1. History of the earth
Ch. 9 – earth science

2. Ch. 9.1 - Divisions of Geologic Time
Marked by major changes to Earth’s surface, climate, and types of organisms.
Geologic Time Scale (Table 1, p.231 Earth Text)
Ma = mega-annum = million years

3. Eons and Eras
a. Eon – Largest unit of geologic time (4)
Hadean Eon
Archean Eon all three belong to Precambrian
Proterozoic Eon
Phanerozoic Eon – This Eon is divided into smaller units of time called Eras.
Paleozoic Era
Mesozoic Era
Cenozoic Era

4. 3. Periods and Epochs
Most Eras are divided into Periods
Periods are divided into Epochs
Epochs can be divided into ages
4. Sequence:
Eon – Era – Period - Epoch

5. Ch. 9.2 - Precambrian Time and the Paleozoic Era
Evolution: The gradual development of new organisms from preexisting organisms (or: change of organisms over time)
Evolution occurs by means of natural selection.
Evidence for evolution includes the similarity in skeletal structures of animals.
The theory of evolution was proposed by Charles Darwin in 1859.

7. Proportional Geologic Time Scale Approximately how many billion years did the Precambrian period last? _______ What percentage of time since Earth was formed about 4.6 billion years ago was in the Precambrian period? _______________