Download EVOLUTION Name_______________________ Early scientists

EVOLUTION
Name_______________________
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Early scientists proposed ideas about evolution.
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Evolution is
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A species is
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There were many important naturalists in the 18th century.
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Linnaeus:
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Buffon: species shared ancestors rather than arising separately
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E. Darwin: more-complex forms developed from less-complex forms
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Lamarck:
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Theories of geologic change set the stage for Darwin’s theory.
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There were three theories of geologic change.---Catastrophism---Gradualism--uniformitarianism
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The theory of catastrophism states that
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Gradualism
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The theory of uniformitarianism states that
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Fossils
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Uniformitarianism is the prevailing theory of geologic change.
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Darwin observed differences among island species. Darwin’s voyage provided insight on evolution.
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Variation
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Galápagos tortoises that live in areas with tall plants have long necks and legs.
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Galápagos finches that live in areas with hard-shelled nuts have strong beaks.
An adaptation
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Species are able to adapt to their environment.
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Adaptations can lead to genetic change in a population.
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Darwin observed fossil and geologic evidence supporting an ancient Earth.
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Darwin found fossils of extinct animals that resemble modern animals.
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Darwin found fossil shells high up in the Andes mountains.
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He saw land move from underwater to above sea level due to an earthquake.
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Darwin extended his observations to the evolution of organisms.
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Darwin noticed a lot of variation in domesticated plants and animals.
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Artificial selection
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Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more
offspring on average than do other individuals.
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Natural selection explains how evolution can occur.
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Heritability
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There is a struggle for survival due to overpopulation and limited resources.
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Darwin proposed that adaptations arose over many generations.
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Natural selection explains how evolution can occur.
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There are four main principles to the theory of natural selection.
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Natural selection acts on existing variation.
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Natural selection can act only on traits that already exist.
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Structures take on new functions in addition to their original function.
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A population is
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Fitness
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Evidence of common ancestry among species comes from many sources.
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Fossils in older layers are more primitive than those in the upper layers.
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Biogeography is
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The study of geography provides evidence of evolution.
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island species most closely resemble nearest mainland species
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populations can show variation from one island to another
Embryology provides evidence of evolution.
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identical larvae, different adult body forms
--similar embryos, diverse organisms
The study of anatomy provides evidence of evolution.
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Homologous structures
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Homologous structures are evidence of a common ancestor.
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Analogous structures
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Analogous structures are not evidence of a common ancestor.
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Structural patterns are clues to the history of a species.
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Vestigial structures are
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Ostrich wings are examples of vestigial structures.
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Fossils provide a record of evolution.
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Paleontology
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Paleontology provides evidence to support evolution.
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Molecular and genetic evidence support fossil and anatomical evidence.
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Two closely-related organisms will have similar DNA sequences.
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Pseudogenes are sequences providing evidence of evolution.
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no longer function
--carried along with functional DNA
--can be clues to a common ancestor
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Evolution unites all fields of biology.
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Scientist from any fields contribute to the understanding of evolution.
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The basic principles of evolution are used in many scientific fields.
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A population shares a common gene pool.
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Genetic variation in a population increases the chance that some individuals will survive.
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Phenotypic variation is necessary for natural selection.
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Genetic variation is stored in a population’s gene pool.
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--allele combinations form when organisms have offspring
Allele frequencies measure genetic variation.
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made up of all alleles in a population
measures how common allele is in population
--can be calculated for each allele in gene pool
Genetic variation comes from several sources.
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can form new allele
-- can be passed on to offspring if in reproductive cells
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Recombination forms new combinations of alleles.
– usually occurs during meiosis
-- parents’ alleles arranged in new ways in gametes
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Hybridization is the crossing of two different species.
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occurs when individuals can’t find mate of own species
--topic of current scientific research
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Populations, not individuals, evolve. Natural selection acts on distributions of traits.
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A normal distribution graphs as a bell-shaped curve.
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highest frequency near mean value
Sketch the graph
-- frequencies decrease toward each extreme value
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Traits not undergoing natural selection have a normal distribution.
