Chapter 17

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.

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

Begins with Precambrian Time ( mya) Then broken into eras which are then divided into periods Precambrian Time ( mya) 90% of Earth’s history Life existed only in the sea

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

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

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

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

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 Ex. Plants have evolved poisons in response to insect attacks – some insects eventually were able to alter the poison

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.

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. Protenoid microspheres formed. Where encased in a membrane which allowed internal environment to differ from external.

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.