science vocab 4-2-08
Terms
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- fossil
- remains, imprints, or traces of prehistoric organisms that can tell when and where organisms once lived and how they lived
- cyanobacteria
- chlorophyl containing, photosynthetic bacteria thought to be one of the worlds earliest life forms
- mesozoic era
- middle era of earth's history, during which Pangaea broke apart, dinosaurs appeared, and reptiles and gymnosperms were the dominant land life forms
- principle of superposition
- states that older rocks are at the bottom and younger rocks are at the top
- unconformity
- gap in the rock layer that is due to erosion or periods without any depostion
- epoch
- the next smaller division of geologic time after the period; characterized by differences in life forms that might vary regionally
- index fossil
- remains of species that existed on earth for a reletively short period of time, they were abundant and widespread geographically, and can be used by geologists to assign the ages of rock layers
- permineralized remains
- fossils in which the spaces inside are filled with minerals from groundwater
- cenozoic era
- era of recent life that began about 65 million years ago and continues today; includes the first apperance of homo sapiens about 400 thousand years ago
- precambrian time
- longest pert in earth's history, lasting from 4 billion to about 544 million years ago
- uniformitarianism
- principle stating that earth processes occuring today are similar to those in the past
- paleozoic era
- era of ancient life, which began about 544 million years ago when organisms developed hard parts and ended with mass extinctions about 245 million years ago
- organic evolution
- change of organisms over geologic time
- pangea
- large, ancient landmass that was composed of all continents joined together
- period
- horizontal rows of elements in the periodic table whose properties change gradually and predictably
- eon
- longest subdevision in geologic timescale; based on the abundance of certain types of fossils and subdevided into eras, periods and epochs
- trilobite
- organism with a three lobed skeleton that was abundant in Paleozoic oceans and is considered to be an index fossil
- species
- group of organisms that reproduce only with other members of their own group
- natural selection
- process by which organisms that are suited to a particular environment are better to survive and reproduce than organisms that are not
- half-life
- the time it takes for half the atoms of radioactive isotope to decay
- radioactive decay
- process in which some isotopes break down into other istotopes, releasing energy and particles from the nucleus
- carbon film
- thin film of carbon residue produced as a fossil
- radiometric dating
- process used to calculate the absolute age of rock by measuring the ratio of parent isotope to daughter product in a mineral and knowing the half- life of the parent
- absolute age
- age of rock- determined by using properties of the atoms that make up materials
- cast
- a type of body fossil that forms when crystals fill a mold or sediments wash into a mold and harden into rock
- geologic time scale
- division of earth's history into time units based largely on the types of life forms that lived only during certain periods
- mold
- a type of body fossil that forms a rock when an organism with hard parts is buried, decays or dissolves, and leaves a cavity in the rock
- relative age
- the age of something compared with other things