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Natural selection can change the distribution of a trait in one of three ways.
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Microevolution is evolution within a population.
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observable change in the allele frequencies
-- can result from natural selection
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Natural selection can take one of three paths.
Sketch the graphs
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Directional selection favors phenotypes at one extreme.
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Stabilizing selection favors the intermediate phenotype.
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Disruptive selection favors both extreme phenotypes.
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Natural selection is not the only mechanism through which populations evolve. Gene flow is the movement
of alleles between populations.
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Gene flow occurs when individuals join new populations and reproduce.
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Low gene flow increases the chance that two populations will evolve into different species.
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Genetic drift is a change in allele frequencies due to chance.
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It is most common in small populations.
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A population bottleneck can lead to genetic drift.
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It occurs when an event drastically reduces population size.
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The bottleneck effect is genetic drift that occurs after a bottleneck event.
The founding of a small population can lead to genetic drift.
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The founder effect is genetic drift that occurs after start of new population.
Genetic drift has negative effects on a population.
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less likely to have some individuals that can adapt
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Sexual selection occurs when certain traits increase mating success.
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males produce many sperm continuously
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females are more limited in potential offspring each cycle
There are two types of sexual selection.
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intrasexual selection:
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intersexual selection: males display certain traits to females
Hardy-Weinberg equilibrium describes populations that are not evolving.
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Biologists use models to study populations.
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Genotype frequencies stay the same if five conditions are met.
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very large population: no genetic drift
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no mutations: no new alleles added to gene pool
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no natural selection: all traits aid equally in survival
--no emigration or immigration: no gene flow
--random mating: no sexual selection
Real populations rarely meet all five conditions.
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Real population data is compared to a model.
--Models are used to studying how populations evolve.
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The Hardy-Weinberg equation is used to predict genotype frequencies in a population.
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Predicted genotype frequencies are compared with actual frequencies.
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used for traits in simple dominant-recessive systems
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must know frequency of recessive homozygotes
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There are five factors that can lead to evolution.
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Genetic drift
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Gene flow
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Mutations
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Sexual selection
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Natural selection
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In nature, populations evolve.
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expected in all populations most of the time
--p2 + 2pq + q2 = 1
-respond to changing environments
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The isolation of populations can lead to speciation.
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Populations become isolated when there is no gene flow.
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Isolated populations adapt to their own environments.
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Reproductive isolation can occur between isolated populations.
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members of different populations cannot mate successfully
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Speciation is
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Populations can become isolated in several ways.
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Behavioral barriers can cause isolation.
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-includes differences in courtship or mating behaviors
Geographic barriers can cause isolation.
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called behavioral isolation
-final step to becoming separate species
called geographic isolation
-physical barriers divide population
Temporal barriers can cause isolation.
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called temporal isolation
-timing of reproductive periods prevents mating
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Evolution occurs in patterns. Evolution through natural selection is not random.
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Natural selection can have direction.
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The effects of natural selection add up over time.
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Convergent evolution
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Divergent evolution
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Species can shape each other over time.
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Two or more species can evolve together through coevolution.
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evolutionary paths become connected
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Coevolution can occur in beneficial relationships.
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Coevolution can occur in competitive relationships.
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Species can become extinct.
-species evolved in response to changes in each other
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Background extinctions occur continuously at a very low rate.
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usually affects a few species in a small area
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caused by local changes in environment
Mass extinctions are rare but much more intense.
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destroy many species at global level
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at least five mass extinctions in last 600 million years
Speciation often occurs in patterns.
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theory proposed by Eldredge and Gould in 1972
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episodes of speciation occur suddenly in geologic time
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followed by long periods of little evolutionary change
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revised Darwin’s idea that species arose through gradual transformations
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ancestral species diversifies into many descendent species
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descendent species usually adapted to wide range of environments
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Specific environmental conditions are necessary in order for fossils to form.
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Fossils can form in several ways.
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Permineralization occurs when minerals carried by water are deposited around a hard structure.
