Chapter 17:The History of Life

17-1 The Fossil RecordWhat is a fossil?Paleontologist: scientist who studies fossilsFossil record: provides info about the past…Incomplete!

How do fossils form?Some trace of an organism must be preservedSedimentary rockSeveral ways:

Imprint of soft partsReplace bone/wood/shell with minerals“perfect preservation”

**not all living things leave fossils!**

Interpreting Fossil Evidence

Must find them first- earth erodesUse pieces- rarely see whole organismsLook for similarities/differences between fossils and current organismsDate 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 decayEx: carbon- 14 (decays) and carbon 12 (no decay)

Geologic Time ScaleRepresents evolutionary timeWorldwide studiesUse relative dating to organizeUse 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 rearrangedSettled by density (core, crust, atmosphere)

Water!3.8 billion years ago: Earth cooled enough for waterOceans formed- red from ironLife began in the water!

How did life form?Miller and UreySimulated earth’s early conditions in a lab:

“Primordial soup”Hydrogen, methane, ammonia gasesClosed 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 firstIncrease in photosynthetic bacteria:

O2 in water = ocean turns blue/greenO2 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 organismsProkaryotes taken up by other prokaryotes

Learn to use O2= mitochondriaPhotosynthetic= chloroplast

Increasing Diversity Among Organisms

Sexual reproduction: adds genetic variation thru gene shufflingMulticellularity

Geologic Time Line Project

Work in groups of 3You will be assigned a time periodYou will have 20 min to find the following BASIC info on your period and design a mini poster for it

Period NameEra in which it belongs3-5 defining characteristicsA 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 organismsEukaryotes formedMulticellular organismsLife in sea only

Paleozoic EraCharacterized by diversity of marine life

Cambrian Period:“explosion” of invertebrate diversitytrilobites (arthropods)

Ordovician and Silurian PeriodsSome movement to landFirst vertebrate- jawless fish

Paleozoic Era (cont.)Devonian Period

Age of the Fishes (sharks)First vertebrates on land (amphibians)

Carboniferous and Permian PeriodsReptiles evolve from amphibiansMass extinction: occurs when many organisms die out at the same time

Mesozoic EraCharacterized by dinosaurs and flowering plants

Triassic PeriodAge of the reptilesDinosaursFirst mammals (small shrews)

Jurassic PeriodWhen dinosaurs ruled the earth…First bird- Archaeopteryx

Mesozoic Era (cont.)Cretaceous Period

T-Rex ruledFlying reptiles and birdsShrubs and flowering plants (fruits)Mass extinction occurs - no more dinosaurs

Cenozoic EraCharacterized 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, mammothsEarly humans -> Homo sapiens

17-4 Patterns of Evolution

Macroevolution: large scale patterns of processes that happen over a long period of timePatterns/Trends:

1. extinction2. adaptive radiation3. convergent evolution4. coevolution5. punctuated equilibrium6. developmental genes and body plans

1. ExtinctionRemember Darwin? Fighting for resources?Other causes include loss of an entire ecosystem (mass extinctions)Benefits: opens up habitats for survivors

Usually see a burst of evolution/diversity

2. Adaptive RadiationProcess where a single species or a small group of a species evolves into several different forms that live in different waysIncreases diversity of organismsEx: Darwin’s finches!

3. Convergent EvolutionProcess by which unrelated organisms independently evolve similarities when adapting to similar environmentsEx: penguin (bird), shark (fish) and dolphin (mammal) all develop streamline bodies and swimming appendagesAnalogous structures: structures that look and function the same but have no common evolutionary history

4. CoevolutionProcess by which two species evolve in response to changes in each otherEx: 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 changeDarwin 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 changesEx: ancient insects= wings on all body segments and modern insects have wings on only 1 or 2 segments