UVA BIOL 2200 Lessons 8-9 Textbook Notes

L8&9 Textbook Notes: The History of Life on Earth (C25) origin of life • it is hypothesized that chemical and physical processes could have produced simple cells through the sequence of four stages: 1. the abiotic synthesis of small organic molecules, such as amino acids and nitrogenous bases 2. the joining of these small molecules into macromolecules, such as proteins and nucleic acids 3. the packaging of these molecules into protocells, droplets with membranes that maintained an internal chemistry different from that of their surroundings 4. the origin of self-replicating molecules that eventually made inheritance possible synthesis of organic compounds on early earth • water vapor condensed into oceans • organic compounds formed from simpler molecules in reducing environment • energy came from lightning and uv rays • oparin-haldane hypothesis: oceans were a “primitive soup” from which life arose • miller/urey experiments supported this • experiments in neutral atmospheres also yielded organic molecules • first organic compounds could have been made in the reducing atmosphere of volcanoes; more were made in this simulation • organic compounds could have been first produced in hydrothermal or alkaline vents, the latter being more mild and suitable for life • meteorites might have been another source of organic molecules abiotic synthesis of macromolecules • the abiotic synthesis of rna’s two purine bases, adenine and guanine, can occur spontaneously from simple precursor molecules • the abiotic synthesis of cytosine and uracil was also accomplished • without enzymes or ribosomes, polymers can form spontaneously when amino acid or rna nucleotide solutions are ripped onto hot sand, clay, or rock (surfaces on which organic molecules become concentrated) protocells • self-replicating molecules and a metabolic source of building blocks could have appeared in early protocells • necessary conditions may have been met in vesicles, which can form when lipids or other organic molecules are added to water • vesicles can reproduce and grow on their own self-replicating rna • rna was most likely the first genetic material • ribozymes: rna catalysts that can make complementary copies of short pieces of rna with nucleotide building blocks • single-stranded rna molecules with certain nucleotide sequences can efficiently replicate natural selection leaves the most descendant molecules • • protocells: daughters of vesicles with self-replicating, catalytic rna • the most successful protocells would have passed their traits onto the following generations • once rna sequences with genetic information appeared on protocells: • dna would have a template to assemble nucleotides on, making a more chemically stable repository for genetic information • dna could replicate more accurately the fossil record • strata: sequence in which fossils accumulated in sedimentary layers the fossil record favors species that existed for a long time, were • abundant, and had hard shells/skeletons dating rocks and fossils • radiometric dating: based on the decay of radioactive isotopes • half-life: the time required for half of the parent isotope to decay the ratio of carbon-14, which starts to decay into nitrogen-14, to • carbon-12, which does not change over time, is measured older organisms are dated with the ages of surrounding volcanic layers • the origin of new groups of organisms • unique anatomical features allow classes to have their origins traced • mammals have a lower jaw composed of one bone • mammals have three bones that transmit sound in the middle ear • the teeth of mammals are differentiated the first single-celled organisms • the first organisms were single celled prokaryotes in teh ocean • the earliest evidence is from stromatolites stromatolites: layered rocks that form when certain prokaryotes • bind thin films of sediment together • sole inhabitants for 1.5 billion years photosynthesis and the oxygen revolution • o2 likely dissolved in the water and: • reacted with other elements to make precipitate • saturated seas and lakes • gassed out and entered the atmosphere • oxygen revolution: rapid increase from 1-10% of oxygen levels • could have extinguished many prokaryotic groups, leaving anaerobic species • adaptations evolved, such as cellular respiration the first eukaryotes • the oldest are single-celled organisms from 1.8 million years ago • had a nuclear envelope, mitochondria, endoplasmic reticulum, welldeveloped cytoskeleton, etc. • originated from endosymbiosis, when a prokaryotic cell engulfed a small cell that would involve into the mitochondrion • the smaller cell is an endosymbiont, a cell that lives within a host cell • serial endosymbiosis hypothesis: mitochondria evolved before plastids through a sequence of endosymbiotic events • plastids: chloroplasts and related organelles; made from an engulfed photosynthetic bacterium early multicellular eukaryotes • emerged about 1.3 billion years ago • larger and more diverse eukaryotes (ediacaran biota) appeared 600 million years ago • mostly soft-bodied organisms, including algae and animals the cambrian explosion • many present-day animal phyla appeared in fossils from 525-535 million years ago • some fossils of animal groups appeared in rocks from the late proterozoic, such as sponges, cnidarians, and molluscs • animals became predators rather than grazers, filter feeders, and scavengers • animals originated about 700 million years ago and remained small for over 100 million years before diversifying during the cambrian the colonization of land • prokaryotes