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Evolution of phenotype . Evolution of diversity . Evolution in the Fossil Record. The Earth is Old. The Geological Time Scale is Based Upon the Principles of Relative Dating. Younger rocks are deposited on top of older rocks Lava and sedimentary rocks were originally laid
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Evolution of phenotype Evolution of diversity Evolution in the Fossil Record
The Geological Time Scale is Based Upon the Principles of Relative Dating • Younger rocks are deposited on top of older rocks • Lava and sedimentary rocks were originally laid • down in a horizontal position • Boulders or cobbles found in a body of rock are • older than their host rock • Earlier fossil forms are simpler than more recent • forms, and more recent forms are most similar to • existing forms.
Geologic Column Earth’s history as told by rock strata
The Geologic Time Scale Chapter 4, p. 70
Why is the fossil record incomplete? It takes the right conditions at the right time in the right place. - some organisms are simply not likely to yield fossils - sedimentation does not occur in all habitats - fossils must survive geological events and weather the elements for millions of years before discovery
Process of Fossilization After remains are buried by sediments: Compression/impression/casts/molds:impressions or casts made before decomposition (like footprints). (2) Permineralized fossils: precipitation of minerals in cells before decomposition. Or Occasionally: (1) Unaltered remains: Frozen, amber embedded, peat bogs.
permineralized fossils amber cast Impression fossil
Fossil Record is Biased Fossilization is higher for organisms that are: Durable and likely to be buried in an anoxic environment (low land or marine habitats) Also, there is temporal and geographic bias: Probability that an organism will be fossilized depends on the geographical area and historical time.
Daughter Atom Parent Atom Radiometric Dating Fossils and associated rocks contain reactive elements that decay at known rates • Uranium235 --> Lead235 = 7 x 108 years • Carbon14 --> Nitrogen14 = 5730 years Half-life
Accumulating Daughter Atoms 1/1 Surviving Parent Atoms 1/3 1/7 2 3 1 Time (half-lives) Radioisotope Decay 1. Find fossil 2. Determine ratio of parent to daughter atoms 3. Determine number of elapsed half-lives 4. Estimate age of fossil
You are using C14 (half-life = 5730 years) radioisotope dating to determine the age of rocks associated with a fossil. The percentage of daughter isotope atoms (N14)) is 87.5%. What is the age of the fossil? Try this problem 17,190 yrs
There are Good Examples of Macroevolution in the Fossil Record Sarcopterygii --> Ichthyostega --> Amphibia • see also (Figure 4.6) Gradualism : (e.g. limbs are intermediate) Mosaic evolution: (limbs evolved faster than braincase, tail fin, tooth structure
4.6(1) Eusthenopteron, a member of the group of lobe-finned fishes from which tetrapods arose
4.6(2) Eusthenopteron, a member of the group of lobe-finned fishes from which tetrapods arose
Other Examples From Book To Review(Chapter 4) • Origin of Birds • Archaeopteryx is but one of many fossils • Origin of Mammals - Gradual evolution of “reptilian” skull and jaw • Origin of Cetacea • A series of fossils have recently been discovered showing adaptation to aquatic life • Origin of Hominins • We are the lone survivors of an otherwise extinct radiation of bipedal African hominids