Geology Chapter 5 summary
Geology Chapter 5 summary GEOG-G105
Popular in Earth: our habitable planet
Popular in Geology
This 2 page Class Notes was uploaded by Bruce Kwon on Monday March 28, 2016. The Class Notes belongs to GEOG-G105 at Indiana University taught by Bruce Douglas in Spring 2016. Since its upload, it has received 11 views. For similar materials see Earth: our habitable planet in Geology at Indiana University.
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Date Created: 03/28/16
1. While some conditions at the earth's surface ( mean temperature) may have remained within modest limits for most of its history, others (oxygen concentrations) have undergone radical changes. Yet life has apparently been present almost throughout, although the main diversification of eukaryotes only occurred over the last 1000 Ma. 2. Stromatolites dominate all but the last part of the Proterozoic fossil record, reaching a peak around 1.0 Ga and declining thereafter. Exceptionally well-preserved early examples contain microfossils of tiny filamentous and spheroidal prokaryotes. By mid-Proterozoic times, there was a clear differentiation of communities in different habitats, including both prokaryotes and simple eukaryotes. Planktonic forms supplied organic material to the deep sea floor. 3. Fossils of probable eukaryotes show that they had evolved at least by the mid-Proterozoic (around 2.1 Ga). Organelles such as mitochondria and chloroplast probably evolved from endosymbiotic prokaryotes that took up residence in the ancestral eukaryotic cells. This nucleus, by contrast, probably evolved within the original cell structure. The acquisition of mitochondria might have been in response to the first appearance of molecular oxygen. 4. Both fossils and molecular data point to an evolutionary explosion of eukaryotes commencing between about 1.2 Ga and 1.0 Ga. This may reflect the evolution of sexual reproduction: no particular environmental trigger has been implicated 5. The last 70 Ma of the Proterozoic (the Ediacaran Period) was marked by the appearance of assemblages of large, enigmatic fossils collectively referred to as Ediacaran faunas. They have been subject to a variety of alternative interpretations, but most are likely to have been primitive animals. Molecular data confirm the existence of animals from about 1.0 Ga. 6. Eukaryote cell nuclei contain orders of magnitude more DNA in chromosomes than the simple loop attached to the inside of the rigid outer wall of prokaryote cells. The eukaryote cell also possesses an internal framework of protein rods, which can alter cell shape and control its internal structure. These differences have vastly expanded the relative scope of eukaryote evolution to include multicellularity with cell differentiation, allowing them to build up multi-tiered trophic pyramids. Prokaryotes, meanwhile, have been confined to production and decomposition, although under a wide range of conditions. 7. There is an increased probability of mutation associated with the increased amounts of DNA in eukaryotes. Compensation for this is provided by doubling of the chromosomes, together with the mixing of genes from different individuals through sexual reproduction. 8. Sexual reproduction has increased the efficacy of natural selection, potentially allowing all possible permutations of the genes available in the population to be tested in the struggle for existence. This allows even complex multicellular organisms with slow rates of reproduction to evolve rapidly. 9. Adaptations that evolve through natural selection remain of selfish benefit, in terms of fitness, to the individuals (or genetic entities) possessing them. adaptation may influence higher levels (population and ecosystems) but only by wat of incidental effect, which may be good or bad. Hence, while natural selection can explain adaptations for homeostasis in individuals, the theory does not predict the emergence of analogous systems at higher levels.