Part 2

1.0 = One million years ------------+-----------------+---------------+-------------------- | | TIME SCALE | ERAS | PERIODS |(After Barrell)| CHARACTERISTIC | +-------+-------+ LIFE | |Minimum|Maximum| ------------------------------+-------+-------+-------------------- PSYCHOZOIC | Recent | | | ------------+-----------------+ 1 | 1.5 | AGE OF MAN | Pleistocene | | | +-----------------+-------+-------+-------------------- | Pliocene | 7 | 9 | +-----------------+-------+-------+ CENOZOIC | Miocene | 19 | 23 | AGE OF MAMMALS +-----------------+-------+-------+ AND MODERN | Oligocene | 35 | 39 | FLOWERING PLANTS +-----------------+-------+-------+ | Eocene | 55 | 65 | ------------+-----------------+-------+-------+-------------------- | Cretaceous | 95 | 115 | +-----------------+-------+-------+ | Comanchian | 120 | 150 | MESOZOIC +-----------------+-------+-------+ AGE OF REPTILES | Jurassic | 155 | 195 | +-----------------+-------+-------+ | Triassic | 190 | 240 | ------------+-----------------+-------+-------+-------------------- | Permian | 215 | 280 | AGE OF AMPHIBIANS +-----------------+-------+-------+ AND | Pennsylvanian | 250 | 330 | ANCIENT FLORAS +-----------------+-------+-------+-------------------- | Mississippian | 300 | 370 | +-----------------+-------+-------+ AGE OF FISHES PALEOZOIC | Devonian | 350 | 420 | +-----------------+-------+-------+-------------------- | Silurian | 390 | 460 | +-----------------+-------+-------+ AGE OF HIGHER | Ordovician | 480 | 590 | SHELLED +-----------------+-------+-------+ INVERTEBRATES | Cambrian | 550 | 700 | ------------+-----------------+-------+-------+-------------------- | | | PROTEROZOIC | | 925 | AGE OF PRIMITIVE | | | INVERTEBRATES ------------+ Systematic +---------------+-------------------- | classification | LONG EROSIONAL INTERVAL ------------+ variable +---------------+-------------------- | | | DAWN OF UNICELLULAR ARCHEOZOIC | | 1500 | LIFE, ALGAL FORMS | | | REPORTED ------------+-----------------+---------------+--------------------

BIBLIOGRAPHY

BARRELL, J.—Rhythms and Measurements of Geological Time. Bull. Geol. Soc. Am., Vol. 28, 1917, pp. 745-904.

BECKER, GEO. E.—The Age of the Earth. Smithsonian Misc. Coll., LVI., No. 6, 1910.

CHAMBERLAIN, T. C.—Diastrophism and the Formative Processes, XIII. The Time over which the Ingathering of the Planetesimals was Spread. Jour. Geol., Vol. XXVIII, 1920, pp. 675-81.

HARKER, A.—Geology in relation to the exact sciences, with an excursus on geological time. Nature, Vol. 95, 1915, pp. 105-109.

HOLMES, A.—The Age of the Earth. Harper and Bros., London and New York, 1913.

JOLY, J.—Radioactivity and Geology. Van Nostrand, N. Y., 1909;

An Estimate of the Geological Age of the Earth. Trans. Roy. Soc. Dublin, VII. 1899, pp. 23-66;

The Age of the Earth. Phil. Mag., 6th ser., Vol. XXII, 1911, pp. 359-80.

SOLLAS, W. J.—Presidential Address. Quart. Journ. Geol. Soc., Vol. 65, 1909, pp. cxii; Proc. Geol. Soc. of London, Sess. 1908-9, pp. i-cxxii.

WALCOTT, C. D.—Geologic Time, as indicated by the sedimentary rocks of North America. Smithsonian Rep. 1893, pp. 301-334; Jour. Geol. Vol. III, 1893, pp. 639-674.

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