1. Chapter 17 – Miller · Levine
The History of Life
Chapter 17 – Miller · Levine

2. Fossils Paleontologists – scientists who study fossils
Infer what past life forms were like
Classify fossil organisms
Fossil record – information about past life
Provides evidence about the history of life on Earth
Shows how different groups of organisms have changed over time

3. How Fossils Form
Either the remains of the organism or some trace of its presence must be preserved
Most fossils form in sedimentary rock
An imprint of soft parts can be made
The hard parts can become mineralized
Can be preserved in rock, ice, amber, tar, etc.

4. Relative Dating
The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock
Older fossils will be in the bottom layers
More recent fossils will be in the upper layers
Index fossils – fossils of species that existed for a short period but had a wide range
Allows paleontologists to estimate a fossil’s age compared with that of other fossils

5. Relative Dating

6. Radioactive Dating
Scientists use radioactive decay to assign absolute ages to rocks
Calculate the age of a sample based on the amount of remaining radioactive isotopes it contains
Half-life – the length of time required for half of the radioactive atoms in a sample to decay

7. Geologic Time Scale
Precambrian Time – covers about 88% of Earth’s history
Paleozoic Era – many vertebrates and invertebrates
Mesozoic Era – “Age of the Dinosaurs”
Mammals evolved
Cenozoic Era – “Age of Mammals”
Eras are subdivided into periods

8. Geologic Time Scale

9. Formation of Earth
Pieces of cosmic debris were probably attracted to one another
The early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water
Violent volcanic activity, comets and asteroids bombarded the surface, oceans did not exist
About 3.8 billion years ago, Earth’s surface cooled enough for oceans to form

10. How Did Life Begin?
The first organic molecules were able to form because of the atmosphere being bombarded by electricity (lightning)
RNA probably evolved before DNA

11. The Rise of Oxygen…
The first life forms must have evolved in the absence of oxygen (anaerobic prokaryotes)
Over time, photosynthetic bacteria evolved, adding oxygen to the atmosphere
The ozone layer formed
The rise of oxygen caused some life forms to go extinct while other organisms evolved

12. Endosymbiotic Theory
Prokaryotic organisms entered the “ancestral eukaryote”
Formed a symbiotic relationship
Some had the ability to perform respiration – became modern mitochondria
Others could perform photosynthesis – became the modern chloroplasts

13. Endosymbiotic Theory

14. Macroevolution
Large scale evolutionary changes that take place over long periods of time
Mass extinctions
Adaptive radiation
Convergent evolution
Coevolution
Punctuated equilibrium

15. Mass Extinctions Extinction occurs all the time
More than 99% of all species that have ever lived are now extinct
Mass extinctions occur when large numbers of species go extinct in a relatively short period of time
Most mass extinctions were probably caused by multiple factors
Usually followed by mass speciation

16. Adaptive Radiation
A single species or a small group of species has evolved into several different forms that live in different ways
Also known as divergent evolution
Often caused by geographic isolation – geological change (river, canyon, or mountain) that isolates segments of a population

17. Adaptive Radiation

18. Convergent Evolution
Adaptive radiation in groups of different organisms in different places or at different times, but in similar environments
Unrelated organisms resemble one another
Analogous structures – look and function similarly but do not share a common ancestry
Fins of dolphins, seals, penguins, sharks

19. Coevolution
Sometimes organisms that are closely connected to one another evolve together
An evolutionary change in one organism may be followed by a corresponding change in another organism
Snails developed thicker shells, so crabs evolved stronger claws
Plants produce poisonous chemicals, herbivores evolved the ability to detoxify these chemicals

20. Gradualism vs. Punctuated Equilibrium
Gradualism – biological change is a slow and steady process
Punctuated equilibrium – long, stable periods interrupted by brief periods of more rapid change