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Life on Earth

Ch8 Test: Geologic Time Scale

Earth’s history is recorded on a time line called the ___ ___ ___. geologic time scale
Paleontologists divide units of time using __ __ selected by certain criteria. index fossils
Index fossils must have ___ ___, so they are preserved easily. hard parts
Index Fossils must be geographically ____, so they are easily found widespread
Index fossils must have lived in many ____, so as to be preserved in many rock types. environments
Index fossils must become ____ after a short period, so that small units can be established. extinct
The divisions of the geologic time scale are eons, eras, periods, and ____ epochs
___ are the largest divisions and represent the longest time periods Eons
The Phanerozoic Eon is divided into three ____: Paleozoic, Mesozoic, and Cenozoic eras
The Cenozoic Era is divided into the Paleogene, Neogene, and Quaternary _____. periods
A ___ ___ is the dying off of many different species during a short geologic time period. mass extinction
___ percent of all species that ever lived are now extinct Ninety-nine
Mass extinctions can happen over a period of several ___ years million
A ___ ___ causes a drastic change in the numbers of organisms over a short period of time. catastrophic event
There is evidence that ___ ___(global warming or cooling) has caused some mass extinctions, including those ending the Devonian and Ordovician periods. climate change
Global warming is linked to ___ ___, such as carbon dioxide, in the atmosphere greenhouse gases
___ ___ can cause can cause oxygen levels in water to decrease and sea levels torise. Global warming
___ ___ could lower sea levels and decrease warm, shallow-water environments Global cooling
___ can contribute to mass extinctions by emitting dust, ash, lava, and gases that can affect climate and organisms Volcanoes
The 1902 eruption of Mt. Pelee produced a cloud of dust and gas that caused worldwide___. cooling
The mass extinction ending the ___ period is attributed to volcanic eruption Cretaceous
___ ___, including the Siberian and Deccan Traps, may have caused mass extinctions Basalt flows
___ ___ can cause climate change by blocking the Sun’s rays Volcanic haze
An ___ impact is thought to have contributed to the Cretaceous mass extinction asteroid
The impact could shroud the Earth in sun-blocking dust and haze, lowering temperaturesand inhibiting ___. photosynthesis
___ time represents 88 percent of Earth’s history Precambrian
___ in adjacent rock layers are more similar than fossils in widely separated layers Fossils
The more ___ a fossil was formed, the more it resembles a living organism recently
Precambrian time is divided into three ___: Hadean, Archean, and Proterozoic eons
Most Precambrian rock is ___, so it is more difficult to date. metamorphosed
Precambrian atmosphere had very little ___ and no ozone layer oxygen
Ancient ___ contain fossils of Earth’s earliest known organisms stromatolites
Stromatolites are composed of alternating layers of sediments and ___ cyanobacteria
___ are single-celled,photosynthetic blue-green algae Cyanobacteria
Cyanobacteria released ___ into the atmosphere through photosynthesis oxygen
___ ___ began to favor organisms that used oxygen Natural selection
An ___ ___ developed to shield Earth from ultraviolet rays ozone layer
More complex, soft-bodied organisms, called ___ ___, evolved Ediacaran fauna
Organisms with hard parts evolved during the ___ Era Paleozoic
During the ___ explosion, shelled animals and other invertebrates greatly increased in number and diversity. Cambrian
___ were the most commonly fossilized organisms of the Cambrian Period Trilobites
Invertebrates, such as corals and brachiopods, evolved, as did ___ insects
Vertebrates evolved during the ___ Era, many of which lived in oceans Paleozoic
One group of bony fish evolved into modern fish; the other evolved into ___ amphibians
___, which lay watertight eggs, allowed organisms to spread into drier habitats Amniotes
Plants developed ___ systems, allowing them to spread onto land vascular
___ ___, ferns, and pine trees appeared during the Mississippian and PennsylvanianPeriods Club mosses
Club mosses, ferns, and pine trees became large ___ deposits used as an energy resource today coal
___ ___ occurred during the Ordovician, Devonian, and Permian Periods Mass extinctions
The late ___ extinction ended the Paleozoic era, with the extinction of 90 percent of marine species and 70 percent of land pecies. Permian
Two causes of the Permian extinction are the uplifting of ___ and the emission of ash and sulfur from theSiberian Traps. Pangaea
The ___ Era includes the Triassic, Jurassic, and Cretaceous Periods Mesozoic
Algae, ___, stromatolite organisms, and reef-building corals evolved during the Mesozoic Era clams
Ocean vertebrates included predatory reptiles; land vertebrates included frogs, crocodiles, ___, and dinosaurs pterosaurs
___ evolved from small to larger species, including the Apatosaurus Dinosaurs
Scientists originally thought dinosaurs were ___-___, but they now believe dinosaurs’structures were more similar to those of mammals and birds cold-blooded
Dinosaurs became ___ at the end of the Cretaceous Period extinct
___ was a dinosaurlike animal believed to be an ancestor of birds Archaeopteryx
___ evolved in the Triassic Period alongside the dinosaurs Mammals
As dinosaurs became extinct, mammals moved into their ___ niches
___, plants with seeds but no flowers, dominated the Mesozoic Era Gymnosperms
___, flowering plants, appeared near the end of the Mesozoic Era Angiosperms
Mass extinctions occurred at the end of the ___, Jurassic, and Cretaceous Periods Triassic
The current era, the ___, is divided into seven epochs Cenozoic
Modern mammals, including modern whales and ___, evolved primates
Primates have opposable ___ and two eyes that look forward thumbs
About 4.4 million years ago, the ___, the group that includes homo sapiens, evolved hominids
___ plants increased and diversified into the more than 250,000 species that exist today Flowering
Extinctions in the Cenozoic Era have occurred by natural selection and due to ___ causes human
Created by: jnosik