Origin Of Universe, Solar System, Earth

Origin of the Universe

Big Bang

Evidence for Big Bang

• 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 to fuse
• H and He nuclei formed
• 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
• 10^5-9 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

• 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)

Evolutionary Theories

• 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

Catastrophic Theories

• 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)

• 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 burning initiated.
• 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

Homogeneous Accretion

• 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

Inhomogeneous Accretion

• 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

 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.

• Lunar maria are huge basalt flows, probably representing impact scars of huge meteorites.
• 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 extinction events.

Age 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
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 heat

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 is determined.
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 form.

Relative age dating methods just give us a sense that one thing is older than another.
Relative age dating techniques include:

flora
faunal
Law of Superposition
Cross-cutting Relationships
Paleomagnetic

• 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