Cambrian: Geologic period that begins the Paleozoic Era 570 million years ago. Marked in its beginning by a proliferation of animals with hard, preservable parts, such as brachiopods, trilobites, and . . . View Full Definition
Precambrian: Informal term describing 7/8 of geologic time from the beginning of the earth to the beginning of the Cambrian Period of the Paleozoic Era. During this time the atmosphere and oceans formed, . . . View Full Definition
Basement: The oldest rocks recognized in a given area, a complex of metamorphic and igneous rocks that underlies all the sedimentary formations. Usually Precambrian or Paleozoic in age.
Radiolarian: A group of one-celled marine animals with a siliceous skeleton that occupies shallow portions of the water column. Radiolarians have a range from Cambrian to present.
Trilobites: A group of benthonic, detritus-feeding, extinct marine invertebrate animals (phylum Arthropoda), having skeletons of an organic compound called chitin. Trilobites appear in abundance early i . . . View Full Definition
Era: A subdivision of geologic time that is longer than a period but shorter than an eon. Precambrian, Paleozoic, Mesozoic, and Cenozoic are the eras of the time scale from oldest to youngest.
Rodinia: Name applied to the precambrian supercontinent.
Laurentia: Name applied to the core of North America in the times from the breakup of the precambrian supercontinent Rodinia to the formation of Pangaea.
Ordovician Period: Geologic period of the Paleozoic Era after the Cambrian Period between 500 and 435 million years ago. Major advances during this period include the bony fish and possibly land plants (during . . . View Full Definition
Paleozoic Era: The period of time beginning 570 million years ago ending 245 million years ago; falls between the Proterozoic and Mesozoic Eras and is divided into the Cambrian, Ordovician, Silurian, Devon . . . View Full Definition
Word of the Day:
Fragrance: The sensation of the gases released from ground coffee as they are inhaled through the nose. Ranges from sweetly floral to sweetly spicy.