I. SOURCE OF THE OCEANS: OUTGASSING OF THE EARTH

(Outgassing: the process by which water vapor and other gasses are released from the rocks that held them and then vented them to the surface)

Energy for outgassing supplied by:

- gravitational collapse

- volcanic outgassing

- meteorite and asteroid bombardment

Water from the mantle?

Mass of mantle = 4.5 x 1027 grams

Mass of oceans = 1.4 x 1024 grams

Therefore mantle must have lost 0.031% of its water

Is this reasonable? How much water in mantle?

Meteorites = 0.5% or 16 times water needed

When? -- Early! Oceans by 3.8 B.Y.

rapid formation because of greater volcanic activity in early earth history!

Outgassing could also addition of:

N, CO2, He, Ar, and H2O vapor to atmosphere

II. ATMOSPHERIC EVOLUTION

Age of earth 4.6 B.Y.

No rocks > 4.0 B.Y. therefore limits conjecture about early atmosphere and hydrosphere

Oldest rocks do indicate presence of atmosphere and hydrosphere

1st Atmosphere Probably similar to Jupiter which has retained greater share of original gas

CH4 methane

NH3 ammonia

H

He

Ne

Two major steps in further evolution

- both assume considerable loss of free H and He because of small atomic mass, what remained oxidized to form sea water

- greatest problem is explaining abundance of free oxygen on earth today!

2nd Atmosphere Formed by loss of H and He and chemical modification of original atmosphere

1. Dissociation of primeval water vapor into hydrogen and oxygen with most hydrogen escaping into space:

2H2O + uv light energy Æ 2H2 _ + O2

2. Newly freed oxygen reacted with methane to form carbon dioxide and more water vapor:

CH4 + 2O2 Æ CO2 + 2H2O

3. Oxygen would also react with ammonia to form nitrogen and water:

4NH3 + 3O2 Æ 2N2 + 6H2O

4. After all CH4 and NH3 were converted (by oxidation) to CO2 and N2 , then free O2 could accumulate as further dissociation of water vapor occurred.

- Earliest life probably anaerobic (living in oxygen free environment) and heterotropic (requiring external food source)

- Later oxygen-releasing photosynthesizers arose

-probably did not have advanced enzymes to rid self of oxygen

-use ferrous iron as an oxygen acceptor

therefore free oxygen first locked-up in formation of marine iron oxides

-origin of Banded Iron Formations! These are marine deposits of alternating rust red and gray bands. The red is due to ferric iron oxide (Fe2O3).

3 TO 1.8-2.0 B.Y. ago

- Evolution of oxygen and peroxide-mediating enzymes

- Spread of life in oceans

- O2 accumulates in the atmosphere

- Increased ultraviolet protection by ozone formation

(molecular oxygen O2 + atomic oxygen O = ozone O3)

oxidation of iron rich sediments exposed to atmosphere (on land) to formed. .RED BEDS beginning 1.8 to 2.0 B.Y. ago. The great RUST Event!

III. ORIGIN OF LIFE

Essential elements on early Earth: C, H, O, and N in universal solvent H2O

Arrangement of basic elements of life into more and more complex organic molecules to eventually form life

life = power of reproduction

locomotion

response to stimuli

internal chemical activity and generation of energy

DNA = code carrier which specifies making of proteins

RNA = carrier and genetic information to protein formers

- Key to origin of DNA, and thus life itself, is the natural synthesis of amino acids, which is the material from which larger proteins are made

- Next linkage of amino acids into larger molecules called proteinoids

Amino Acids formed naturally: The Miller Experiment

How and when did life originate?

- New fossil evidence since 1950's gives witness to three key events in early organic evolution

- This evidence comes from the PreCambrian, the oldest is 3.46 B.Y., NW Warrawoona Group)

- Life originated by gradual development of complex chemical environment through non-organic processes forming amino acids, sugars and other biologically important substances

- This stage of "chemical evolution" took millions of years for the elaboration, accumulation and differentiation of important chemical compounds (more later).

- Chemical evolution climaxed with chance assemblage of life-less organic molecules into living organisms.

FIRST LIFE.

microscopic

single cell

heterotrophic

lived in the ocean

perhaps resembled the modern coccoid bacteria

FIRST AUTOTROPH.

arose quickly - otherwise the heterotrophs would have "gobbled up all the goodies" and died

probably arose in response to organic nutrient depletion thus allowing the development of photosynthesizing autotrophs

- evidence for this are PreCambrian rocks which formed in the presence of free oxygen

What kind of autotrophs?

Bacteria no cell nucleus

Blue-green algae no specialized cell organelles

sexless

diffuse genetic material

no mitosis (body-cell division)

no meiosis (germ-cell division)

genetic conservatism - no gene

recombination therefore mutations damped out

With this background we will examine three important events of the PreCambrian evolution

I. Successful Biosynthesis

- no fossil evidence of first heterotrophs

- fossils of successors, the photosynthesizing autotrophs provides proof of prior biosynthesis

II. Threshold of Diversification

III. Development of the Eukaryotic Cell (with nucleus)

I. Successful Biosynthesis, oldest autotroph

- From Fig Tree Formation in Barberton Mts between Swaziland and S. Africa

- found in chert >3.2 B.Y. old (recent age 3.4 B.Y.)

- non-colonial, unicellular, <1 m

- bacteria-like, Eobacterium

- some photosyn. organisms - evidence from chemical breakdown products of photosynthesis

- North Pole, Western Australia, 3.5 b.y. blue-green algae

- Pilbara Shield, W. Australia, 3.4-3.5 b.y.

stromatolites (became abundant at 2.8 b.y.)

NOTE: Stomatolites are the only megascopic fossils from 3.5 B.Y. to 700 Ma. Stramatolites are laminar, organic sedimentary structures formed by cyanobacteria trapping calcium carbonate particles. Still living in a few environments today.

II. Threshold of Diversification

- Gunflint Iron Formation, W. Ontario - Lake Superior

- Age: 1.9 - 2.3 or 2.5 B.Y., therefore approximately 2.0 B.Y.

- bacteria

- algae

- filamentuous organisms

- 8 genera, 12 species with a variety of form and function

III. Development of Eukaryotic Cell (organisms with a definite nuclear wall, chromosomes, and the capacity for sexual reproduction).

- Bitter Springs Formation, N. Australia

- approximately 1 B.Y. old

- blue green algae and green algae

- fossils of well defined and dividing nucleus

- earliest may occur 1.75 B.Y.

- low diversity until 1.2 B.Y.

- allows for exchange of genetic material and increase in diversity.

Kingdom - Monera (no nucleus or chromosomes): Prokaryotic

- Bacteria

- Blue-green algae