. Adventures with animals and plants. Biology. 534 Era 7 Psychozoic Era 6 Cenozoic Era 5 Mesozoic Era 4 Paleozoic The Earth mid Its inhabitajits Change uni r x Began about 1,000,000 years ago Began about 550,000,000 years ago. Began about 1,200,000,000 years ago Began about 2,000,000,000 years ago Began about 3,000,000,000 years ago Fig. 483 (above) A diagram of the 7 eras of time. Read from the bottom up. The rocks of the first era were the first to be laid down OJid are generally deepest down in the earth. Note that about five sixths of the eartlfs his- tory was over when the fourth {Paleozo
. Adventures with animals and plants. Biology. 534 Era 7 Psychozoic Era 6 Cenozoic Era 5 Mesozoic Era 4 Paleozoic The Earth mid Its inhabitajits Change uni r x Began about 1,000,000 years ago Began about 550,000,000 years ago. Began about 1,200,000,000 years ago Began about 2,000,000,000 years ago Began about 3,000,000,000 years ago Fig. 483 (above) A diagram of the 7 eras of time. Read from the bottom up. The rocks of the first era were the first to be laid down OJid are generally deepest down in the earth. Note that about five sixths of the eartlfs his- tory was over when the fourth {Paleozoic) era be- gan. But that was scarcely recent. It was ^^0,000,000 years ago! Fig. 484 (left) After long years of careftd study of the rocks, geologists think this ?nap represents North America during an early pe- riod of the Paleozoic era. Seas are shown in white. Was yotir ho7netown loca- tion under or out of water at this time? The earth in the first three eras. The first rocks, it is estimated, were formed three billion (3,000,000,000) years ago as the earth cooled. Geologists think it probable that no life existed during the first billion years, the first era (Azoic). After about a billion years great changes occurred that have left their mark on the eaith. Geologists therefore say that a second era began. In the rocks laid down. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kroeber, Elsbeth, 1882-; Wolff, Walter Harold, 1901-. Boston : D. C. Heath
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Keywords: ., bookcentury1900, bookpublisherbostondcheath, booksubjectbiology