lived in land 3.2 billion years ago, but larger forms of life did not until 500 million years ago • made possible with adaptations to reproduce on land and prevent dehydration (ex. vascular system in plants) • arthropods were the first to colonize land 450 million years ago • the earliest tetrapod was from 365 million years ago • the human lineage diverged 7-8 million years ago plate tectonics • the continents are part of plates of earth’s crust that float on the hot, underlying portion of the mantle • continental drift: process in which plates move over time consequences of continental drift • alters the habitats in which organisms live by altering the environment and climate • some species go extinct, and others have opportunities after survival • organisms can adapt, move to a new location, or go extinct • promotes allopatric speciation and explained geographic distributions of extinct organisms mass extinctions • the origin of one species can be detrimental to another • mass extinction: large numbers of species become extinct worldwide the “big five” mass extinction events • in each, at least half of marine species became extinct • in the permian mass extinction, 96% of marine animal species went extinct and highly affected terrestrial life • occurred in less than 500,000 years • volcanic eruption caused destruction through lava and high co2 levels • the cretaceous mass extinction took out more than half of all marine species and eliminated many families of terrestrial plants and animals • 66 million years ago • an asteroid is thought to have collided with earth, with the resulting cloud of debris blocking sunlight potential sixth mass extinction • human actions have threatened species with extinction • more than 1,000 species have become extinct in the last 400 years • hard to predict or document because of unknown species • harm is not near that of the previous mass extinctions • a human-caused mass extinction can occur in the next few centuries consequences of mass extinctions • once an evolutionary lineage disappears, it cannot reappear • it takes about 5-10 million years for the diversity of life to recover to previous levels after a mass extinction • the types of organisms can change, such as predators • the development of beneficial traits can be cut short adaptive radiations • adaptive radiations: periods of evolutionary change in which groups of organisms form many new species, whose adaptations allow them to fill different ecological roles/niches in their communities • large-scale adaptive radiations occur after mass extinctions, when survivors adapt to the vacant niches • increased the diversity of life in the past 250 years • one species that undergoes adaptive radiation can benefit another, such as by being a food source regional adaptive radiations • can occur when a few organisms go to a new, often distant location with little competition • physical diversity of the land can lead to speciation and evolutionary divergence by natural selection effect of developmental genes • slight genetic differences can produce major morphological differences between species changes in rate and timing • heterochrony: an evolutionary change in the rate or timing of developmental events • the cause of many striking evolutionary transformations; an organism’s shape depends on the relative growth rate of different body parts during development • increased or decreased growth can lead to the amplification or reduction of homologous traits • paedomorphosis: when the sexually mature stage of a species retains body features that were juvenile structures in an ancestral species changes in spatial pattern • homeotic genes: determine where parts will develop on an organism • hox genes: provide positional information in an animal embryo the evolution of development • selection can rapidly improve adaptations • new genes can take on new metabolic and structural functions, as can existing genes that are regulated in new ways changes in gene sequence • new developmental genes arising after gene duplication events likely facilitated the origin of newer morphological forms • nucleotide sequence of a developmental gene can cause a major evolutionary change changes in gene regulation • changes in sequence can affect a gene’s function wherever expressed • changes in the regulation of gene expression is limited to one cell type • because regulation may have fewer harmful side effects, they might more often cause changes in organisms’ forms • altering the expression of a developmental gene in only some parts of the body can cause morphological change evolutionary novelties • as new species form, novel and complex structures can arise as gradual modifications of ancestral structures • ex. only “simpler” eyes were needed in past organisms, such as to distinguish light from dark • traits evolve through a series of steps that benefited the organism at every stage • evolutionary novelties can arise when structures acquire a new role • exaptations: structures that evolve in one context but become coopted for another function • natural selection can only improve a structure in the context of its current utility, not in anticipation of future use evolutionary trends • branching evolution can result in a real evolutionary trends, even if some species do not follow it • species that endure the longest and generate the most offspring species (species selection) determine the direction of major evolutionary trends • there is no intrinsic drive toward a particular phenotype, as evolution is the result of interactions between current organisms and environments