Spare Parts by Carol Ann Rinzler

Author:Carol Ann Rinzler
Language: eng
Format: epub
Publisher: Skyhorse Publishing
Published: 2017-03-03T05:00:00+00:00

HOW OLD IS YOUR EON?12

Geologists measure the age of the earth in Eons, which are subdivided into Eras, which are subdivided into Periods and then Epochs and finally Ages. The names of these time spans come from the Greek, as you can tell as soon as you see -zoic from the Greek word zoion meaning animal tacked on to the end. For example, add -zoic to the Greek phaneros meaning visible and you get the Phanerozoic Eon, the “time of visible animals,” which is to say, the time of us. And so on.

This list shows the geologic time scale, a scheme invented by British geologists to measure the earth’s time periods. In 1841, John Phillips published the first such chart, standardizing earth’s history based on the types of fossils found in each era.13 It begins at the top with the latest, our current moment of supremacy, and then goes backwards all the way to the Hadean Era, the chaotic flash in the universe when the earth was formed. The common Greek prefixes cen- from kainos, meso- and paleo- translate to late, middle and early; eo- means earliest, i.e., dawn, and neo- means new. As for the rest of the names here, the truly curious may wish to check out their fuller meaning and history in the wonderfully expansive Online Etymology Dictionary at http://etymonline.com/, which tells such linguistic tales as this: “Cambrian (adj.) 1650s. ‘from or of Wales or the Welsh,’ from Cambria, variant of Cumbria, Latinized derivation of Cymry, the name of the Welsh for themselves, from Old Celtic Combroges ‘compatriots.’ Geological sense (of rocks first studied in Wales and Cumberland) is from 1836.”

The Phanerozoic Eon (542 million years ago to the present)

The Cenozoic Era (63 million years ago to now), the time of “new” or “recent” animals, including us, comprises the current Quaternary Period and the preceding Neogene and Paleogene Periods, when mammals and man rose to dominate life on earth.

The Mesozoic Era (251 to 65 million years ago), the time of the “middle animals,” a name coined by Phillips in 1840, includes the Cretaceous, Jurassic, and Triassic Periods when mammals and birds appeared and then poof! the moment approximately 100 to 116 million years ago when all the birds on earth, descendants of well-toothed carnivorous dinosaurs, somehow evolved to lose the genes required for building teeth. The birds’ greatest achievement, however, was their surviving the mass extinction of all nonavian dinosaurs 65 million years ago, the catastrophic event that opened the door for the rise of the eventually-dominant mammals, most of whom would come to live on the continents just beginning to drift apart from their original configuration.

The Paleozoic Era (542 to 251 million years ago), the time of “ancient animals,” includes the Permian, Carboniferous, Devonian, Silurian, Ordovician, and Cambrian Periods when marine vertebrates—fish, seabirds, sea reptiles and sea-going mammals—were the prevailing life forms. Midway through this era, just short of 400 million years ago, the first four-limbed vertebrates, creatures who looked like lizards but were actually the ancestors of all mammals, shuffled out of the waters to live on land.

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