Geologic Time Scale

Question 1

Hadean Eon

Answer 1

4. 6 - 3.85 BYA
   - formation of the earth
   - origin of life

Question 2

Archean Eon

Answer 2

3. 85-2.5 BYA
   - evolution of prokaryotes
   - first photosynthetic bacteria
   - O2 starts to accumulate in atmosphere
   - origin of aerobic respiration

Question 3

Proterozoic Eon

Answer 3

2. 5 billion - 542 million years ago
   - high levels of O2 in the atmosphere
   - origin of eukaryotic cells
   - evolution & diversification of protists, fungi, and early animals

Question 4

Phanerozoic Eon

Answer 4

542 MYA - present day

- all eras and periods

Question 5

Paleozoic Era

Answer 5

542 MYA - 251 MYA

- Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods

Question 6

Cambrian Period

Answer 6

• Appearance of modern animal phyla

- Appearance of first vertebrate animals

Question 7

Ordovician Period

Answer 7

• Major radiations of marine invertebrate animals and jawless fishes
• Mass extinction at end of period

Question 8

Silurian Period

Answer 8

• first jawed fish
• first arthropods
• first vascular land plants

Question 9

Devonian Period

Answer 9

• Vascular land plants diversify
• First amphibians
• First insects
• First seed producing plants
• Mass extinction at end of period

Question 10

Carboniferous Period

Answer 10

• Vascular plants in large swamp forests (eventually formed coal deposits)
• Amphibians diversify
• First reptiles

Question 11

Permian Period

Answer 11

• Insects & reptiles abundant on land in swamp forests
• Fishes colonize freshwater
• Continents coalesce into Pangaea
• Mass extinction at end of period

Question 12

Mesozoic Era

Answer 12

251-65.5 MYA

- Triassic, Jurassic, Cretaceous

Question 13

Triassic Period

Answer 13

• Gymnosperms dominant land plants
• Reptiles dominant land animals
• Radiation of dinosaurs
• First mammals
• Pangaea begins to break apart
• Mass extinction at end of period

Question 14

Jurassic Period

Answer 14

• Gymnosperms still dominant land plants
• Dinosaurs diversify and become dominant land animals
• First birds
• Modern fishes diversify

Question 15

Cretaceous Period

Answer 15

• Diversification of flowering plants, insects, fishes, and dinosaurs
• Mass extinction at end of period (eliminates dinosaurs)

Question 16

Cenozoic Era

Answer 16

65. 5 MYA - present day

- Paleogene, Neogene, Quaternary Periods

Question 17

Paleogene Period

Answer 17

• Modern birds and mammals appear
• Diversification of insects that pollinate flowers
• Continents near current position
• Modern animals appear
• Primates diversify
• Origin of apes

Question 18

Neogene Period

Answer 18

• Flowering plants and mammals diversify and are dominant on land
• Origin of human ancestors

Question 19

Quaternary Period

Answer 19

• Origin of modern humans

- Major glaciations