The sun provides the center of all life on earth, and is a primary driver of many geological processes. Thus the composition of the sun is very important to earth; it is the hydrogen (70%) fusing into helium (27%) that provides the energy.

The origin of the universe is, in part, detected by the red shift, which is the change that occurs to light from an object that is retreating from us rather rapidly. It indicates that the universe is rapidly expanding.

If all the stars are traced back to an original center, they all originated 15-18 billion years ago. This event was thought to have occurred in a "Big Bang". There are 3 possible models of the universe:

• Big bang, which ends with the galaxies disappearing somewhere out in the farther reaches of space
• Steady state cosmology, where the universe expands continuously, with new matter made continuously
• Oscillating universe where the big bang reverses and contracts in a 'big crunch"

There are several constraints on any theory for the origin of the solar system

1. Dynamic: Orbital constraints; the planets orbit in a prograde motion.
2. Compositional: The terrestrial planets are dense and rocky. The Jovian planets are composed primarily composed of hydrogen and helium.
3. Age: Maximum age of any rocks found is 4.6 billion years. This fits well with the age calculated for the sun.

The major features of the cold accretion model for the solar system (and Earth) is the 'swarming' of many smaller particles until a protoplanet formed. These rotated and swept away most of the debris in it's orbital path. This took an estimated 10 million years. These protoplanets eventually contracted and formed planets.

The earth, and the other planets, have experienced differentiation. To accomplish this the planet must be heated enough to become at least partially molten. This heat comes from 3 sources:

1. Accretionary heat
2. Radioactive decay
3. Gravitational compression
4. 
   

An alternate proposal for accretion is the hot model, which stipulates that the material gathering to form the planet was already hot. This means the solar nebula gases were very hot, possibly reaching temperatures of over 1,000C. The major advantage of this theory is that it allows differentiation to occur as the planet accretes.

Outgassing is the process by which gasses are released from the rocks that held them and then vented to the surface. This probably was mostly finished within the first billion years; this is supported by sedimentary rocks dating back 3.8 billion years.

Carbon dioxide, water were probably the primary gasses present in Earth's early atmosphere, with smaller amounts of hydrogen, carbon monoxide and hydrogen chloride.

The scarcity of inert gasses indicate that the gasses of earth were not the result of bombardment because that bombardment would have included the inert gasses, making our atmosphere richer in them.

The early atmosphere was reducing and nonoxygenic. The processes for origin of oxygen are photochemical dissociation and photosynthesis. Dissociation occurs in the upper atmosphere by light breaking apart water molecules.

There are a number of clues to the nature of the early atmosphere:

1. Before 3.5 billion years ago:

• sediments lack grains of oxidized iron--but pyrite was common
• lack of alkaline rocks such as dolomite and limestone indicates an acidic environment--which in turn indicated CO₂

1. Gradual addition of oxygen later in the Precambrian (3.0-1.8 by) indicated by the presence of BIF's which are banded iron formations.

• note that these are economically important, providing most of the iron mined in the world

1. For rocks younger than 1.8 by, free atmospheric oxygen is indicated by red shale, siltstones and sandstones.
2. By this time the relative absence of atmospheric CO₂ is indicated by the formation of carbonate rocks.

Ocean water thought to have been "sweated" from the earth's interior. The composition has been maintained relatively constant by the precipitation of surplus solutes. The evidence for nearly constant composition is marine fossils.

If this is true, it is important and surprising that the oceans:

1. Oceans produced very early
2. modern volcanoes do not add new water
3. constant volume troublesome (no new water from the mantle)

Precambrian rocks are:

• often crystaline
• few/no fossils
• used relative degree of metamorphised, but wrong
  • Note inference that rocks that experience the most metamorphism were likely to be the oldest.
• use radioactive dating to determine age
  • This now provides the sole basis for mapping Precambrian terranes and deciphering their geological history.
• Relative age can be determine by crosscutting relationships, inclusions

a. Within the first ~0.8 by after the origin of earth:

• Major outgassing
• Development of internal structure
• Oldest sediments occur

b. Origin of life: 3.8 by

1. Earliest BIF: ~3.0 by
2. Red beds and oldest glaciation about 2.0 by.
3. Significant bombardment by meteorites during the first by, but
   • destroyed by later episodes of melting and erosion
   • Proof is on the moon : )

All continents have shields (exposed areas of Precambrian rocks). There is no particular pattern to these. The Canadian shield is divided into Precambrian provinces on the basis of:

1. abrupt truncations in structural lineations
2. bands of severly deformed rocks of former orogenic belts.

