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Chapter 2: Written In the Rocks
Making the Record
Process: reach bottom of water; get covered by sediments (thus, rare fossils of dead plants
and land animals); soft parts aren`t preserved causing a bias (explains lack of worms and
jellyfish fossils); many are too buried in the earthโ€™s surface to reach and many lost to
natural forces like weather. Thus, fossil records severely incomplete.
Relative age ๎€ Layers dictate age, but not all layers laid down in one place. Must therefore
cross-reference. (Same type of rock with same type of fossil= same age)
Actual age๎€radioactivity. Different isotopes decay at different rates. (Radiometric dating)
The Facts: Evidence of Evolution in Fossils
1)Early life simpler than complex modern life
2)Visible connected changes in lineage; most modern fossils have similar traits to
living organisms
3)Transitional species in fossils (Darwin did not have this) ๎€transition ancestor differs
in some respect to all descendants (not an intermediate mix of the two)๎€i.e. birds
and reptilesโ€”reptiles older so ancestor must have looked like a reptile- wings and
other bird traits evolve so much later on in the lineage ๎€fossils need not be one
single species but rather fossils that show linking traits (dating most important)
4)Bacteria๎€Simple eukaryotes๎€ multicellular organisms (worms, jellyfish,
sponges)๎€terrestrial plants and tetrapods๎€amphibians๎€reptiles๎€mammals and
5) Mosses and algae๎€ferns๎€conifers๎€deciduous trees๎€flowering plants
6)Pace of evolution need not be even๎€due to fluctuating environment (strength of
natural selection varies)
7)Not all species must evolve
8)On to Land: Fish to Amphibiansโ€”Shubinโ€”Canadian Artic: Ellesmere Island:
TIKTAALIK๎€direct link to lobe-finned fish and amphibians: had gills, scales, fins,
flat head like salamander, eyes and nostrils on top of head and not on the sides,
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