Origin Of Universe, Solar System, Earth

Origin of the Universe

Big Bang

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 universe.

 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

Formation Of Solar System

Any theory for the origin of the solar system, must explain the main observable features of the solar system:

Evolutionary Theories

Catastrophic Theories

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

Origin And Differentiation Of Early Earth

Need to explain present density distributions within the Earth

Homogeneous Accretion

Inhomogeneous Accretion

At present, scientists are still divided over which model is correct.

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.

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

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
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.
1899: Joly used the concentration of salt in sea water
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.

Age Dating

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:

Law of Superposition
Cross-cutting Relationships

Accretion and Formation of the Earth

Last modified 1/9/01