Chapter 17:The History of Life

17-1 The Fossil Record

What is a fossil?

Paleontologist: scientist who studies fossils

Fossil record: provides info about the past…

Incomplete!

How do fossils form?

Some trace of an organism must be preserved

Sedimentary rock

Several ways:Imprint of soft parts

Replace bone/wood/shell with minerals

“perfect preservation”

**not all living things leave fossils!**

Interpreting Fossil Evidence

Must find them first- earth erodes

Use pieces- rarely see whole organisms

Look for similarities/differences between fossils and current organisms

Date the fossil

Dating Fossils

1. relative dating- vertical order (oldest at bottom)

Index fossil: distinct fossil used to compare relative ages of fossils

2. radioactive dating- uses half life of radioactive element to determine age

Half life: length of time required for ½ radioactive atoms to decay

Ex: carbon- 14 (decays) and carbon 12 (no decay)

Geologic Time Scale

Represents evolutionary time

Worldwide studies

Use relative dating to organize

Use radioactive dating to get specific date

17-2 Earth’s Early History

How did life begin? (loaded question)

Current scientific view:

Young earth struck by an object (another planet?)

Heat melted the earth- all elements rearranged

Settled by density (core, crust, atmosphere)

Water!

3.8 billion years ago: Earth cooled enough for water

Oceans formed- red from iron

Life began in the water!

How did life form?

Miller and Urey

Simulated earth’s early conditions in a lab:“Primordial soup”

Hydrogen, methane, ammonia gases

Closed off experiment to any “life”

Electric spark (to simulate lightning)

Organic compounds formed! (amino acids)

Simple compounds of primitive earth can create organic compounds

Free Oxygen and Life on Earth

bacteria-like organisms were first

Increase in photosynthetic bacteria:O2 in water = ocean turns blue/green

O2 in air = sky turns blue

O2 kills many life forms

Others learn to adapt or live anaerobically

Origin of Eukaryotic Cells

Endosymbiotic theory: idea that eukaryotic organisms formed from a symbiosis among different prokaryotic organisms

Prokaryotes taken up by other prokaryotesLearn to use O2= mitochondria

Photosynthetic= chloroplast

Increasing Diversity Among Organisms

Sexual reproduction: adds genetic variation thru gene shuffling

Multicellularity

Geologic Time Line Project

Work in groups of 3

You will be assigned a time period

You will have 20 min to find the following BASIC info on your period and design a mini poster for it

Period Name

Era in which it belongs

3-5 defining characteristics

A visual- make it look nice!

Be sure to include your names

17-3 Evolution of Multicellular Life

Precambrian Time (88% of life on earth so far)

Anaerobic to aerobic organisms

Eukaryotes formed

Multicellular organisms

Life in sea only

Paleozoic Era

Characterized by diversity of marine life

Cambrian Period:“explosion” of invertebrate diversity

trilobites (arthropods)

Ordovician and Silurian Periods

Some movement to land

First vertebrate- jawless fish

Paleozoic Era (cont.)

Devonian PeriodAge of the Fishes (sharks)

First vertebrates on land (amphibians)

Carboniferous and Permian PeriodsReptiles evolve from amphibians

Mass extinction: occurs when many organisms die out at the same time

Mesozoic Era

Characterized by dinosaurs and flowering plants

Triassic PeriodAge of the reptiles

Dinosaurs

First mammals (small shrews)

Jurassic PeriodWhen dinosaurs ruled the earth…

First bird- Archaeopteryx

Mesozoic Era (cont.)

Cretaceous PeriodT-Rex ruled

Flying reptiles and birds

Shrubs and flowering plants (fruits)

Mass extinction occurs - no more dinosaurs

Cenozoic Era

Characterized as the age of the mammals

No more competition with dinosaurs

Adapted to land, sea and sky

Tertiary Period:Insects, grazing animals (grass)

Quaternary Period:

Ice ages, mammoths

Early humans -> Homo sapiens

17-4 Patterns of Evolution

Macroevolution: large scale patterns of processes that happen over a long period of time

Patterns/Trends:1. extinction

2. adaptive radiation

3. convergent evolution

4. coevolution

5. punctuated equilibrium

6. developmental genes and body plans

1. Extinction

Remember Darwin? Fighting for resources?

Other causes include loss of an entire ecosystem (mass extinctions)

Benefits: opens up habitats for survivorsUsually see a burst of evolution/diversity

2. Adaptive Radiation

Process where a single species or a small group of a species evolves into several different forms that live in different ways

Increases diversity of organisms

Ex: Darwin’s finches!

3. Convergent Evolution

Process by which unrelated organisms independently evolve similarities when adapting to similar environments

Ex: penguin (bird), shark (fish) and dolphin (mammal) all develop streamline bodies and swimming appendages

Analogous structures: structures that look and function the same but have no common evolutionary history

4. Coevolution

Process by which two species evolve in response to changes in each other

Ex: orchid’s spur hold nectar 40 cm down and a hawk moth has a 40 cm long feeding tube

5. Punctuated Equilibrium*

Pattern of evolution in which long, stabile periods are interrupted by brief periods of more rapid change

Darwin said gradualism (slow and steady)

Rapid evolution may be due to:Genetic drift- small pop.

Founder effect- small pop.

Mass extinction- opens new habitats

6. Developmental Genes and Body PlansRemember hox genes?

Genes cause changes in physical body plan- natural selection then acts on these changes

Ex: ancient insects= wings on all body segments and modern insects have wings on only 1 or 2 segments