History of the earth Ch. 9 – earth science

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

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

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

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.

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? _______________