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: Eon – longest time unit on the scale Hadean (oldest) Archean Proterozoic Phanerozoic (youngest)

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

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.

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 org. 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