Origin Of Universe, Solar System, Earth
Origin of the Universe
Event that led to the formation of the Universe1500 - 2000 Ma. At that
moment, all matter was compressed into a space billions of times smaller
than a proton. Both time and space were set to zero. (Without space there
can be no time in the space-time continuum of Einstein's theory of relativity).
Since that moment galaxies have been moving away from each other, and the
universe has been expanding.
Evidence for Big Bang
Both pieces of evidence have been used to back calculate the age of the
The universe is expanding - (Edwin Hubble, 1929) Observed a Red
Shift when looking at the spectrum light coming from distant galaxies.
All light from these galaxies is shifted towards longer wavelengths, i.e..
toward red light. This is the Doppler effect, and could only occur
if the galaxies were moving away from each other at very high speeds. In
fact they are moving away from each other at a rate proportional to the
distance between them.
Analogies for Doppler effect - change in frequency of any wave (sound/light)
that is caused by movement of the source relative to the observer
Sound waves - car horn, train whistle. Train moves toward you, sound waves
are compressed - higher pitch. Train moves away, sound waves stretched
- lower pitch.
Raisins in a rising loaf of bread. Start a cm apart. After an hour, its
nearest neighbor is 2 cm away (2 cm/hr), and the next raisin over is 4
cm away (4 cm/hr). To maintain regular spacing w/ expansion, speeds must
be directly proportional to distance.
Pervasive 3K background radiation (Penzias and Wilson) detected
radio waves at a frequency that correlates to radiation near absolute zero.
This was attributed to the fading afterglow of the Big Bang.
Expansion Rate - Astronomer's use red shifts to measure the expansion
rate of the universe. From this rate they back calculate to figure out
how long ago all the galaxies were at a single point (i.e.. time 0). This
gives and estimate for the age of the universe at 1500-2000 m.y.
Order of Events
Big Bang (infinitely small universe)
Four basic forces (Gravity/Electromagnetic/Strong+Weak Nuclear) United
(Physics as we know it does not exist)
10-43 seconds: gravity separates from four basic forces
Physics as we know it begins
T= 1032 K; Universe is expanding- now 10-28 cm diam.
10-35 -10-32 seconds: inflationary period
Strong nuclear forces separate out
Quarks/electrons & antimatter form
T= 1027 K; 30 cm diam. (Homogenous opaque stew?)
10-6 seconds: T cooled to 1013 K; size = solar system
Quarks combine to form protons/neutrons
Matter/antimatter collide and annihilate each other
Light excess of matter allows some to survive
This forms universe as we know it.
1 second: electromagnetic and weak nuclear forces have separated
180 seconds: T cooled to 109 K allowing protons & neutrons
100,000 yr.: T= 3000 K
Electrons combine with nuclei- create whole H/He atoms
Photons separate from matter-universe transparent to light
Liberation of photons observed as present day 3 K background
105-9 yr.: universe becomes clumpy - galaxies/stars form
Heavier elements generated by fusion in stars (B-Fe) and in nova/super
nova explosions (>Fe) of Population II stars. These are then re-incorporated
into new second generation (Population I) stars forming from the remaining
H/He and star dust (e.g.. Sun).
Formation Of Solar System
Any theory for the origin of the solar system, must explain the main observable
features of the solar system:
All planets revolve around Sun counterclockwise
All planets except Venus rotate on axis counterclockwise
All planets orbits lie in plane of ecliptic
Axes of planets except Uranus & Pluto perpendicular to ecliptic
Compositional variation (Inner planets - Terrestrial; Outer planets - Gaseous)
Rene Descartes (1644) - Solar system formed from gigantic whirlpool within
a universal fluid- eddies in flow produced planets
Kant/Laplace (1755) - Nebular Theory - rotating cloud of gas
Spinning cloud flattens to disk/concentric rings to form planets.
Explains why all planets revolve and rotate in counterclockwise direction
within the ecliptic plane
Flaw: Law of conservation of angular momentum indicates that the Sun would
have to rotate more rapidly than it does (25 days) after collapse of the
primeval dust cloud
Buffon (1745) - Comet passed close to Sun, pulling off matter which accreted
to form planets.
Moulton/Chamberlin (1900) - star passed close to Sun, pulling away huge
filaments of material that accreted to form planetismals.
Problems: such events are extremely rare. Also material is so hot that
it would dissipate into space and not accrete.
Solar Nebula Theory (Current Theory)
The solar system formed 4.6 Ga when interstellar material in a spiral arm
of Milky Way Galaxy condensed and collapsed. Under influence of gravity
this material flattened into a counterclockwise rotating disk
90% mass is concentrated in the center with rest occurring in solar nebula.
