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analogous structures
[Gk. analogos, similar to one another] Dissimilar body parts that have become similar in structure, function, or both in lineages that are not closely related but were subjected to similar pressures.
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Archean eon
Eon extending from the time that life originated, 3.8 billion years ago, to 2.5 billion years ago.
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Cenozoic
The modern geologic era, from 65 million years ago to the present.
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comparative morphology
[Gk. morph, form] Scientific study of comparable external body parts of embryonic stages and adult forms of major lineages.
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evolution
[L. evolutio, an unrolling] Genetic change in a line of descent by microevolutionary events (gene mutation, natural selection, genetic drift, and gene flow); basis of large-scale patterns, rates, and trends in the history of life.
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fossilization
How fossils form over time. An organism or evidence of it gets buried in sediments or volcanic ash; water slowly infiltrates the remains, and metal ions and other inorganic compounds dissolved in it replace the minerals in bones and other hardened tissues.
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fossils
Recognizable, physical evidence of an organism that lived in the distant past.
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geologic time scale
Time scale for Earth�s history; major subdivisions correspond to mass extinctions. Dates are now absolute as a result of radiometrically dating.
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half-life
The unvarying time it takes for half of a quantity of any radioisotope to decay into a more stable form.
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inheritance of acquired characteristics
Transmission, from parents to offspring, of genes that underlie the traits characteristic of their species.
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macroevolution
Large-scale patterns, rates of change, and trends among lineages.
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Mesozoic
Era of spectacular expansion in the range of global diversity; lasted from 240 million to 65 million years ago.
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molecular clock
Model used to calculate the time of origin of one lineage relative to others; assumes that a group of genes accumulates mutations at a constant rate, measurable as a series of predictable ticks back through time. The last tick stops close to the time the lineage originated.
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morphological convergence
A pattern of macroevolution. In response to similar environmental pressures, body parts of evolutionarily distant lineages slowly evolve in similar ways and end up being alike in function, appearance, or both.
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morphological divergence
Pattern of macroevolution. One or more body parts of genetically diverging lineages undergo structural and functional changes from the parts in the common ancestor.
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natural selection
Microevolutionary process; the outcome of differences in survival and reproduction among individuals of a population that differ in the details of their heritable traits.
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nucleic acid hybridization
Any basepairing between DNA or RNA strands from different sources.
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Paleozoic
Era from 544 million to 248 million years ago; Cambrian through Permian.
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Pangea
Paleozoic supercontinent; the first land plants and animals evolved on it.
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plate tectonics theory
Theory that great slabs or plates of Earth�s outer layer float on a hot, semi-molten mantle. All plates are moving slowly and have rafted continents to new positions over time.
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Proterozoic
Era between 2.5 million to 544 million years ago. An oxygen-rich early atmosphere formed, sparking the Cambrian explosion of biodiversity.
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radiometric dating
Method of measuring proportions of a radioisotope in a mineral trapped long ago in newly formed rock and a daughter isotope that formed from it by radioactive decay in the same rock. Used to assign absolute dates to fossil-containing rocks and to the geologic time scale.
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species
[L. species, a kind] Of sexually reproducing species, one or more natural populations of individuals that successfully interbreed and are isolated reproductively from other such groups. By a cladistic definition, one or more natural populations of individuals with at least one unique trait derived a common ancestor that occurs in no other groups.
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stratification
Stacks of sedimentary rock layers, built up by deposition of silt and other materials over time.
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theory of uniformity
Theory that Earth�s surface has changed in slow, uniformly repetitive ways except for expected annual catastrophes, such as big floods. Changed Darwin�s view of evolution; has since been discredited by plate tectonics theory.
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