The Fossil Record

How good is it?

Types of Fossils


Body Fossils - Remains of the whole body or parts of the body

Hard parts of the body are fossilized more readily than are soft however under the right kind of conditions soft tissues or their impressions can be preserved.  In some cases (e.g. clam shells) the hard parts are preserved in their original condition. However more often the original fossil is altered. There are three basic modes of fossilization


Trace Fossils - Indirect Evidence of Past Life

Burrows, tracks and trails,


Chemical signatures


Bias in the Fossil Record

Aquatic organisms

Since water is required for most types of fossilization organisms that live in the oceans or rivers tend to be preserved preferentially.

Mineralized body parts

Bones and shells preserve much better than do soft body parts. Hence we have excellent records for shelled marine invertebrates but  poor ones for terrestrial invertebrates like insects (Insects make up 75% of all living animal species but less than 1% of fossil species)


When fossilization occurred - The pull of the Present

Aging Fossils

Relative Age - Based upon Stratographic position

Absolute Age Based on Radiometric Dating


Geological Time Scale

See Table 6.1

Yes you are expected to know them


Plate Tectonics

The continents are not fixed they are moved by currents in the molten mantle

We can see the phenomenon of sea floor building in the mid-Atlantic and the effect of plates moving against each other in the action of the San Andreas Fault

The position of the continents has a major effect on the planetary climate. Central Pangaea was a very dry place.

The Present distribution of animals is in part a function of past continental drift

See Fig 7.22



The Origin of Life

A quick review


Chemical Evolution 4550-3800? Mya

Abiotic synthesis of Monomers

Miller-Urey Experiment 1953

Polymerization of Organic Monomers



Proteinoid microspheres



The RNA hypothesis

RNA nucleotides are concentrated in a saline solution they will self-assemble into an RNA polymer


Enzymatic Action


Achaean Era

3600- 2500 MYA


Tree of Life


The Earliest Living Things

What type of metabolism did the earliest forms of life have?

The oldest living things were simple prokaryotic cells which were heterotrophic and were anaerobic.


Types of Metabolism

Oldest Rocks

Isua, Greenland 3800 mya

12C to 13C ration in graphite suggests that it originated via photosynthesis

Warrawoona, Australia 3550 mya

Stromatolites - indicative of a shallow tidal environment or highly saline environment

Fig Tree Chert, South Africa 3400mya



Surprisingly the cyanobacteria in Stromatolites used photosynthesis based on H2O evolved about  billion years ago.  The "Calvin Cycle" using NADPH and ATP from the non-cyclical photophosphorylation is much more efficient than the more ancient anaerobic pathway.


Ancient Bacterial Blooms

Banded Iron Formations - These were initially thought to be indicative of atmospheric O2  the discovery of a group of ancient purple, non-sulfur bacteria in 1993 has changed the interpretation.

These bacteria use dissolved iron carbonate as a carbon source.


Archaebacteria (Archea)


Sewage Treatment Plants

 Hot Springs

 Oceanic Bottoms



Great Salt Lake, Dead Sea

Alkaline Lakes (pH 9.0)


 Hot Springs (<80C  pH < 2.0)

 Smoldering Gob Piles

Oceanic Bottoms




Purple Bacteria - mainly anaerobes use H2S as an electron donor

Chemoautotrophic Proteobacteria - mainly nitrogen fixers e.g. Rhizobium

Chemoheterotrophic Proteobacteria - enteric bacteria e.g. E. coli and Salmonella

Spirochetes- chemoheterotrophs, include free-living species, pathogens and symbioints.

Spirosymplokos forms microbial mats

Treponema pallidum  the cause of syphilis

Pillotonia found in the hind-gut of  of wood eating cockroaches and termite

Cyanobacteria - have plant like photosynthesis although some are also capable of utilizing H2S in high sulfur conditions.

Entophysalis colonial form that still produce stromatolites.

Nostoc obligate symbioints with fungi to form lichen.

Synechococcus nitrogen fixers

Saprospirae - fermenting gliders

Bacteroides  inhabit the human intestinal tract in large numbers anaerobes

Spirospira oxygen-respiring aerobes live in organic rich environments where they decay  vegetation.

Chloroflexa  - Green nonsulfur phototrophs

Chloroflexus  thin filamentous photosynthetic bacteria - heat tolerant found in hot springs  40-70 C

Chlorobia - Anoxiygenic green sulfur bacteria

Chlorobium tolerant of very high and low temperatures or salinities, very intolerant of oxygen (use H2S as an electron donor)

Aphragmabacteria - mycoplasmas wall less eubacteria

Mycoplasma pnumoniae  causes a type of pneumonia

Endospora - Endospore forming gram-positive bacteria

Bacillus anthracis - anthrax

Lactobacillus - lactic acid producing bacteria (found in milk)

Pirellulae - Protinaceous walled bacteria obligate intracellular parasites

Chlamydia  - species responsible for a parrot transmitted disease in humans and with a trachoma type of blindness

Actinobacteria - gram positive bacteria

Streptomyces - anti-biotic producing species .

Deinococci -Radiation or heat resistant bacteria

Thermus aquaticus   discover in hot springs in Yellowstone is the source of Taq polymerase. This DNA polymerase is the basis for PCR (Polymerase chain reaction) which is used to amplify DNA

Deinococcus can withstand a doses of up to 3,000,000 rads (500 is enough to kill a human most bacteria can be killed with 100 rads)

Thermotogae - thermophilic fermenters

A newly discover group of eubacteria in their own phylum. They are found to inhabit the hot vents at the see bottom they live at temperatures between 50 and 100C and grow optimally at 80 C