Compression at center raised T > 106 K- Sun formed when H/He
Turbulence/eddies in solar nebula led to formation of planetismals
Anomalous rotation directions/axis tilts explained by collisions between
planetismals as planets formed
Compositional variation among planets is related to distance from Sun-
Hot inner portion of nebula, rock and metallic elements condensed out first,
at high T. - Result: inner planets are "terrestrial" in composition.
Outer portion of nebula is cooler, so gaseous phases such as H, He, methane,
ammonia condensed out. Result outer planets are "Jovian" in composition.
Suns magnetic field interacted strongly with ionized nebular gases- resulted
in loss of solar rotational speed.
Early in life, Sun emitted a large blast which blew away uncondensed material.
Asteroid belt formed because tremendous gravitational field of Jupiter
prevented planetismals from accreting into a planet.
Origin And Differentiation Of Early Earth
Need to explain present density distributions within the Earth
Start with a cool and solidified Earth of uniform composition
Compression & short-lived radioactive isotopes heat interior
Heavy metals (Fe/Ni) melt and sink to the core
Light elements (Ca/Na/K) and silicates float to form mantle and crust
Problem: Unlikely that enough heat could be generated to remelt the Earth
At present, scientists are still divided over which model is correct.
Core/mantle/crust condensed in sequence
Ni/Fe condense at higher T than silicates to form the core
Ca/Na/K, silicates condense at slightly lower T to form mantle and crust
Meteorites and the Great Meteorite Shower
Meteorites are material left over from creation of the solar system and
have ages of 4.4 - 4.6 Ga.
For the first 700 Ma, Earth must have been subjected to major
period of meteorite bombardment as the solar system was cleared of remaining
pieces of solid material not already assimilated into planets or moons.
Evidence for this comes from the moon.
By inference, the Earth must have gone through a similar experience. Unfortunately,
the action of plate tectonics and erosion has erased any record of this
event. We see only a few impact sites preserved on Earth.
Lunar maria are huge basalt flows, probably representing impact scars of
Rest of moon scarred by smaller craters.
Dates of rocks associated with large lunar craters are 4-4.6 b.y.
Meteor impacts have occurred at a much lower rate since the early Archean.
However, major impact events have been called upon as a mechanism for triggering
Age of the Earth
Formation of the Earth
Earth's age: ~4.6 billion years old
oldest rocks ~3.8 billion years old
Q: How do we know these ages?
The Earth's age has been revised over the years:
"The world was created in 3963 B.C."
- Philip Melanchthon 1497-1560
"Heaven and earth, center and circumference, were created together,
in the same instant, and clouds of water . . . This work took place
and man was created . . . on the 17th of September 3928 B.C. at 9 o'clock
in the morning.
- Dr. John Lightfoot, Vice-chancellor of the University of Cambridge, 1642
"In the beginning God created Heaven and Earth, Gen. I, V. 1., which
beginning of time, according to our Chronologie, fell upon the entrance
of night preceding the twenty-third day of Octob. in the year of the Julian
Calendar, 710 [i.e., 4004 B.C.]"
- Archbishop James Ussher of Armagh 1658
This isn't to say that early attempts to estimate the age of the Earth
were wrong. Early attempts didn't know many of the things that we
currently understand about the Earth.
1785: James Hutton, Scottish geologist, Theory of the Earth maintained
present is the key to the past (uniformitarianism)
Demanded that the earth was more than 6000 years old
1899: Joly used the concentration of salt in sea water
Hutton said that processes that were occurring today have occurred
in the past and will continue to occur in the future at roughly the same
rate - hence his Principle of Uniformitarianism can be paraphrased
as the present is the key to the past.
1) early oceans were not salty
2) salt from the earth carried to the oceans in solution
3) present rate is previous rate (uniformitarianism)
age: ~100 million years old
1862-1897: Lord Kelvin (Thompson) estimated age of Earth based on
loss from an early molten Earth.
age: 20-40 million years old
Discovery of radioactivity (1895) invalidated Kelvin's estimate.
Absolute vs. relative
Absolute age dating is a method in which the actual age of something
Absolute methods include:
isotopic dating: using the natural, constant radioactive decay
of isotopes. For example, a given amount of 14C will decay
by half every ~5568 years into 14N. Therefore, by measuring
how much 14N is present, we can estimate how long it took to
Relative age dating methods just give us a sense that one thing
is older than another.
Relative age dating techniques include:
Law of Superposition
Accretion and Formation of the Earth
Bombardment of planetismals -> heating and accretion
Gravitational compression -> heating
Radioactive heating -> heating (homogenous, undifferentiated planet, T~1000*C)
Fe catastrophe -> differentiation
Magma ocean -> leads to formation of atmosphere and proto-continents
Continental differentiation -> chemical zonation
Last modified 1/9/01