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A natural cast forms when flowing water removes all of the original tissue, leaving an impression.
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Trace fossils record the activity of an organism.
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Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.
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Preserved remains form when an entire organism becomes encased in material such as ice.
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Specific conditions are needed for fossilization.
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Radiometric dating provides an accurate way to estimate the age of fossils.
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It compares the placement of fossils in layers of rock.
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Scientists infer the order in which species existed.
Radiometric dating uses decay of unstable isotopes.
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Isotopes are atoms of an element that differ in their number of neutrons.
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A half-life is the amount of time it takes for half of the isotope to decay.
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The geologic time scale divides Earth’s history based on major past events.
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Index fossils can provide the relative age of a rock layer.
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existed only during specific spans of time
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Index fossils include fusulinids and trilobites.
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The geologic time scale organizes Earth’s history.
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Eras last tens to hundreds of millions of years.
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consist of two or more periods
-occurred in large geographic areas
-three eras: Cenozoic, Mesozoic, Paleozoic
Periods last tens of millions of years.
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most commonly used units of time on time scale
-associated with rock systems
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Epochs last several million years.
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The origin of life on Earth remains a puzzle. Earth was very different billions of years ago.
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There have been many hypotheses of Earth’s origins.
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The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis.
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Several sets of hypotheses propose how life began on Earth.
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There are two organic molecule hypotheses.
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0meteorite hypothesis
There are different hypotheses of early cell structure.
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Miller-Urey experiment
iron-sulfide bubbles hypothesis
-lipid membrane hypothesis
A hypothesis proposes that RNA was the first genetic material.
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Ribozymes are RNA molecules that catalyze their own replication.
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DNA needs enzymes to replicate itself.
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Single-celled organisms existed 3.8 billion years ago. Microbes have changed the physical and chemical
composition of Earth.
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The oldest known fossils are a group of marine cyanobacteria.
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prokaryotic cells
-added oxygen to atmosphere
-deposited minerals
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Fossil stromatolites provide evidence of early colonies of life.
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Eukaryotic cells may have evolved through endosymbiosis.
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Endosymbiosis is a relationship in which one organism lives within the body of another.
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Mitochondria and chloroplasts may have developed through endosymbiosis.
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The evolution of sexual reproduction led to increased diversity.
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Sexual reproduction may have led to the evolution of multicellular life.
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Multicellular life evolved in distinct phases.
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Multicellular organisms first appeared during the Paleozoic era.
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The era began 544 million years ago and ended 248 million years ago.
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The Cambrian explosion led to a huge diversity of animal species.
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Life moved onto land in the middle of the Paleozoic era
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Reptiles radiated during the Mesozoic era.
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The Mesozoic era is known as the Age of Reptiles.
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It began 248 million years ago and ended 65 million years ago.
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Dinosaurs, birds, flowering plants, and first mammals appeared.
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Mammals radiated during the Cenozoic era.
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The Cenozoic era began 65 million years ago and continues today.
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Placental mammals and monotremes evolved and diversified.
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Anatomically modern humans appeared late in the era.
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Humans appeared late in Earth’s history. Humans share a common ancestor with other primates.
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Primates evolved into prosimians and anthropoids.
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Prosimians are the oldest living primates.
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Anthropoids are humanlike primates.
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They are subdivided into the New World monkeys, Old World monkeys, and hominoids.
-they are mostly small and nocturnal
Homonoids are divided into hominids, great apes, and lesser apes.
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Bipedal means walking on two legs.
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Foraging
-carrying infants and food
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Walking upright has important adaptive advantages.
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There are many fossils of extinct hominids.
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Most hominids are either the genus Australopithecus or Homo.
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Australopithecines were a successful genus.
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The Homo genus first evolved 2.4 million years ago.
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Modern humans arose about 200,000 years ago.
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Homo sapiens fossils date to 200,000 years ago.
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Human evolution is influenced by a tool-based culture.
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There is a trend toward increased brain size in hominids.
-using tools
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