GEOCHRONOLOGIC The geologic time is divided into a number of of differing sizes. From the largest units to the smaller units, they are: > Eras > Periods > Epochs •Eons units are geochronologic units or time units. THE MODERN GEOLOGICAL TIME SCALE Word modifiers: - before pro - evidence phanero - ancient paleo middle – meso new – neo resent – ceno dawn – eo - life zoon FIGURE 3-1 Geologic Time Scale. EONS In order from oldest to youngest: Eon—This is an informal time unit referring to the earliest history where no rock record has been preserved. Hadean Eon—"ancient or archaic“—oldest rocks on Earth (~4 billion to 2.5 billion years ago) Archean Eon—"beginning life" (2.5 billion to 542 million years ago) Proterozoic Eon—"visible life" (542 million years ago to present) Phanerozoic PRECAMBRIAN The Archean and Proterozoic are together referred to as the Precambrian, meaning "before the Cambrian Period." The Precambrian encompasses 87% of geologic history.
GEOCHRONOLOGIC The geologic time is divided into a number of of differing sizes. From the largest units to the smaller units, they are: •Eons > Eras > Periods > Epochs units are geochronologic units or time units. THE MODERN GEOLOGICAL TIME SCALE Word modifiers: pro - before phanero - evidence paleo - ancient meso – middle neo – new ceno – resent eo – dawn zoon - life FIGURE 3-1 Geologic Time Scale. EONS In order from oldest to youngest: Hadean Eon—This is an informal time unit referring to the earliest history where no rock record has been preserved. Archean Eon—"ancient or archaic“—oldest rocks on Earth (~4 billion to 2.5 billion years ago) Proterozoic Eon—"beginning life" (2.5 billion to 542 million years ago) Phanerozoic Eon—"visible life" (542 million years ago to present) PRECAMBRIAN The Archean and Proterozoic are together referred to as the Precambrian, meaning "before the Cambrian Period." The Precambrian encompasses 87% of geologic history.
Ch03%20Time%20and%20Geology%20Notes.docx