Plant diversity means there are many different kinds of plants. 

Question: How did all this diversity arise?

Hypothesis 1: All life (both simple and complex) was created at one time.

Hypothesis 2: Life started out simple and developed complexity over many years.

Experiment:

Evidence of life is found in the fossil record. For example, the Grand Canyon is made of sedimentary rock with lower layers older and higher layers younger. Therefore, fossils deposited in the layers of the canyon provide a record of life’s history. 

Prediction 1:

If H1 is true, then simple and complex life forms should be found equally throughout different canyon layers

Prediction 2:

If H2 is true, then simple forms should be found in older (lower) layers, and both simple and complex should be found in younger (higher) layers.

Results:

• Fossils in the Grand Canyon conform to prediction 2. 
• Organisms in adjacent layers resemble one another more closely than organisms in widely separated layers (e.g. the top vs. bottom layer is very different). 
• Today's living organisms are most similar to fossils in the _________________layer.

Conclusion:

Reject H1

Accept H2

 "The crust of our earth is a great cemetery where the rocks are the tombstones on which the buried dead have written their own epitaphs."

                                                                                                                        Louis Agassiz, scientist 1807-1873

For another example of life's history in the fossil record, read about the John Day fossil beds of Oregon at  www.nps.gov/joda/

Evolution

1. Charles Darwin sailed at age 22 on HMS Beagle for 5 years p.135

Darwin noted diversity in:

• Fossil species
• Living species
• Species on different continents

c. 1859 Published "The Origin of the Species"

2. Diversity arises by natural selection or "survival of the fittest" p.136

variation: differences exist within organisms

overproduction: populations in nature produce more individuals than can survive

competition: individuals compete for limited resources (eg, space, light,water)

survival to reproduce: those individuals better suited to the environment survive and reproduce

3. Evolution

Over time, populations of organisms change (evolve) in response to changes in the environment.  Darwin called this "descent with modification".

4. Adaptations are traits that allow individuals to survive in a particular environment

Examples of adaptions:

• cactus spines
• hummingbird beak
• antibiotic resistance in bacteria

How does grass grown in heavy metal soils near old mines in England? p. 136

Most grass will not grow on soil high in copper,zinc,nickel. Yet, mine tailing in Wales are covered with grass. How is this possible?

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NOTE WELL:

Individual grass plants did NOT become altered because of the metal.

Most grass plants died and only those able to tolerate the metal survived to reproduce. 

5. Evidence of evolution in living plants

Vestigial  structures:  Leftover structures.  Structures are present that have no function or not the normal function.

Examples:

• Air plants with roots that don’t absorb water
• Water plants with stems that don’t transport water

Homologous structures: Many structures are similar between many different plants which demonstrates common ancestry. All barrel cactus share a common ancestor which gave rise to many lines of descent.  We say they arose by divergent evolution. 

Examples:

• Barrel cactus exist, from giant Saguaros to tiny mammalaria, have succulent stems and spines.
• All flowering plants share a common ancestor that arose about 125 million years ago. Flowers range in size, color, and shape.  Yet, they share many common features.