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BIOL 103
Virginia K Walker

BOAG WEEK 1 (CH. 20, page 489-494)(CH. 21): EVOLUTION + DIVERSITY CHAPTER 20: HISTORY OF LIFE ON EARTH Geological Timescale: timeline of the earth's history from its origin (4.55 billion years ago) to now -subdivided into 4 eons --> Pre-Cambrian: first 3 eons -further subdivided into many eras -the changes in living organisms are the result of 2 interactive processes 1. genetic changes in organisms can affect their characteristics -changes can affect organism's survival skills 2. Earth's environment has changed -environ changes influence the types of organisms that have existed during different periods -can set basis for new species to arrive and/or can cause extinction of a species Biological Changes + Extinctions are correlated w/ Major Environmental Changes: 1. Climate + Temperature -first 2.5 billion years was cool; last 2 billion years has seen great T fluctuations -ice ages, etc -T on earth isn't constant; produces areas with significantly different T (desert, arctic) 2. Atmosphere -chem composition of gasses on Earth has changed a lot -arrival of organisms capable of photosynthesis added Oxygen to the atmosphere 3. Land Masses -as earth cooled, land masses formed that were surrounded by bodies of water -created terrestrial + aquatic environments -major land masses (continents) have shifted positions, changed shapes, and separated from each other (continental drift) 4. Floods -catastrophic floods can cause extinction 5. Glaciation -glaciers have moved across continents and changed the compositions of species on those land masses -also affects water levels of oceans 6. Volcanic Eruptions -negatively affects species near the eruption; may cause extinction -near bodies of water: can lead to formation of new islands -debris in air can affect global T and limit solar radiation, limiting photosynthesis 7. Meteoritic Impacts -large meteorites have had substantial impacts on the Earth's environment 1+ of these events can cause many species to go extinct at a time: mass extinction -mass extinctions near the end of Ordovician, Devonian, Permian, Triassic, and Cretaceous periods -geological eras often defined by biological extinctions + adaptive activities of flora/fauna FOSSILS -recognizable remains of past life on earth -bones, shells, leaves, cell impressions, tracks, burrows -fossil record provides a record of the life forms that existed during particular geological periods -found in layers of the earth, tree amber (insects, seeds etc), etc -provides insight as to what kind of life was present during that period in time 1. many of the rocks w/ fossils are sedimentary: formed from particles of older rocks broken apart by water or wind; buries organisms at the bottoms of bodies of water once they settle 2. over time, more particles pile up, and sediments @ the bottom of the pile eventually become rock 3. rock particles conglomerate, sand becomes sandstone, and mud becomes shale 4. most fossils formed when organisms are buried quickly: during process of sedimentary rock formation, their hard parts are gradually replaced by minerals, producing an impression of the organism's structure that used to be there -sedimentary rocks formed particle by particle and bed by bed: the layers are piled on top of each other in strata -deeper strata holds ancient life, while upper strata holds newer life -radioisotope dating: way to estimate the age of a fossil -measures the amount of an isotope in a rock sample, and the amount of the isotope that is produced when the original isotope decays -isotope decay patterns useful for identification: C to N, K to Ar, Ru to Sr, U to Pb -dating usually isn't conducted on the fossil of sedimentary rock, but the igneous rock nearby -fossil record likely an underestimate of when a species arrived (unlikely to find first specimen of the species) Factors that Impart a Bias on Fossil Record 1. some organisms are more likely to become fossilized than others, based on thei anatomy, size, number, environ, time, etc 2. Geological processes can create bias b/c they may favour the fossilization of certain types of organisms -can cause confusion b/c they can mix parts of different species after death (eg. water current sweeps fish and reptile skeletons together 3. unintentional biases related to paleontologists: may search for one species in particular -fossil record isn't comprehensive or complete insight/log of life in the past Anatomy: hard organisms favoured for fossils Size: large organisms favoured Number: most abundant=bigger chance of fossilization Environment: aquatic/edge of water organisms more likely to be fossilized Geology: chem process of fossilization may favour certain organisms; organism bodies may be damaged/distorted Time: more likely to find a fossil of a recent animal than a very ancient animal Paleontology: certain types of fossils are searched for more; searches in only selection, specific areas PROKARYOTIC CELLS + ARCHEAN EON -diverse microbial life in ocean -first fossils were of prokaryotic cells -during the archean eon, all life forms were prokaryotic and anaerobic (barely an O2) -archaea came about in early extreme environments on earth (modern-day archaea are extremophiles (living in extreme conditions), methanogens, or non-extreme) -since bacteria + archaea are so similar, this indicates that they had a shared ancestor -Energy greatly influences emergence of prokaryotic + eukaryotic species -first prokaryotes were heterotrophs: would have been simpler for first ancestral cells to use organic molecules in prebiotic soup as food, rather than making E from inorganic molecules (autotrophs + photosynthesis) -prebiotic soup was made slowly; heterotrophs eventually ate all the organic compounds up -w/o organic food, cells evolved the ability to use photosynthesis (inorganic molecules) -however, first organism found was of autotrophic cyanobacteria: certain cyanos promote the formation of a layered structure called stromatolite; cyanos depleted CO2 in their area, causing lots of Ca2+ build-up to precipitate over the mat of cyano cells, fossilizing them Emergence + Proliferation of ancient Cyanos has Consequences: 1. autotrophic nature of these bacteria let them produce organic molecules from CO2 -prevented depletion of organic foods that would've exhausted if there were only heterotrophs 2. production of O2 as a waste product increased atmospheric O2 -anaerobic species became restricted to a few anoxic environments (eg. deep in soil) -O2 enabled formation of new aerobic prokaryotes + emergence of eukaryotic life CHAPTER 21: EVOLUTION Biological Evolution: heritable change in 1+ characteristics of a pop'n of species across many generations -small scale (microevolution; 1 or a few genes in a pop'n over time) or large scale (macroevolution; formation of a new species or groups of related species) Species: a group of related organisms that share a distinctive form Pop'n: members of the same species that are likely to encounter one another and so have the opportunity to interbreed Molecular evolution: the molecular changes in genetic material that underlie the phenotypic changes associated w/ evolution John Ray: established modern concept of a species -believed adaptation to be god's design; didn't believe in evolution Carolus Linnaeus: expanded upon the taxonomy system -didn't believe in evolution Baron Cuvier: argued against evolution; thought organisms were integrated wholes (if one thing changed, it'd upset the whole structure of the organism and it would die -Catastrophism: only catastrophic events changed the earth's geological structure; 6000 y.o. George Buffon: living things do change over time Jean-Baptiste LaMarck: suggested relationship b/w variation + evolution -by looking @ fossils, he noticed that some species had chanegs over time, while others remained the same -hypothesized that species change over many generations by adapting to new environ -believed that living things evolved in an upwards fashion: from dead matter to human "perfection" -organisms altered their behavior in response to environ changes -Inheritance of Acquired Characteristics: modified traits were inherited by offspring Uniformitarianism: changes in earth are directly caused by recurring events (eg. erosion, plate techtonics, etc) CHARLES DARWIN -found a variation of finches; ability to survive in their new island habitat depended on changes in the size and shape of their bills over many generations -specializations in features enabled succeeding generations to get food better NATURAL SELECTION -biological species don't have a fixed, static existence: exhibits changing traits over the course of generations -Darwin hypothesized that existing life forms on earth are the product of the modification of pre- existing life forms--> theory of descent w/ modification through variation and natural selection...based on: 1. variation in a given species -var
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