| A | B |
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| Geologic time scale. | division of Earth's history into time units based largely on the types of life-forms that live only certain periods. |
| Eons. | longest subdivision in the geologic time scale that is based on the abundance of certain types of fossils . |
| Eras. | second-longest division of geological time; is subdivided into periods and is based on major worldwide changes in types of fossils. |
| Periods. | horizontal row of elements in the periodic table whose properties change gradually and predictably. |
| Epochs. | next-smaller division of geological time after the period; is characterized by differences in life-forms that may vary regionally. |
| Organic evolution. | change of organisms over geologic time. |
| Species. | group of organisms that reproduces only with other members of their own group. |
| Natural selection. | process by which organisms that are suited to a particular environment are better able to survive and reproduce than organisms that are not. |
| Trilobite. | organism with a three-lobed exoskeleton that was abundant in Pleozoic oceans and is considered to be an index fossil. |
| Pangaea. | large, ancient landmasss that was composed of all the continents joined together. |
| Precambrian time. | longest part of Earth's history, lasting from 4.0 billion to about 544 million years ago. |
| Cyanobacteria. | chlorophyll-containing, photosynthetic bacteria thought to be one of Earth's earliest life-forms. |
| 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. |
| How many millions of years ago did the era in which you live begin? | 65 million. |
| During what period did the most recent ice age occur? | Quaternary. |
| What is the next smaller division of geologic time after the era? | the period is the next smaller. |
| Name a fossil older than a tyranosaurus rex bone and a trilobite. | Stromatolite. |
| During which era did the dinosaurs live? | Mesozoic. |
| Which type of plant has seeds without protective coverings? | Gymnosperms. |
| Which group of plants evolved during the Mesozoic Era and is dominant today? | Angiosperms. |
| In which era did the Ediacaran fauna live? | They lived in the Precambrian period. |
| Infer why plants couldn't move onto land until an ozone layer formed. | Too much harmful ultraviolet radiation from the Sun reached Earth's surface. |
| Explain why trilobites are classified as index fossils. | They were widespread, and individual species existed for a limited amount of time before becoming extinct. |
| Compare and contrast the most significant difference between Precambrian life-forms and Paleozoic life-forms. | Most organisms of Precambrian age lacked the hard parts that developed in the Paleozoic Era. |
| Describe how natural selection is related to organic evolution. | It occurs through natural selection, which is the process by which organisms with characteristics best suited to their environment survive and reproduce. |
| Why is the old proposition that giraffe necks gradually lengthened by stretching a false theory? | Acquired traits are not hereditary. |
| Suggest some reasons why trilobites might have become extinct at the end of the Paleozoic Era. | Plate tectonic processes that changed the make up of the land and seas, disappearing of shallow seas where they lived, meteroite impact. |
| A student found what she thought was a piece of dinosaur bone in Pleistocene sediment. How likely is it that she is right? | It is not likely because dinosaurs became extinct long before the Pleistocene Epoch. |
| Why didn't mammals become dominant until after the dinosaurs disappeared. | Dinosaurs were better-adapted to the habitat until they became extinct. Mammals were then the best-adapted. |
| Fossils. | remains, traces or imprints of prehistoric organisms. |
| Life. | state of being in which one grows,reproduces and maintains a constant internal environment. |
| Dinosaur. | a reptile from one of two orders that dominated the Mesozoic Era. |
