1. Chapter 14
The History of Life

2. Section 14.1: Fossil Evidence of Change
Fossils provide evidence of the change in organisms over time.
Earth’s early history
Land environments
Earth formed about 4.6 billion years ago
Volcanic features
Atmosphere
Volcanic gases: H2O; CO2; SO2; CO; H2S; HCN; N2; H2

3. Section 14.1: Fossil Evidence of Change
Atmosphere (cont.)
Earth’s early atmosphere had little or no free oxygen
Clues in Rocks
Earliest date of life on Earth: 3.5 billion years ago
The fossil record
A fossil is any preserved evidence of an organism

4. Clues in Rocks Table 14.1 on page 393: Categories of Fossil Types
Trace fossil
Molds and casts
Replacement
Petrified or permineralized
Amber
Original material

5. Fossil formation Fossils do not form in igneous or metamorphic rocks
Nearly all fossils are formed in sedimentary rock
Figure 14.2
Organisms usually become fossilized after they die and are buried by sediment
Sediments build up in layers eventually encasing the remains in sedimentary rock
Minerals replace or fill in the pore space of the bones and hard parts of the organism
Erosion can expose the fossils

6. Fossil formation A paleontologist – a scientist who studies fossils
Dating fossils
Relative dating – method used to determine the age of rocks by comparing them with those in other layers
Based on the law of superposition (Figure 14.3 pg.395)
Younger layers on top of older layers

7. Dating Fossils
Radiometric dating – uses decay of radioactive isotopes to measure the age of a rock
Requires the half-life of the isotope (amount of time it takes for half of the original isotope to decay)
Uranium 238 Lead 206 (half-life of 4510 million years)
Radioactive isotopes are found only in igneous or metamorphic rocks

8. Dating Fossils Carbon-14 used to date mummies, bones and tissues
The Geologic Time Scale
Page 397
A model that helps in comprehending biological events
Eras and periods are defined by geological events; particular layers in rocks or when chemicals (oxygen) became present

9. Geologic Time Scale
Epoch – smallest unit lasting several million years
Period –tens of millions of years
Era – consists of two or more periods lasting hundreds of millions of years

10. Precambrian The first 4 billion years 90 percent of Earth’s history
Earth formed
Life appeared – autotrophic prokaryotes
Eukaryotic cells emerged
Life was flourishing; first animals appeared
Extensive glaciation marks second half of this period
Short food chains
Marine ecosystems

11. The Paleozoic Era Drastic change in animal life
Cambrian explosion – major animal groups diversified
Changes in ocean life
First life on land – led to reptiles
Mass extinction – many species become extinct in a short time
Occurred every 26 to 30 million years on average
60 – 75 percent of species alive became extinct
90 percent of marine organisms disappeared during Permian extinction

12. Extinction Due to geological forces Volcanic activity
Disrupted ecosystems
Changed the climate

13. The Mesozoic Era Early mammals dominant land animals
Mammals and dinosaurs
Flowering plants evolved from non-flowering plants
Birds evolved from predatory dinosaurs
Reptiles (dinosaurs) dominant organisms on the planet
Then 65 million years ago, a meteorite struck Earth!

14. The Mesozoic Era
K-T boundary : layers of rock providing evidence of meteorite impact
Found iridium, rare to Earth, common to meteorites
Led to mass extinction of dinosaurs and many plant species
Affected global climate
Those that could not adjust to changing climate disappeared

15. The Mesozoic Era
Continental drift – theory behind plate techtonics

16. The Cenozoic Era Most recent Mammals became dominant land animals
Most were small (shrews)
Humans have been around a relatively short time on Earth