BIOL 100 Chapter Notes - Chapter 13: Vestigiality, Goose Bumps, Geologic Time Scale
Chapter 13: Evidence of Evolution
13.1 Clues to Evolution Lie in the Earth, Body Structures, and Molecules
•Paleontology: study of fossil remains or other clues to past life
•geologic timescale: life’s long evolutionary path that divides Earth’s history into a series of eons and
eras defined by major geological or biological events such as mass extinctions
13.2 Fossils Record Evolution
•Fossil: any evidence of an organism from more than 10,000 years ago
A. Fossils Form in Many Ways
•fossils form when an organism dies, becomes buried in sediments, and is chemically altered
•fossil fuels (coal, oil, and natural gas) are the decomposed remains of plants and other organisms
preserved by compression
B. The Fossil Record Is Often Incomplete
•vast majority of organisms never leave a fossil trace
•erosion or the movements of Earth’s continental plates have destroyed many fossils that did form
•scientists are unlikely to ever discover the many fossils that must be buried deep in the Earth or
submerged under water
C. The Age of a Fossil Can Be Estimated in Two Ways
•two general approaches used to estimate when a fossilized organism lived
1. Relative Dating: places a fossil into a sequence of events without assigning it a specific age
•usually based on principle of superposition, with lower rock strata presumed to be older than higher
layers
2. Absolute Dating: assigns age to fossil by testing either the fossil itself or the sediments above and
below the fossil
•Radiometric dating: type of absolute dating that uses radioactive isotopes as a “clock”
•some isotopes are naturally unstable which causes them to emit radiation as they radioactively decay
•each isotope decays at a characteristic and unchangeable rate called its half-life
•Half-life: time it take for half of the atoms in a sample of a radioactive substance to decay
•If an isotope’s half-life is 1 year, 50% of the radioactive atoms will have decayed in a year. In
another year, 25% will decay, and so on
13.3 Biogeography Considers Species’ Geographical Locations
•Biogeography: study of distribution of species across the planet
A. The Theory of Plate Tectonics Explains Earth’s shifting Continents
•Plate tectonic: theory that Earth’s surface consists of several rigid layers, called tectonic plates, that
move in response to forces acting deep within the planet
•in some place where plates come together, one plate dives beneath another, forming a deep trench
•other areas consist of mountain ranges forming as the plates become wrinkled and distorted
•molten rock seeps to Earth’s surface and forms new plate material where plates move apart
B. Species Distributions Reveal Evolutionary Events
•Biogeography provides insight into large- and small-scale evolutionary events
13.4 Anatomical Comparisons May Reveal Common Descent
A. Homologous Structures Have a Shared Evolutionary Origin
•Two structures are termed homologous if the similarities between them reflect common ancestry
•homologous structures share a common evolutionary origin but may not have the same function
B. Vestigial Structures Have Lost Their Functions
•Vestigial structure has no apparent function in one species, yet is homologous to a functional organ in
another
•humans have several vestigial organs; the tiny muscles that make hairs stand on end help our furry
ancestors conserve heat or show aggression, but in us, they serve only as the basis of goose bumps
C. Convergent Evolution Produces Superficial Similarities
•Analogous structures are anatomical parts that evolved independently
find more resources at oneclass.com
find more resources at oneclass.com
