Life on Earth has changed dramatically throughout the course of geologic
history
I. Fossils and the Study of Past Life
A. What are fossils?
=> Definition: The remains or trace
of organisms preserved from the
geologic past........
*Paleontology => studies the biology,
ecology, evolution, and the time
component of fossils.........…
B. How do fossils form?
=> a very small fraction of organisms that have lived on Earth represented as fossils......Why?
Taphonomic processes - decay, scavengers, currents, waves, etc.
1. Requirements for preservation
a. hard parts => a skeleton
b. rapid burial => escape most taphonomic processes
*Some groups of organisms with poor fossil record...
=> Marine versus Terrestrial......which is better?
=> Soft Bodied versus Skeletonized
=> Bias in the fossil record
2. Types of preservation...
a. Unaltered Skeleton
- bones and teeth
b. Petrification/Permineralization
- pores filled with silica
c. replacement (pyrite and quartz)
- atom for atom replacement
d. molds and casts
- shell dissolved away
e. Carbonization
- organics in plant preserved as carbon film
- similar process to forming coal
* exceptional preservation
- most of organism preserved - including soft parts
1) freezing
2) mummification
3) amber
C. Types of Fossils
=> all Kingdoms of Life represented (some better than others)
1. Body Fossils
- skeletons
2. Chemical Fossils
- chlorophyll
3. Trace Fossils
a) tracks
b) burrows
- records the behavior of organisms
PROBLEM: not always possible to determine trace maker
Oddballs
4. Coprolites ("coprolites happen") and gastroliths
D. Importance of Fossils
1. History of Life on Earth => Evolution
2. Evidence of past environments and climates
3. Plate Tectonics
4. Biodiversity
5. Relative Time
II. Evolution -> evidence from the fossil record
A. organic evolution = inheritable change
=> observations: 1) fossil succession => changes through time
=> explanation: Evolution => living organisms have come into being as a result of the sum of changes brought about as a result of the evolutionary transformation of quite different forms of life. All living organisms are the evolutionary descendants of life forms that lived in the past..…
Descent with modification
1. Evolution => mechanisms
2 important discoveries
=> Natural Selection - Darwin’s contribution
-the individuals that are the most fit (fitness) survive to reproduce
to pass their genes along to the next generation
- Darwin didn’t understand heredity
=> Modern Synthesis Genes, DNA, and Chromosomes
- parents contribute 1/2 of genetic material to offspring
- DNA can replicate itself
- genes can be altered - source of variation
2. Mechanisms........
=> Speciation - isolated populations lead to reproductive isolation and new species
=> Adaptive Radiation - high rates of speciation to fill unoccupied ecospace
EX: Darwin’s Finches
3. The speed of evolution
a. phyletic gradualism
- after speciation, evolutionary change take place very slowly
b. punctuated equilibrium
- evolutionary change occurs very rapidly
Evolution is not linear……………….different groups sharing
Common ancestry……..descent with modification
B. History of Life
1. Evolutionary Change
=>single-celled life (~3.6 b.y.)
=>multicellular life (~1.0 b.y.)
=> "Cambrian Explosion"(543 m.y.)
=> "age of invertebrates"(543 m.y.)
=> "age of fish"(438 m.y.)
Early Fish => Placoderms & Sharks
=> "age of amphibians"(360 m.y.)
Paleozoic amphibians = salamanders with big teeth
=> "age of reptiles"(245 m.y.)
The ancestors of modern birds…...
=> "age of mammals"(66 m.y.)
The Early Cenozoic in the midwest
2. Evolution = Change: is this change progressive, directed, and predictable?
Would the evolutionary pathway experienced by life on Earth repeat itself???
3. Mass Extinction
=> the path of evolution has been affected by catastrophic events...
Mass Extinction => mechanisms
a. climate change & loss of marine shelf environments
-plate tectonics
-orbital variations
b. bolide impact
iridium
"shocked quartz"
spherules