These provinces were once separate crustal segments, bound together by belts of deformed rocks that mark their collisions.

Komatiites are ultramafic rocks formed when the surface patches of the magma ocean cooled. They reflect the higher temperature gradients that prevailed during the late Hadean, and represent a condition that no longer exists. Note that at first there was only oceanic crust. This is because the continental crust had not yet formed.

In general, there are two kinds of Archean rocks of the Canadian craton:

• Granulites -- metamorphosed intrusive rocks.
• Greenstone -- meatmorphosed extrusive rocks.

Pillow lavas are lavas that were extruded under water.

Apparently the Archean protocontinents were unlike the present continets: small, steep-sided, narrow with rugged shorelines.

Whereas volcanic arcs were the sites for the birth of ganulite associations, the back-arc basins were the probably location fo the development of greenstone belts.

S. Africa and Australia had large cratons (continental crust). This is important because there are very old sedimentary rocks present.

The Witwatersrand Supergroup of S. Africa is notable because it has very old streams and alluvial fans which have no iron pyrite--due to the lack of an oxygen atmosphere.
Origin of life:

1. Originated in the ocean
2. Solvent properties of water helped it develop
3. circulation of the ocean important
4. can only happen once

• food (roganic chemicals) present onl once.

Stanley Miller origionated experiments to create organic chemicals.

1. Gasses used: methane, ammonia, hydrogen and water vapor. Not used: carbon dioxide.
2. Energy source was simple organic molecules.
   • Other energy source: black smokers on the ocean floor
3. The products were complex organic compounds.

The importance of such studies is that it shows that life can be created.

Next step: amino acids combined into more complex structures (proteinoids) by heat. The possible locations for such heat treatment are anywhere volcanic activity is occuring.

And then proteinoids form tiny microspheres.

But: long-chain nucleic acids require polymerization (joining together); Clay minerals may serve as a catalyst for polymerization.

Life probably originated in the sea:

1. it contains the salts needed for health and growth.
2. Water is a universal solvent capable of dissolving a great variety of organic compounds
3. The ocean currents circulate and mix these compounds.

Life cannot originate today because there is no supply of energy compounds.

Life conventionally thought to have originated in shallow marine water. Recent alternatives proposed are hydrothermal vents. Even more recently faint light has been discovered there, raising the possibility of some kind of photosynthesis.

The first organisms were probably heterotrophs.

When available food (dissolved organic compounds of non-biologic origin) ran out, some form of food manufacture became necessary.

Several autotrophic pathways; the most important was that of photoautotrophism, capable of doing photosynthesis. This may be wrong; perhaps the first organism were autotrophs in thermal springs on the ocean floor.

Important things about oxygen:

1. it is toxic
2. oxygen metabolism is more efficient
3. protection from UV

Main differences between eukaryotes and prokaryotes:

1. cell size: pro much smaller
2. genetic organization: eu in nucleus
3. organelles: only eu have
4. reproduction: pro is only asexual

Sexual reproduction allows for the exchange of genetic information, which allows a much greater diversity and more rapid evolution.

Organelles in eukaryotic cells were once independent organisms that entered the eukaryotic cell and established symbiotic relationships with the primary cell. This theory is called the endosymbiotic theory. The differences between plants and animals is related to photosynthetic bacteria that became chloroplasts in plants.

Stromatolites are laminar, organic sedimentary structures formed by the trapping of sedimentary particles and precipitation of calcium carbonate in response to the metabolic activities and growth of matlike colonies of cyanobacteria. Recent work suggests that some of these layerd rocks were produced by non-biological processes (note that no actual cells are seen, just the layering). However, your text notes two lines of evidence supporting the presence of prokaryotes:

1. A variety of microfossils are found in them.
   • These are found in chert, which preserves soft-bodied creatures by replacement
2. C¹²/C¹³ ratios are preserved, providing evidence of biologic fixation of carbon dioxide by living organisms.

Characteristic economic minerals of the Archean:

1. gold, diamonds, iron, copper, chromium and nickel.
2. copper, zinc and iron that appear to have formed when sea water penetrated hot submarine lavas, extracting and then precipitating these as metallic sulfides on the sea floor.