LECTURE OBJECTIVE:

1. To discuss the evolution of life on Earth up to to first abundant appearance of fossil invertebrate organisms (e.g. echinoids, pelecypods, arthropods, porifera, etc.).

2. To determine major controls on the rate of evolutionary diversification.

• power of reproduction
• locomotion
• response to stimuli internal chemical activity and generation of energy

• 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
• 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
• Amino Acids formed naturally: The Miller Experiment
• Next linkage of amino acids into larger organic molecule chains called polymers
• Linking amino acids formed proteins
• formation of proteinoids, etc.
• The problem of replication: 3 theories
1. Fox: proteins came first, and tended to attract nucleic acids. But today, only nucleic acids can reproduce.
2. nucleic acids (single strand RNA) came first.
3. Cairns-Smith: Replication was first by a clay template followed by a genetic takeover event by nucleic acids
4. Wachtershauser: pyrite template in the reducing environments of hot deep-sea volcanic events
• positive surface charge attracks nucleic acids
• environment shield from cosmic radiation and impacts
• bacteria use hydrogen sulfide or methane as source of hydrogen, rather than water
• new studies of the genes of bacteria (by Carl Woese) in hot, salty springs or on methane/hydrogen sulfide reveal that they are among the most primitive organisms alive. Named them as a separate kingdom, the Archaebacteria
• life may have had its origins in hot springs or sulfide rich volcanic vents

• New fossil evidence since 1950's gives witness to three key events in early organic evolution
• the oldest fossils are 3.46 B.Y. (Warrawoonna Group, NW Australia)
• 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.

A. FIRST LIFE

• microscopic
• single cell
• heterotrophic (required external food source)
• lived in the ocean
• perhaps resembled the modern coccoid bacteria

• arose quickly - otherwise the heterotrophs would have "gobbled up all the goodies" and died, unless sulfide based
• 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?

• Blue-green algae or cyanobacteria, (no cell nucleus- prokaryotes, no specialized cell organelles, contains chlorophyll for photosynthesis)
• photosynthesis: CO₂ + H₂0 + light = (CH₂0) + H₂0
• 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

 

 
 
 

Successful Biosynthesis

• no fossil evidence of first heterotrophs
• fossils of successors, the photosynthesizing autotrophs provides proof of prior biosynthesis
• oldest fossils life found in Australia and southern Africa
• oldest fossils are 3.46 billion years old
• non-colonial, unicellular, <1 micron (a micron is 1/1,000,000 of a meter
• some bacteria-like
• some photosynthesizing organisms - evidence from chemical breakdown products of photosynthesis
• North Pole, Western Australia, 3.5 b.y. cyanobacteria
• Pilbara Shield, W. Australia, 3.4-3.5 b.y.
• stromatolites (laminar, organic sedimentary structures formed by cyanobacteria trapping calcium carbonate particles. Still living in a few environments today. Became abundant at 2.8 b.y.
• Stomatolites are the only megascopic fossils from 3.5 B.Y. to 700 Ma.

• Gunflint Iron Formation, W. Ontario - Lake Superior
• Age: 1.9 - 2.3 or 2.5 B.Y., therefore, approximately 2.0 B.Y.
1. bacteria
2. algae
3. filamentuous organisms
4. 8 genera, 12 species with a variety of form and function

• allows for exchange of genetic material and increase in diversity.
• may have arisen from a symbiotic association of prokaryotes (Lynn Margulis):
• anerobic bacteria become mitochondria
• spirochaetes become flagellum
• cyanobacteria become chloroplasts
• mitochrondria and chloroplasts now have their own genetic material, ribosomes, and are affected by antibiotics even wile the cell is not
• Bitter Springs Formation
• 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. (recent older find in Australia)
• much larger cells (60-200 microns, some 1mm) than typical small prokaryotes
• may be arcritarchs
• low diversity until 1.2 B.Y.
• corresponds to the first cycsts of acritarchs

• Note the first occurrence of diverse magascopic invertebrates are about 650 m.y. old