Transcript Chapter 26
Overview Geologic events that alter environments change the course of biological evolution Example: Large lake splitting into several small lakes Living things change the planet they inhabit Example: Evolution of photosynthetic organisms putting oxygen into the atmosphere Photosynthetic Cyanobacteria 26.1 Cells produced in 4 stages 1. Abiotic synthesis of AA & nucleotides (organic compounds) 2. Joining of monomers into polymers 3. Packaging into protobionts – droplets with membranes that maintained an internal chemistry different from the environment. 4. Origin of replication that made inheritance possible Evidence for each of these 4 stages discussed 1. Synthesis of organic compounds Earth formed about 4.6 billion years ago Conditions on early Earth were very different from today “Primitive soup” experiment of Miller and Urey Strongly reducing atmosphere Hydrogen Methane Ammonia Water vapor Sparks to mimic lightning Conception of Earth 3 billion years ago Extraterrestrial Sources of Organic Compounds Amino acids that reached early Earth aboard chondrites could have added to the primitive soup Looking to other planets for signs of life Present day Mars = no life Billions of years ago it was warm, liquid water, and carbon dioxide in the atmosphere 2. Abiotic synthesis of polymers Researchers have produced amino acids polymers by dripping solutions of amino acid monomers onto hot sand, clay, or rock Formed spontaneously 3. Protobionts Replication and metabolism are essential for life Protobionts: aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure. Exhibit some properties of life and could have formed from abiotically produced organic compounds 4. Origin of replication The first genetic material was probably RNA Had the ability to copy itself and began to appear in protobionts RNA could have been the template on which DNA was assembled DNA is much more stable and can be replicated more accurately so as genomes grew DNA grew RNA world gave way to a DNA world and RNA took over its role that we see it in today 26.2 The fossil record Fossils are found in sedimentary rocks Index fossils: the strata at one location can often be correlated with strata at another location by the presence of similar fossils known as index fossils Radiometric dating Radiometric dating: decay of radioactive isotopes Half-life: the number or years it takes for 50% of the original sample to decay Carbon-14 has a half life of 5,730 years so it is useful for dating fossils up to about 75,000 years old Potassium-40 used to date much older fossils (530 million years old) Magnetism of rocks can also provide dating information Geologic record 3 Eons Archaean & Proterozoic lasted approx. 4 billion years These are known as Precambrian Phanerozoic eon –the last half billion years is most of the time multicellular eukaryotic life has existed Divided into 3 eras Paleozoic Mesozoic Cenozoic Boundaries between eras correspond to times of mass extinctions seen clearly in the fossil record Mass Extinctions 2 mass extinctions have received the most attention Permian & Cretaceous Permian – at the boundary between Paleozoic and Mesozoic eras claimed about 96% of marine animal speices Cretaceous – at the boundary between Mesozoic and Cenozoic eras doomed more than half of all marine species and many families of terrestrial plants and animals including the dinosaurs. Permian mass extinction caused by volcanic eruptions that increased the carbon dioxide and warmed the global climate Cretaceous mass extinction caused by an asteroid or comet hitting the earth that spewed up dust and blocked sunlight for several months. Impact Crater 26.3 Oldest known fossils Date to 3.5 billion years ago Stromatolites Composed of layers of bacteria and sediment Found today in a few warm, shallow, salty bays Prokaryotes Prokaryotes were Earth’s sole inhabitants 3.5 to about 2 billion years ago The oxygen revolution Earliest types of photosynthesis did not produce oxygen Oxygenic photosynthesis evolved 3.5 billion years ago in cyanobacteria When oxygen started to accumulate in atmosphere It posed a challenge for life It provided an opportunity to gain abundant energy from light It provided organisms an opportunity to exploit new ecosystems 26.4 – Eukaryotes Oldest fossil eukaryotes date back 2.1 billion years Arose from Endosymbiosis and genetic exchanges between prokaryotes Endosymbiotic theory states that chloroplasts & mitochondria were formerly prokaryotic organisms living within larger cells. Endosymbiosis Mitochondria and plastids were formerly small prokaryotes living within larger host cells Gained entry to the host cell as undigested prey or internal parasites The host and endosymbionts would have become a single organism Evidence to support theory: Similarities in inner membrane structures and functions Both have their own circular DNA 26.5 - Multicellularity Evolved several times in eukaryotes Oldest fossils of eukaryotes, small algae that lived 1.2 billion years ago 1st multicellular organisms were colonies Cambrian Explosion Most of the major phyla of animals appear here Colonization of land by plants, fungi, and animals Occurred about 500 million years ago Adaptations that helped prevent dehydration made it possible to move out of water onto land Symbiotic relationships between plants and fungi began at this time and exist today Continental Drift Continents are not fixed but drift across our planet’s surface on plates of crust that float on a hot underlying mantle Interactions at plate boundaries Convergent boundaries (moving together) Divergent boundaries (moving apart) Transform boundaries (sliding past one another) Volcanoes, Earthquakes, mountain building, and subduction occur at plate boundaries The formation and breakup of the supercontinent Pangaea explain many biogeographical puzzles Land bridges Fossils found on 2 continents that can’t swim Rock formations Apparent puzzle piece fit of the continents 26.6 Taxonomic systems Old system was 2 Kingdoms (Plant & Animal) 5 kingdom system Monera, Protists, Plantae, Fungi, Animalia 3 Domain system has replaced the 5 kingdom system Archaea, Bacteria, Eukarya