The History of Life

1. The History of Life Chapter 17

2. Fossil Record • Paleontologists – study fossils • Infer an organism’s structure, diet, and where they lived • Fossil record – shows how organisms changed over time • >99% of all species that have ever lived are extinct (died out) • Formation – most found in sedimentary rock • Particles of rock, sand, and clay are carried by water and settle at the bottom of oceans and rivers. • Organisms that die also sink to the bottom where they are covered as more rock material sinks. • The weight and pressure increase over time and turn the particles into rock.

3. Other fossils are formed when an entire organism is covered by ice or amber. • 2 techniques to determine age • Relative dating – look at what layer of strata the fossil is found in • Usually deeper = older • Radioactive dating (absolute dating) – uses the half-life of a radioactive isotope • Half-life – amt of time required for ½ the atoms in a radioactive sample to decay • Much more accurate • Ex. Carbon-14 half-life = 5730 years • Useful for fossils younger than 60,000 years old • Use potassium-40 (half-life = 1.26 billion years) for older fossils

5. Geologic Time Scale • Begins w/ Precambrian Time (650-544 mya) • Then broken into eras which are then divided into periods • Precambrian Time (650-544 mya) • 90% of Earth’s history • Life existed only in the sea

6. Paleozoic era • 544-245 mya – paleo = old; zoic = life • Cambrian • Cambrian explosion – diversification of life • Organisms with hard body parts appeared • Life still in the ocean • Ordovician and Silurian • Invertebrates and plants began to appear on land • Devonian • Age of fishes – due to thriving life in the oceans • Appearance of sharks • Appearance of insects • Vertebrates appeared on land • Carboniferous and Permian • Life spread out over land. • Reptiles • Swampy forests (sediment eventually produced coal) • Permian Extinction – 95% of life died out

7. Mesozoic era • 245-65 mya – Age of Dinosaurs – meso = middle • Triassic • Dinosaurs and mammals appeared • Jurassic • Land ruled by dinos • Archaeopteryx appeared – 1st bird • Cretaceous • T-rex • Flowering plants • Cretaceous Extinction – death of the dinos • 50% of life died out

8. Cenozoic era • 65-present – Age of Mammals – ceno = recent • Tertiary • Whales and dolphins appeared • Grasses evolved – led to grazing animals • Quaternary • Series of ice ages

9. Macroevolution • Large-scale evolution – 6 patterns of evolution • Extinctions • Mass extinctions left habitats wide open for those left to evolve and fill. • Ex. Dinosaur extinction allowed mammals to thrive. • Adaptive radiation • A species evolves into different forms based on environment. • Ex. Galapagos finches and tortoises

10. Macroevolution cont. • Convergent evolution • Unrelated organisms become similar. • Ex. Sharks, dolphins, penguins, seals • Coevolution • 2 species evolve in response to each other over time • Ex. Orchid and hawk moth; cactus and bat • Ex. Plants have evolved poisons in response to insect attacks – some insects eventually were able to alter the poison

11. Macroevolution cont. • Punctuated equilibrium • Long, stable periods interrupted by brief periods of rapid change • Can be caused by: • Isolation of small portions of the population – changes spread more quickly with fewer organisms or they evolve to fill all niches • Mass extinctions – leave open many niches to be filled • Developmental genes and body plans • Hox genes – control development of important body structures • Turning the genes on/off can produce major changes in body plan • Ex. Ancient insects had wings on every segment. Today’s insects have wings on only 1 or 2 segments.

12. Earth’s history • Early atmosphere was most likely made up of hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. • Stanley and Urey • Experimented with the early atmosphere to see if life could have been produced when electricity and uv radiation were present. • Experiment did produce amino acids and nitrogen bases. • Protenoidmicrospheres formed. • Where encased in a membrane which allowed internal environment to differ from external.

13. Earth’s history cont. • Believe RNA was the first genetic material. • Ancestors of photosynthetic cyanobacteria began to produce oxygen. • As the amt in the atmosphere increased many organisms died. • Allowed new metabolic pathways to form. • Eukaryotic cells formed. • Endosymbiotic theory – prokaryotic cells began to live symbiotically (each helping the other) and eventually one cell completely took over the other • Believe the first organelles were the mitochondria.

15. Isabella Island Pinta Island Hood Island

16. A B C