Geologic Time Scale

Chapter 2, Section 3 – Unit AScience 8Messana

1. Hadean 2. Archean 3. Proterozoic 4. Phanerozoic

#1-3 make up Precambrian Time

Eons -> Eras -> Periods -> Epochs

Change in name is due major geologic or climatic events!!

90% of Earth’s history Lasted nearly 4 billion years of Earth’s

4.6 billion years Volcanic ash & dust ->clouds formed -

>rain Single-celled micro-organisms in ocean at

end No animals! No plants!

544 million years ago – present Explosion of Life! 3 Eras:

◦ Paleozoic Era – “Age of Amphibians”

◦ Mesozoic Era – “Age of Dinosaurs”

◦ Cenozoic Era – “Age of Mammals”

544 mya – 248 mya All life in ocean until end Fish developed Reptiles, Insects, Ferns developed – moving

life onto land at end Ends with a Mass Extinction (from a

meteor strike?)– kills 90% of all ocean species

248 mya – 65 mya Dinosaurs rule! Small mammals, birds, flowering plants Ends with Mass Extinction due to meteor

strike off Mexico ->dust cloud blocked sunlight, killed plant life and affected food chain

65 mya – Present

Large warm-blooded mammals, modern birds, flowering plants

Animals developed migration techniques Tertiary Period Quaternary Period = last 2 million yrs

◦ Ice ages

◦ 1st modern human fossils = 100,000 yrs old◦ Humans are 7 seconds of 12 hour clock!!

Earth is constantly changing due to the same basic forces

EX: Slow = erosion, plate movement

Fast = volcano, earthquake