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What is a Fossil?
What is a Fossil?
Fossils are the remains of organisms chemically changed into rock
They allow us to assess phylogeny- or evolutionary relationships
How does an animal become a fossil?
Taphonomy- the study of what happens to an organism’s remains after death
Bones will not fossilize if they are left exposed. Scavengers and weather will destroy or carry them off
Fossilization requires an oxygen-free (anoxic) environment, where decomposition is limited
Ground water and acidic soil can also erode away bone
Very few animal bones actually fossilize

Provenience of fossils is very important
To know anything about them we must know where they cam from

Types of fossils
Types of fossils
Fossils are found in different types of rock: Sedimentary and Volcanic
Sedimentary rock is made by sediment (water, rock and soil) being laid down in layers over time
This creates distinct strata, or layers
Example: South African cave site   
Volcanic ash can also bury and preserve fossils
Example: Laetoli footprints
Sometimes vestiges of DNA can be found within fossils
Chemical segments of bone can also be analyzed

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   Fossils
   Fossils
Limitations of the Fossil Record: Representation Is Important
The fossil records present a “snapshot” of life in the past
Recognition of this limitation is critical in interpreting the fossil record
The Fayum in Egypt has a rich record of early primate evolution ending at about 31 mya; later fossilization conditions may not have been as ideal as in previous millennia
The same is true of the human fossil record: the best preservation is in eastern and southern parts of Africa after 4 mya

The pace of evolutionary change:
The pace of evolutionary change:
Phyletic Gradualism- slow accumulation of changes over time
Punctuated Equilibrium- Sudden, stochastic speciation events. Members of the isolated species outcompetes and replaces the the ancestral species

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Just How Old is the Past?
Just How Old is the Past?
Time in perspective
To understand fossils and evolution we must understand deep time
Geologic time: Earth History
Geology has established three eras of time in Earth’s history
Paleozoic
Mesozoic
Cenozoic
Changes to the Earth’s continent Pangaea and oceans occurred as mammalian, primate and human evolution was occurring

The Earth is 4.5 billion years old
The Earth is 4.5 billion years old
600 million years ago (mya)- First diversification of life forms occurred
410 mya- Evidence of first land animals
225 mya- Dinosaurs and early mammals
65 mya- Dinosaurs go extinct; Adaptive radiation of mammals and birds
Changes to the Earth’s continent Pangaea and oceans occurred as mammalian, primate and human evolution was occurring

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How old are these things anyway?
How old are these things anyway?
Two main dating methods: Relative and Absolute (Numerical)
Relative Methods of Dating: Which Is Older, Younger, the Same?
Those at the bottom of a stratum are older than those nearer the top (Law of Superposition)
Stratigraphic Correlation
Matches up strata based on the scale of time in a large region
Chemical Dating
Fluorine dating measures levels of fluorine in bones to determine relative age

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How old are these things anyway?
How old are these things anyway?
Two main dating methods: Relative and Absolute (Numerical)
Biostratigraphic (Faunal) Dating
Faunal dating compares different fossil forms based on the first appearance of an organism through its extinction
Cultural Dating
Cultural dating uses changes in material culture (such as stone tools) to establish a chronology.

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How old are these things anyway?
How old are these things anyway?
Absolute Methods of Dating: What Is the Numerical Age?
Absolute (numerical) age results in a numerical time scale
Dendrochronology counts the rings of trees; each ring marks one year of growth
The Radiometric Revolution and the Dating Clock
Radiocarbon dating measures the half-life of carbon isotopes.
This method is most accurate for only the last 50,000– 70,000 yBP.
Radiopotassium Dating
Radiopotassium dating measures the potassium radioisotope in volcanic rock associated with fossils
Potassium has a long half-life, and can be used to date fossils older than 200,000 years

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How old are these things anyway?
How old are these things anyway?
Genetic Dating: The Molecular Clock
Amino acid dating, based on the decay of protein molecules, is useful for fossils up to 200,000 years old and, in some settings, 1mya
Fission track dating is based on changes in uranium-238 and is used to date volcanic ash and glass millions of years old
Paleomagnetic dating uses changes in the earth’s magnetic field to date rock

How old are these things anyway?
How old are these things anyway?
Genetic Dating: The Molecular Clock
Electron spin resonance dating takes a measure of radioisotope buildup in fossils over time.
Luminescence dating takes the amount of the sun’s energy in sediment, stone, or ceramic.
The molecular clock measures changes in DNA over time and is used to examine the timing of the splits in primate and human evolution

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Reconstruction of Ancient Environments and Landscapes
Reconstruction of Ancient Environments and Landscapes
In addition to constructing time scales, researchers also try to reconstruct ancient environments.
The driving force in shaping environment: Temperature
Temperature drives climate, which is linked to biology and chemistry
Ancient temperatures are reconstructed through study of ocean dwelling organisms
One of the most dramatic changes in temperature occurred around 6 mya and was a cooling period in Earth’s history

Reconstruction of Ancient Environments and Landscapes
Reconstruction of Ancient Environments and Landscapes
Chemistry of animal remains and ancient soils: Windows onto diets and habitats
Chemical analysis of bones and teeth can reconstruct diets and habitats based on plants the animals ate
Different environments are associated with different types of carbon dioxide (e.g., C3 or C4)
Time, space, habitat, and diet are important factors in the interpretation of the fossil record

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