EESA06H3 Lecture Notes - Lecture 6: Cambrian Explosion, Paleozoic

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22 Apr 2012

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Step 1: A Very Short History of Life on Earth:
Various steps of evolution of life on earth.
First one: The earliest Bacteria: 3.8 Ga
Age of Earth: 4.56
The earliest bacteria was not here at the beginning of earth..
^ why not?? earth had lots of magma when it was formed.. so bacteria took a while to form
Life evolved around MORs
Bacteria could live in hot areas- magma
How are fossils formed?
- First one in slide 26 : nice shell, next one is a fossilized tree trunk: petrified wood, & idea
of having to dig through rocks & sediments.
- They are formed with the process of mineralization
- For example: a snail that dies, the soft parts are eaten by bacteria, but you are left with
the shell & overtime sediments bury the shell & it adds pressure on the snail shell the
sediments near to the bottom of the pile LITHIFY (turn into rock) & the little snail shell is
affected by hot water that comes through the rock.
- Water underground has stuff inside of it: silica, iron
- Overtime the minerals replace the shell a nice model of what the creature shell
- It is difficult to keep a soft body
- ^ Per mineralization
- One of the first philosophers talked about the age of the earth was actually looking at
fossils of creatures that were living in water but their bodies were on top of the great
- How can we see fossils??
Those rocks were uplifted by tectonic forces
- Ammonite: an organic gemstone..fancy mineral name: aragnite
- It’s coloured by the chemical editions: Iron, Aluminum
- All minerals are usually colored
- Some fossils are like footprints in the sand & sometimes they get preserved: trace
fossils (show evidence)
- Study of trace fossils: ichnology
- Trace fossils; creatures doing stuff to the sediments; changing the sediment; burrowing
- Sedimentary geologist: sometimes the creatures destroy the upper sediments so
geologists have to be careful
- Sediments: common in carbonate or limestone rocks in Ontario; comes from the SEA
LILY: made of a long stem & mop head… they live in shallow water & storms break up
the bodies.. you usually find the broken up parts not the whole stem
- the fossils tell us about the environments & they tell us what kind of creatures live there
- Pale ecologists: study of ancient organisms & environments.
- Crinoid: fancy name for sea lily
- Fossil morphology: the way your body looks; hot climate-tall, cold climate-shorter
- Stratigraphy: studying layers of rock
- Fossils help us give us a relative age of rocks
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- Geologic range: The span of time (NOT SPACE) in which something lives ;creatures come
& go
- Large geographic range but small geologic range is a GREAT FOSSIL (found in many
places but didn`t exist for long)
- William Smith: canal engineer; one of the first to figure out that fossils came from
different time
- The geologic time scale: the parts in blue ; it was created using fossils
- Relative age: I`m older than you (but you don’t know the age)
- Chart: geologic range: dots connected with lines slide 32
- Index fossils
- Trilobite fossils; molted like a snake
- The pre Cambrian is truncated; squished into a small section
Prokaryotes: some are photosynthetic; blue green algae (they don’t have a nucleus)..
microscopic & only have ONE CELL
- Earliest: Archaea- probably lived at MORs lots of warmth
- 3.8-2.0 years ago- only things existing
- Know Eukaryotes!!!!
- Hydrothermal vents- smokers
- Hypothermal fites: live in really hot water.. greater than 100 degrees C.. no light down
there.. get there light from Kemosynthesis
- Th
- Oldest cyanobacteria- 3.5 million years ago found in AUSTRALIA
- Dubious
- Stromatolites; greek for stoney carpet
- They are on mounts- hills, layer of sticky bacteria & fine muds come & stick onto the
- Cynobacteria; lots of iron around but it wasn’t rusted bcuz there wasn’t oxygen
- Eventually the iron on earth began to rust; banded iron formation (BIF)
- We get 90% of iron from here- steel
- Iron was coming out of the MORs- mafic rocks (iron, mg)
- Developed 2.8 years ago
- Protists
- Reproduce sexually; allowed mutations
- the first multicellular; metazoans
- Ediacara- multicellular
- NFLD- from Newfoundland
Step 2: Cambrian Explosion: 540 Million years old
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