1. The History of Life
Unit V
Chapter 17

2. Fossils and Ancient Life
A fossil is the preserved remains or evidence of an ancient organism
Scientists who study fossils are paleontologists
The fossil record is the grouping of similar organisms from oldest to most recent
It can provide evidence about the history of life on Earth and show how different groups of organisms have changed over time

3. Extant v/s Extinct
More than 99 percent of all species that have ever lived on Earth have become extinct
The term extinct is used to describe a species that no longer has a living representative
The term extant is used to describe a species that has living representatives

4. The Formation of Fossils
A fossil can be as large and complete as an entire, perfectly preserved animal, or as small as a tiny fragment of a jawbone or leaf
For a fossil to form, either the remains of the organism or some trace of its presence must be preserved
The formation of any fossil depends on a precise combination of conditions
Because of this, the fossil record provides an incomplete record of the history of life – for every organism that leaves a fossil, many more die without leaving a trace

5. The Formation of Fossils
Figure 17-2 Formation of a Fossil
The Formation of Fossils
Section 17-1
Water carries small rock particles to lakes and seas.
Dead organisms are buried by layers of sediment, which forms new rock.
The preserved remains may later be discovered and studied.
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6. Radioactive Dating
Radioactive dating is the use of half-lives to determine the age of a sample
Radioactive elements decay, or break down, into non-radioactive elements at a steady rate called a half-life
A half life is the length of time required for half of the radioactive atoms in a sample to decay
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

7. Formation of Earth
Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water
About 4 billion years ago, Earth cooled enough to allow the first solid rocks to form on its surface
About 3.8 billion years ago, Earth’s surface cooled enough to allow water to remain liquid
Could organic molecules evolve under these conditions?

8. The First Organic Molecules
Section 17-2
Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive earth.
Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water.
Spark simulating lightning storms
Mixture of gases simulating atmospheres of early Earth
Cold water cools chamber, causing droplets to form
Condensation chamber
Water vapor
Liquid containing amino acids and other organic compounds
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9. Origin of Eukaryotic Cells
The endosymbiotic theory, championed by Lynn Margulis, proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms
Chloroplast
Plants and plantlike protists
Aerobic bacteria
Ancient Prokaryotes
Photosynthetic bacteria
Nuclear envelope evolving
Mitochondrion
Primitive Photosynthetic Eukaryote
Animals, fungi, and non-plantlike protists
Ancient Anaerobic Prokaryote
Primitive Aerobic Eukaryote
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10. Patterns of Evolution
Macroevolution refers to the large scale evolutionary changes that take place over long periods of time
Six important patterns of macroevolution are:
Mass extinctions
Adaptive ratiation
Convergent evolution
Coevolution
Punctuated equilibrium
Changes in developmental genes

11. Mass Extinctions Extinctions occur all the time
More than 99% of all species that ever lived are extinct today
Usually, extinctions occur at a constant rate
Several times, however, huge numbers of species have disappeared in mass extinctions
Paleontologists think that most mass extinctions in the past were caused by multiple factors
Asteroids
Volcanic activity
Changing position of continents
Changing sea levels

12. Adaptive Radiation
The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges is called adaptive radiation.
Adaptive radiation typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors.
Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the mass extinctions of dinosaurs 65 mya.

13. Convergent Evolution
Convergent evolution describes 2 unrelated species that share similar traits.
These similarities are not due to common ancestry, but rather a result of similar environmental factors.

14. Coevolution
Coevolution describes the evolution of one species in response to new adaptations that appear in another species of which the first shares close interaction

15. Punctuated Equilibrium
Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
Typically occurs when new niches become available following a mass extinction

16. Developmental Genes & Body Plans
Hox Genes are a stretch of DNA sequence found in genes involved in the regulation of the development (morphogenesis) of animals, fungi and plants
Correlations between Hox genes and major evolutionary events are apparent…major changes between animal phyla are correlated with duplications in Hox genes or an increase in the number of Hox genes

17. Speciation Flow Chart Section 17-4 Species Go to Section: that are
Unrelated
Related
form in
under
under in in
Inter-relationshiops
Similar environments
Intense environmental pressure
Small populations
Different environments
can undergo
can undergo
can undergo
can undergo
can undergo
Coevolution
Convergent evolution
Extinction
Punctuated equilibrium
Adaptive radiation
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