Descriptive notes explaining the fossil record, lagerstatten, evolutionary trends, evolution of vertebrates, mass extinctions, global climate, evidence for past climates, the influence of greenhouse gases, tectonics and volcanoes on the environment, and the Anthropocene.
Past Life and Past Climate
Fossil Record
Fossils are the most direct evidence for past life. They have may purposes:
• To determine the relative age of rock
• To determine the palaeoenvironment conditions at the time of deposition
• To study the process of evolution
Classification of Organisms
E.g. Humans can be classified as:
King Kingdom Animalia
Philip Phylum Chordata
Came Class Mammalia
Swiftly Subclass
Over Order Primates
For Family
Good Genus Homo
Soup Species Sapiens
Exceptionally Preserved Fossils
Lagerstätten – fossiliferous deposits that are rich in palaeontological information
• They are exceptionally well preserved, showing exceptional detail including soft parts and feathers
• They provide a more complete ‘snap-shot’ of the community
• 2 types – conservation and concentration
Conservation Trap
Organisms (insects, birds, feathers) become trapped and fossilised/preserved
Resin in tree sap/amber
3D, could show local ecosystem
Hyper saline
Stagnation Anoxic conditions in stagnant water means no predators so organisms aren’t
broken up and get covered rapidly
Organisms in deep marine get swamped and suffocated by sediment e.g.
turbidity current
Obrution (Rapid Burial)
Soft parts preserved in flat fossils
e.g. Burgess Shales
Concentration Deposits
Vast numbers of fossils but not necessarily the best preservation
Concentration Deposits
Usually shows growth series
Why are they important for the geological record?
• Exceptionally well preserved, showing exceptional detail including soft parts and feathers
• Provide a more complete view of the fossil record
Examples of Lagerstätten
Burgess Shale, British Colombia, Rhynie Chert, Solnhöfen Limestone, Bavaria,
Canada Scotland Germany
Age Cambrian 400Ma Jurassic
Organisms Opabinia, Wiwaxia, Aglophyton Plants include seed ferns,
Preserved Anomalocaris, Pikia, Marella, conifers adapted to dry
Annelid Worms, etc. conditions
, Archaeopteryx – link between
dinosaurs and birds
How Were 509Ma – marine avalanche Organisms coated in Hypersaline – dry conditions so
They causing rapid covering. Slowed silica rich water, evaporation. Lagoon conditions
Preserved? decaying and stopped scavenging stopping decay - Stagnation
– Obrution
Significance Unique fossils – not seen in later First land based Produced fossils of exceptional
of Deposit aged rocks plant. Allowed quality, including soft bodied
Cambrian explosion animals to on land – material. Terrestrial & marine
Whole ecosystem preserved life source preservation
Best preserved
terrestrial fauna
Evolutionary Trends
Evolution – the progressive development of new life forms
There are two interpretations for evolutionary patterns based upon the fossil record:
• Gradual Evolution
- Implies slow genetic change as one species replaces another by the process of natural selection
- Proposed by Charles Darwin and Russell Wallace
- Gradualism is uncommon as it can’t account for the huge number of species that have evolved
with the geological timescale or explain the organisms which suddenly appear
• Punctuated Equilibrium
- Implies long periods of stability (stasis) where the characteristics of animals stay the same for a
long time followed by rapid change (radiation) in the characteristics
- Likely to be a response to climatic/environmental/ecological changes or mass extinctions
Missing Link – A missing intermediate species from the fossil record
Evolution of Life on Earth
46,000Ma
Start of Earth
4.6Ga
3.8 billion years ago
Single celled organisms (cyanobacteria) started to photosynthesise
Bacteria
3.4 billion years ago Cyanobacteria in stromatolite traps, bind and cement sedimentary grains together
Stromatolites onto microbial biofilm
The oscillation between oxidised and reduced iron layers hint at seasonal bloom of
2.4 billion years ago
cyanobacteria.
Banded Iron
Cyanobacteria produce oxygen and oxidise the iron dissolved in sea water allowing
Formation (BIF)
it to precipitate on the sea floor
Rapid diversification afterwards
700 million years ago 70% of life became extinct
Snowball Earth Warm equatorial waters couldn’t get to south pole so got colder – whole planet
covered in ice
Mistaken Point fauna first
640 million years ago
Flinders Range fauna – bilateral symmetry, organisms can move to find food,
Ediacara
sensory organs in the head. Evidence of sexual reproduction
545Ma
Start of Phanerozoic Era
Cambrian Explosion
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