.
• 600,000 yr ago Homo sapiens evolve
– Our earliest ancestors evolve in Africa from a line of creatures that
descended from apes.
• 170,000 yr ago Supernova 1987a explodes
– A star explodes in a dwarf galaxy known as the Large Magellanic
Cloud that lies just beyond the Milky Way. The star, known in
modern times as Sanduleak 69-202, is a blue supergiant 25 times
more massive than our Sun. Such explosions distribute all the
common elements such as Oxygen, Carbon, Nitrogen, Calcium and
Iron into interstellar space where they enrich clouds of Hydrogen
and Helium that are about to form new stars. They also create the
heavier elements (such as gold, silver, lead, and uranium) and
distribute these as well. Their remnants generate the cosmic rays
which lead to mutation and evolution in living cells. These
supernovae, then, are key to the evolution of the Universe and to life
itself.
• 1054 Crab Supernova appears
– A new star in the constellation Taurus outshines Venus. Chinese, Japanese,
and Native American observers record the appearance of a supernova. It is
not, however, recorded in Europe, most likely as a consequence of lack of
study of nature during the Dark Ages. The remnants of this explosion are
visible today as the Crab Nebula. Within the nebula, astronomers have
found a pulsar, the ultra-dense remains of a star that blew up.
• 1609 Galileo builds first telescope
– Five years after the appearance of the great supernova of 1604, Galileo
builds his first telescope. He sees the moons of Jupiter, Saturn's rings, the
phases of Venus, and the stars in the Milky Way.
• 1665 Newton describes gravity
» At the age of 23, young Isaac Newton realizes that gravitational
force accounts for falling bodies on earth as well as the motion of
the moon and the planets in orbit. This is a revolutionary step in the
history of thought, as it extends the influence of earthly behavior to
the realm of the heavens. One set of laws, discovered and tested on
our planet, will be seen to govern the entire universe.
• 1905 Einstein’s Theory of Relativity
Relativity recognizes the speed of light as the
absolute speed limit in the universe and, as such,
unites the previously separate concepts of space
and time into a unified spacetime. Eleven years
later, his General Theory of Relativity replaces
Newton's model of gravity with one in which the
gravitational force is interpreted as the response
of bodies to distortions in spacetime which matter
itself creates. Predictions of black holes and an
expanding Universe are immediate consequences of
this revolutionary theory which remains unchallenged today
as our description of
the cosmos.
• 1929 Hubble discovers universe is expanding
– Edwin Hubble discovers that the universe is expanding. The astronomer
Edwin Hubble uses the new 100-inch telescope on Mt. Wilson in Southern
California to discover that the farther away a galaxy is, the more its light is
shifted to the red. And the redder a galaxy's light, the faster it is moving away
from us. By describing this "Doppler shift," Hubble proves that the universe
is not static, but is expanding in all directions. He also discovers that galaxies
are much further away than anyone had thought.
• 1960 Quasars discovered
– Allan Sandage and Thomas Matthews find sources of intense radio energy,
calling them Quasi Stellar Radio Sources. Four years later, Maarten
Schmidt would discover that these sources lie at the edge of the visible
universe. In recent years, astronomers have realized that they are gigantic
black holes at the centers of young galaxies into which matter is heated to
high temperatures and glows brightly as it rushes in.
• 1964 Microwave radiation discovered
– Scientists at the Bell Telephone Laboratories discovered microwave
radiation that bathes the earth from all directions in space. This radiation is
the afterglow of the Big Bang.
• 1967 Discovery of Pulsars
– A graduate student, Jocelyn Bell, and her professor, Anthony
Hewish, discover intense pulsating sources of radio energy,
known as pulsars. Pulsars were the first known examples of
neutron stars, extremely dense objects that form in the wake
of some supernovae. The crab pulsar, is the remnant of the
bright supernova recorded by Native Americans and cultures
around the world in the year 1054 A.D.
• 1987 Light from supernova 1987 reaches Earth
– The light from this supernova reaches earth, 170,000 years
after is parent star exploded. Underground sensors in the
United States and Japan first detect a wave of subatomic
particles known as neutrinos from the explosion. Astronomers
rush to telescopes in the southern hemisphere to study the
progress of the explosion and perfect models describing the
violent deaths of large stars.
• 1990 Hubble launched
– The twelve-ton telescope, equipped with a 94-inch mirror, is
sent into orbit by astronauts aboard the space shuttle
Discovery. Within two months, a flaw in its mirror is
discovered, placing in jeopardy the largest investment ever in
astronomy.
• 1990 Big Bang confirmed
– Astronomers use the new Cosmic Background Explorer
satellite (COBE) to take a detailed spectrum of the microwave
background radiation. These studies showed that the radiation
is in nearly perfect agreement with the Big Bang theory. Two
years later, scientists used the same instrument to discover
minute variations in the background radiation: the earliest
known evidence of structure in the universe.
