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Published on 3 Mar 2011
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 earths 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 ageradioactivity. 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 reptiles—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)BacteriaSimple eukaryotes multicellular organisms (worms, jellyfish,
sponges)terrestrial plants and tetrapodsamphibiansreptilesmammals and
5) Mosses and algaefernsconifersdeciduous treesflowering plants
6)Pace of evolution need not be evendue to fluctuating environment (strength of
natural selection varies)
7)Not all species must evolve
8)On to Land: Fish to Amphibians—ShubinCanadian Artic: Ellesmere Island:
TIKTAALIKdirect 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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