Earth History -The Geologic Time Scale

The Age of the Earth4.6 billion years

old =4,600,000,000

The earth’s 4.6 billion year history is divided

into major units of time:

Cenozoic Era

Mesozoic Era

Paleozoic Era

Precambrian Time

Precambrian Time• 4.6 billion years before present

to 544 million years before present

• Longest era with a sparse fossil record

• Origin of earth’s crust, first atmosphere, and first seas

• Earliest fossils of cyanobacteria use photosynthesis to produce oxygen

• Ozone layer in the atmosphere is formed from oxygen

Paleozoic era

• 544 million years before present to 245 million years before present

• Marine communities flourish

• Early fishes develop

• Origin of amphibians, insects & reptiles

• Recurring ice ages/ Appalachians mountains form

• Spore-bearing plants dominate

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Paleozoic era (continued)…

• 286 - 248 million years before present: Supercontinent of Pangea forms

• 248 million years before present: MASS EXTINCTION-90 % of all known families lost!

.

c

Mesozoic Era

• 245 million years before present - 65 million years before present

• The age of the dinosaurs!

• Gymnosperms dominate land plant/ origin of angiosperms - flowering plants

• Origin of mammals & birds

• 145 million years before present - asteroid impact? MASS EXTINCTION

• Pangea begins to separate/ Rocky mountains form

65 million years before present….

• ASTEROID IMPACT!

• Mass extinction of ALL dinosaurs and many marine organisms

• End of the Mesozoic era

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Cenozoic Era

• 65 million years before present -today

• Present era we live in

• Continued evolution and adaptations of flowering plants, insects, birds, mammals

• Mammals dominant

• Major crustal movements & mountain building (Alps & Himalayan mountains form)

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And during the Cenozoic era…

• The most primitive hominid (human ancestor) evolves - approximately 4.4million years before present

• The first modern humans (homo sapiens) evolved approximately 100,000 years before present

Image courtesy of: http://www.wilderdom.com/images/evolution/8.jpg

Assignment – You can use your Textbook and your cell Phones

• Describe the Experiments of Louis Pasteur and Alexander Oparin and Stanley Miller in relation to Formation of First Cells on Earth.

• Bacteria were the first living cells on earth. How did Eukaryotic or Multicellular organisms came into being. Describe Endosymbiosis.