• 1993 Hubble optics repaired
– Hubble's greatest legacy so far: detailed images of galaxies
near the limits of the visible universe.
• 100 Trillion
Future
– Astronomers assume that the universe will gradually wither
away, provided it keeps on expanding and does not recollapse
under the pull of its own gravity. During the Stelliferous Era,
from 10,000 years to 100 trillion years after the Big Bang,
most of the energy generated by the universe is in the form of
stars burning hydrogen and other elements in their cores.
• 1037 yrs
– Most of the mass that we can currently see in the universe is
locked up in degenerate stars, those that have blown up and
collapsed into black holes and neutron stars, or have withered
into white dwarfs. Energy in this era is generated through
proton decay and particle annihilation.
• 1038 to 10100 The Black Hole Era
– After the epoch of proton decay, the only stellar-like objects
remaining are black holes of widely disparate masses, which
are actively evaporating during this era.
• 10100 Dark Era Begins
– At this late time, protons have decayed and black holes have
evaporated.Only the waste products from these processes
remain: mostly photons of colossal wavelength, neutrinos,
electrons, and positrons. For all intents and purposes, the
universe as we know it has dissipated.
From: PBS Online (http://www.pbs.org/deepspace/timeline/)
Aging the Earth & Solar System
• Oldest rocks on earth about 4.1 bybp (zircons)
• Material in solar system appears older (~4.55 bybp)
• Dating meteorites, chunks of rock and metal, formed
about the same time as the sun and planets and from the
same cloud.
– Carbonaceous chondrites are a class of meteorites believed to
be the most primitive in the solar system (silicate minerals,
water and carbon)
• Dating moon rocks and oldest rocks found on Earth
(about 3.8 BY old)
• Rate of expansion (2002, astronomers had very accurate
measurements and calculated backwards to an age of 1314 BY old).
How do we age things?
• Isotopic decay
• Radioisotopes are unstable and decay to form
daughter products which form next to parent
nuclide.
• Know the ratio of daughter to parent in
undisturbed sample and the rate of conversion
(e.g., decay rate or half-life) allows computation
of age
• This has been done with several isotope pairs to
arrive at age of solar system
Isotopes
• The ordinary isotope of hydrogen, H, is known as Protium, the other
two isotopes are Deuterium (a proton and a neutron; stable) and
Tritium (a protron and two neutrons; unstable). Hydrogen is the only
element whose isotopes have been given different names.
• Radioactive decay – spontaneous disintegration of unstable nuclei
• For low atomic number elements stable is about 1:1 neutrons:protons
in the nuclei. For higher atomic number elements, the ratio is about
1.6:1.
• Heavy nuclides (atomic number > 82) have no stable configuration.
• Different types of decay
• FYI: Fusion of hydrogen into helium provides the energy of the
hydrogen bomb
Some isotopes
Parent isotope
Daughter Isotope
Half Life
238U
235U
232Th
87Rb
40K
39Ar
14C
147Sm
206Pb
207Pb
208Pb
87Sr
40Ar
39K
14N
147Nd
4.47 x 109 years
7.04 x 108 yrs
1.40 x 1010 yrs
4.88 x 1010 yrs
1.25 x 109 yrs
269 yrs
5,730 yrs
1.06 x 1011 yrs
*daughters are smaller and contain fewer protons, neutrons & electrons
Date chondritic meteorites
Pb isochron approach
-pairs of isotopes for relativity
Timeclocks set at point of
crystalization
Earth formed over time period
as solar material accumulates
in planet as dust, rock and
planetessimals; this took 10 –
100 my (based on calculations)
Doppler shifting
• Wavelengths emitted by objects moving away are
shifted to lower frequency (towards reds)
• Wavelengths emitted by objects moving towards
us are shifted to higher frequency.
• Example of sound – pitch of fire engine is higher
as truck moves towards you and lower as it moves
away)
• For galaxies outside our group, the redshift is
known as hubble expansion (after Edwin Hubble
who discovered this phenomenon in 1929).
Another way to look at time
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0-7 No record (no baby pics)
8-12 First rocks formed that are preserved today
12 First living cell appeared
22-23 Oxygen appeared
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Atmosphere becomes oxygenated
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First fossils formed (earlier records are dubious)
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First vertebrates
41.7 First land plants
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First reptiles
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First flowering plants
45.6 Mammals, birds, insects became dominant
25 days ago First human ancestors
0.5 hours ago Civilization began
1 min ago Industrial revolution began
Geologic Time – Appendix II
The origin of life
Next time
Emerging field
• Exobiology
– Carbonaceous chondrites
– Primordial soup
– Reducing environments
– polymerization
• Composition of a cell
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59% H
24% O
11% C
4% N
2% Others (P, S, etc)
• Composition of a cell
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50% protein
15% nucleic acid
15% carbohydrates
10% lipids
10% other