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 prokaryotes Learn 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 Period Age of the Fishes (sharks) First vertebrates on land (amphibians) Carboniferous and Permian Periods Reptiles evolve from amphibians Mass extinction: occurs when many organisms die out at the same time

Mesozoic Era Characterized by dinosaurs and flowering plants Triassic Period Age of the reptiles Dinosaurs First mammals (small shrews) Jurassic Period When dinosaurs ruled the earth… First bird- Archaeopteryx

Mesozoic Era (cont.) Cretaceous Period T-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 survivors Usually 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 Plans Remember 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