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Geologic Time Study Guide ­The Earth was formed about _4
.6 billion _________________ years ago. ­All of the _p
lanets ___ in the solar system and the _s un _____ were formed at the same time. The planets and the sun _a
ccreted __ (came together) in a _ solar nebula ________, a cloud of gas and dust. _ Gravity _____ caused bits of rock and metal in space to come together and smash into each other until they got larger and larger and formed _ planets ____. ­When Earth first formed it was very hot for three main reasons. First, _g
ravitational contraction ____ created a lot of pressure in interior of the planet as the rock and metal came together. Secondly, _ radioactive decay ____ of unstable elements with short half lives produced heat in the interior of the Earth as they stabilized. Finally, _ bombardment __ of asteroids during the first 500 millions years of Earth’s life produced much heat. When the interior of the Earth was still so hot that it was entirely molten, _g
ravity ___ caused the more dense elements to draw into the interior, and the less dense elements rose toward the surface. This division of the Earth into layers based on density is called _ differentiation ______. ­The Earth produces its own internal heat. _R
adioactive decay ______ of elements in the interior of the Earth produce heat, and _c onvection ________ in the Earth’s mantle moves it from the interior of the Earth to the surface. ­Scientists have used _ absolute ______ dating methods like radiometric dating to date _ rocks __ from the Earth’s crust as well as _m
oon rocks __ and _ meteorites _____ that formed at the same time as Earth to help determine the age of the Earth. They also used relative dating methods and _f ossils _____ to help determine Earth’s _ history ____________. ­The _g
eologic time scale ______ is the division of Earth’s history into blocks of time based on major events in _g
eology _______, _ climate ________, and the _ evolution ____ of life. Major events that divide the blocks on the time scale include mass _e
xtinctions __ and other disappearances of _s pecies of life ______ from the _ fossil _____ record. ­The geologic time scale is divided into segments. The largest segments are called _ eons __, which are then broken into _ eras ____, which are further divided into _ periods ____, which can be divided into _ epochs _____ or simply subdivided into early, middle, and late sections. ­We currently live in the _ Phanerozoic ____ eon, in the _ Cenozoic _____era, in the _ Quarternary __ period, and in the _ Holocene ___ epoch. ­Humans have only been around for about _ 200,000 __________ years. ­Put the following eons in order from earliest to current: Archean, Phanerozoic, Hadean, Proterozoic. Hadean, Archean, Proterozoic, Phanerozoic ­Put the following eras in order from earliest to current: Precambrian, Cenozoic, Paleozoic, Mesozoic. Precambrian, Paleozoic, Mesozoic, Cenozoic ­Put the following periods in order from earliest to current: Cretaceous, Ordovician, Carboniferous (Pennsylvanian and Mississippian), Triassic, Quaternary, Cambrian, Permian, Jurassic, Silurian, Tertiary, Devonian. Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Mississippian and Pennsylvanian), Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary The longest era is the _P
recambrian ___. The shortest era is the _ Cenozoic ________. The extinction of dinosaurs made it possible for _h
umans _________ to flourish on Earth. This is clear from the _ fossil record ____. Below, list the periods of the geologic time scale in order from most recent to earliest, and list one or two major events from each period beside it. Phanerozoic
Quaternary: “Age of man, ”human civilization, first homo sapiens, mammoths, “Visible Life”
“Age of Mammals”
mastodons, mass extinction, last ice age Tertiary: first hominids, first large mammals and primitive primates (modern whales, horses, dogs, bears, modern birds, monkeys, deer, cats, pigs, rodents), grasses Mesozoic
Cretaceous: much tectonic and volcanic “Age of Reptiles”
activity, primitive marsupials, many dinosaurs, feathered dinosaurs, butterflies, ants, , snakes, bees; modern continents, mass extinction (K­T extinction) killed dinosaurs, 50% of marine invertebrates Jurassic: many dinosaurs, sauropods, first birds, first flowering plants, many fern, ginkgos, conifers Triassic: first dinosaurs, first mammals, first true flies, many mollusks, many reptiles, minor extinction made way for many dinosaurs Paleozoic
Proterozoic Perman: “Age of Amphibians,” reptiles and amphibians dominant, Pangaea, modern oxygen levels in atmosphere, first stoneflies, bugs, beetles; largest mass extinction kills trilobites, 50% of animal families, 95% of marine life, and many trees Carboniferous: coal swamps, corals, brachiopods, amphibians common Pennsylvanian: first mayflies, cockroaches, and reptiles; many ferns Mississippian: first winged insects Devonian: “Age of the fishes,” many fish and land plants, first tetrapods, amphibians, sharks, bony fish; many coral reefs, brachiopods, and crinoids, new insects; mass extinction killed 30% of animal families Silurian: first jawed fish, millipedes, centipedes, first vascular land plants; high seas worldwide Ordovician: primitive land plants, primitive fish, seaweed, and fungi; first corals; high seas, global cooling Cambrian: “Cambrian explosion” of life; “Age of Trilobites”; many marine invertebrates ­ shellfish, trilobites, brachiopods, mollusks; first vertebrates, earliest primitive fish; Rodinia breaks up; mass extinction kills 50% of animal families Vendian/Ediacaran: first multicelled organisms, sponges, algae, soft­bodied invertebrates, oxygen buildup, Archeozoic (Archean)
formation of Rodinia, mass extinction “Ancient Life” ­ first single celled organisms, blue­green algae, bacteria, first oxygen released in atmosphere due to bacteria “Rockless eon” ­ solidifying of Earth’s oceanic and continental crust