History GenbioG

• Traces or imprints of once-living things

  Fossils
• dead organism covered by layer of sediment which presses together to form what kind of rock?

  sedimentary rock
• layers where the fossils are found tells a scientist the what age?

  relative age
• Estimating age of fossils by its position in the rock layers

  relative dating
• when a scientist want to determine the age of fossils more precisely

  absolute dating
• method of measuring object by years

  absolute dating
• scientist examines ______ , which overtime decay by releasing energy

  atoms
• the time it takes for a half a sample of atoms to decay

  half-life
• scientist measure the ratio of stable to unstable atoms to determine the age of a sample rock
• the standard method used to divide the earths long natural history into manageable parts

  geologic time scale
• divided into eras which are characterize by the type of organism that dominated the earth at that tim
• precambrian time is the formation of earth 4.6 billion years ago to about 544 millions years ago
• precambrian time have volcanic eruptions, meteorites , intense radiation from the sun
• early atmosphere had no oxygen
• first organism were prokaryotes without nucleus
• cynobacteria appeared and produced own food and released oxygen
• ozone layer forms in upper atmosphere and absorbs radiation from the sun
• paleozoic era is rocks rich in fossils of animals such as sponges, corals, clam, squid, and trilobites
• mesozoic era is dominated by dinasaurs and other reptiles
• cenozoic era is sometimes called the aged of mammals
• cenozoic era include some periods known as ice age
• most scientist think that dinasaurs happened because of extreme changes in the climate of the earth
• german scientist alfred wegener noticed that the continents of earth look likes puzzle pieces
• pangea a proposed long ago continents formed one landmass surrounded by gigantic ocean
• pangea means all earth
• mid 1960 tuzo wilson came up with the idea that continents were not moving by themselves
• wilson thought that huge pieces of earth crust were pushed by forces within the planet
• each piece of crust is called the tectonic plates
• wilson's theory of how the huge pieces of crust move is called plate tectonics
• outer crust of earth is broken into seven large plates and several smaller ones
• motion of the plates causes continents to move