Geologic Time Geologic Time Scale Divisions of Earths history - - PowerPoint PPT Presentation

Geologic Time

Geologic Time Scale

• Divisions of Earth’s

history based on life forms that were living during certain periods

• Separation =

Change.

• Correlate geologic

events, environmental changes, and changes among life forms

The Geologic Time Scale

• Record of Earth’s history
• Names of the time periods don’t

change but their boundaries are always being changed.

Scale is cut into different sections: 1) Eon – longest time unit on the scale

• Hadean (oldest)
• Archean
• Proterozoic
• Phanerozoic (youngest)

2) Era – next longest span of time

• Defined by the different life forms

that are found in the rocks. Marked by

major, striking, worldwide changes like mass extinction

• Precambrian (oldest)
• Paleozoic
• Mesozoic
• Cenozoic (youngest)

• Precambrian Era – microscopic life
• Paleozoic Era – Age of Trilobites
• Mesozoic Era – Age of Reptiles
• Cenozoic Era – Age of Mammals

3) Periods – defined by the life forms

that were abundant or became extinct during the time in which the rock was deposited. Third longest division of time.

4) Epochs – smaller division of

geologic time.

Trilobites

• Make excellent index

fossils b/c their characteristics changed every period

• Paleontologists uses

changes to determine the environment

Movement of Pangea

• Closed seas
• Formed mountains
• Not a completely acceptable explanation for

extinctions

Precambrian Time

• 4.5 billion yrs – 544 million yrs
• Longest part of Earth’s history
• Little known about org. in this time period b/c:

– 4 million yr old rock buried deeply and experiences enough heat & pressure to destroy fossils – Most org. had soft parts

Precambrian Time

• How life changed:

– Cyanobacteria – algae that photosynthesized producing O2 – O2 created ozone layer allowing the evolution of more complex organisms – Invertebrates – (no backbone) appeared towards end of Precambrian Time

• Ex: jellyfish, worms

Precambrian Time

• End:

– Extinctions – New org. out-competed old org. – Scientists not completely sure

Paleozoic Era – Era of Ancient Life

• 544 million yrs – 248

million yrs

• How life changed:

– mostly marine org. so large seas – Trilobites and shelled

• rg. common so

abundance of fossils

Paleozoic Era

– Vertebrates (backbone) evolved – Forest appeared – gymnosperms – plants producing seeds only – Vertebrates began to adapt to land = amphibians

• ex. Frog
• Purpose was org. needed to survive in oxygen poor

waters

• Can’t keep moisture in their bodies and need water to

lay their eggs

Paleozoic Era

– Several mtn. building episodes – Appalachian Mountains formed

• End:

– 90% of marine, 70% land species died – Volcanoes? – Asteroid/comet collision?

Mesozoic Era – Middle Life

• 248 million yrs – 65 million yrs
• How life changed:

– Pangea seperated into 2 landmasses Laurasia, Gondwanaland – Reptiles – Dinosaurs

Mesozoic Era

– Birds appeared during Jurassic Period – Mammals appeared during Triassic Period – Angiosperms – flowering plants – started evolving during Cretaceous Period

Mesozoic Era

• End:

– Mass extinction – Comet/asteroid collision causing dust/smoke to block out sun – Some survivors

Cenozoic Era – Recent Life

• 65 million yrs – present
• How life changed:

– Mountain building episode: Alps, Andes, Himalayas – Grassland expansion – grazing mammals become larger

Cenozoic Era

– Continents split further, org. became isolated and began to evolve

• Marsupials – koala, wombat, kangeroos

– HUMANS