Railsback's Some Fundamentals of Mineralogy and Geochemistry The standard geologic scale MYBP (millions of MYBP (millions of years MYBP before present) Era PeriodEpoch Eon Era Period before present) 0 Beginning 0 0 of present 0.01 interglacial Major 2.6 phase NARY

65 QUATER- ERO- 23 2.6 First major ZOIC 251 events CENO- Northern 65 Hemisphere PALEOZOIC 5 glaciation PHAN ZOIC 0.54 billion years ago 542 *

(age of 's oldest easily NEOGENE 23 recognized ) 145 CENOZOIC

TERTIARY First cooling 34 from Cretaceous-

Mesoproterozoic MESOZOIC 200 56 to-Eocene warm period PALEOGENE "Great 65 Oxidation 251 The attempts to Event" give names to meaningful periods of 2.5 billion years ago 299 time in Earth , just as scholars of (an arbitrary numerological 2500 American history speak of a "colonial boundary) 318 period", an "antebellum period", and so on. Note the decreasing size of time Late 359 periods closer to the present (i.e., to the top of diagram). We live in the most recent days of the Holocene Middle Archean of the Quaternary Period of the

PRECAMBRIAN 416 Cenozoic Era of the Eon.

ARCHEAN Early Archean 444 *In the first decade of the 21st , the International Commission on 3.8 billion years ago PALEOZOIC divided the Cenozoic period (more or less age of Earth's 3800 previously known as "the " into oldest surviving rocks) 488 "Paleogene" and "Neogene". Much literature still uses the word "Tertiary" (Hadean time is included within the and the letter "T" as its abbreviation. Archean by many geologists.) Many Earth scientists also continue to 542 refer to the boundary at the end of the Millions of HADEAN 4.6 billion years ago Cretaceous as the "K-T" boundary, even years before though it would be the "K-P" boundary in (age of Earth) 4600 Millions of years present the new usage. before present

After Stanley's Earth History (3rd edn 2009) LBR Stanley11aLS 8/1999; rev 10/2010