[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.
Eon extending from the time that life originated, 3.8 billion years ago, to 2.5 billion years ago.
The modern geologic era, from 65 million years ago to the present.
[Gk. morph, form] Scientific study of comparable external body parts of embryonic stages and adult forms of major lineages.
[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.
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.
Recognizable, physical evidence of an organism that lived in the distant past.
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.
The unvarying time it takes for half of a quantity of any radioisotope to decay into a more stable form.
inheritance of acquired characteristics
Transmission, from parents to offspring, of genes that underlie the traits characteristic of their species.
Line of descent.
Large-scale patterns, rates of change, and trends among lineages.
Era of spectacular expansion in the range of global diversity; lasted from 240 million to 65 million years ago.
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.
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.
Pattern of macroevolution. One or more body parts of genetically diverging lineages undergo structural and functional changes from the parts in the common ancestor.
Microevolutionary process; the outcome of differences in survival and reproduction among individuals of a population that differ in the details of their heritable traits.
nucleic acid hybridization
Any basepairing between DNA or RNA strands from different sources.
Era from 544 million to 248 million years ago; Cambrian through Permian.
Paleozoic supercontinent; the first land plants and animals evolved on it.
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.
Era between 2.5 million to 544 million years ago. An oxygen-rich early atmosphere formed, sparking the Cambrian explosion of biodiversity.
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.
[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.
Stacks of sedimentary rock layers, built up by deposition of silt and other materials over time.
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.