Ch 17 The History of Life

1. Ch 17 The History of Life

2. Ch 17.1 – The Fossil Record • Paleontologists- scientists who study fossils • Fossil record • Provides evidence about the history of life • Shows how different groups of organisms have changed over time • 99% of species ever to have lived on earth are extinct (species died out)

3. How fossils form • Fossils can be: • Entire preserved animals • Small pieces like fragments of bone or leaves • Eggs, footprints, animal droppings, pollen, shells, wood • 1. Particles of sand and rock are brought to water and settle to the bottom • 2. Dead organisms are buried by layers of sediment, which forms new rock • 3. Over time, the layers are compressed and the remains are left to be found many years later.

4. Shells Insects Bones

5. Interpreting Fossil Evidence • Natural forces cause the Earth to lift rocks up in a mountain range, or erode rocks down by wind or water. • To determine the age of fossils paleontologists use: • Relative dating – age of a fossil compared with that of other fossils in other layers of rock (oldest layer on the bottom) • Index Fossils- easily recognized organisms who existed for a short period of time but had a wide geographic distribution

7. To determine the age of fossils, scientists also use: • Radioactive dating – some fossils have radioactive elements in the rocks • Half life – length of time required for half of the radioactive atoms in a sample to decay • Scientists use half-life to determine age of fossil by determining how much of the radioactive isotope remains • Common elements: Carbon-14 =5730 years

8. Geologic Time Scale- represents evolutionary time • Scientists used the major changes found in the animals and plants to mark where one segment of time ends and the next begins • Precambrian • Paleozoic- lasted 300 million years • Mass extinction • Mesozoic- lasted 180 million years • Dinosaurs • Cenozoic- started 65 million years ago and continues to the present • Humans

10. Earth’s Early History • Earth’s early atmosphere probably made up of hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water • About 3.8 billion years ago, Earth cooled enough for water to remain liquid. The earliest sedimentary rocks have been dated to this period.

11. Miller and Urey’s Experiments • 1950’s Stanley Miller and Harold Urey • Tried to determine if organic compounds could have formed under the conditions of early Earth. • They passed electric sparks through a mixture of hydrogen, methane, ammonia, and water • After a few days, several amino acids (the building blocks of proteins) were formed • We now know that their ideas about Earth’s early atmosphere were not accurate, but experiments based on current knowledge have produced organic compounds.

12. Rise of oxygen • Microfossils of single-celled prokaryotes have been found in rocks more than 3.5 billion years old • By 2.2 billion years ago fossil evidence indicates that photosynthetic bacteria became common, producing oxygen • Rise of oxygen in the atmosphere drove some life forms to extinction, while others evolved new, more efficient metabolic pathways that used oxygen for respiration.

13. Endosymbiotic Theory • According to the Endosymbiotic Theory eukaryotic cells formed from a symbiosis among several different prokaryotic organisms. • Evidence: Shared traits by Mitochondria, Chloroplasts, and Bacteria: similar type of DNA, similar ribosomes, and reproduction by binary fission.

14. Evolution of Multicellular Life • Precambrian Time • 90% of Earth’s history occurred during this time frame • Anaerobic forms of life appeared  Then photosynthetic life, which added oxygen  Then aerobic life and eukaryotes  Then multicellular organisms which got more complex with time • Few fossils because animals were soft bodied • Life only existed in the sea!

16. Paleozoic Era • Diversity of marine life • More fossil evidence • Diversification of life led to groups like invertebrates, brachiopods (orgs with 2 shells) and trilobites (arthropods) • Age of Fishes- bony skeleton fish with jaws and eventually sharks • Fish began to crawl on land amphibians • Amphibians reptiles • Insects, and many plant varieties • Mass extinction eliminated about 95% of the complex marine organisms as well as land plants and animals

17. Dunkleosteus

18. Mesozoic Era • “Age of Reptiles” • Dinosaurs and the appearance of flowering plants • Dinosaurs started as carnivores • Archaeopteryx – a flying dinosaur relative makes the connection between birds and reptiles • Flying reptiles went extinct, but some swimming reptiles showed up • Another mass extinction wiped out half all plant and animals including the dinosaurs

20. Cenozoic Era • “Age of Mammals” • Mammals began to adapt to live on land, in water and in the air • Climate was warm and mild • Marine mammals, flowering plants, insects, grasses grazing animals • Ice ages covered parts of Europe and N. America • 20,000 years ago temperatures began to warm • Diversity of life thrived • First fossil evidence of our species Homo sapiens appeared around 200,000 years ago

23. Patterns of Evolution • Extinction– disappearance of a species; several mass extinctions have occurred; due to large volcanic eruptions, continents moving, & sea levels changing • Adaptive Radiation – process where a single species evolves into several different forms that live in different ways through natural selection • Example: In Lake Victoria, an isolated lake which formed recently in the African rift valley, over 300 species of cichlid fish adaptively radiated from one parent species in just 15,000 years

24. Patterns of Evolution • Convergent Evolution • Process when unrelated organisms come to resemble one another • Ex: sharks, dolphins, penguins, seals, fish • Coevolution • Process by which two species evolve in response to changes in each other over time

25. Rate of evolution • Punctuated equilibrium- long stable periods of time interrupted by brief periods of more rapid change • Gradualism- slow, steady change There is debate among scientists but it is obvious that evolution has proceeded at different rates for different organisms at different times.

27. Checkpoint! The process that produces a similar appearance among unrelated groups of organisms is: a. adaptive radiation c. convergent evolution b. coevolution d. mass evolution The acacia ant provides protection for the Swollen thorn acacia tree against preying insects, and the tree provides nourishment and shelter for the ant and the ants’ larvae. This is an example of: a. adaptive radiation c. convergent evolution b. coevolution d. mass evolution