1. Geologic Time & Earth’s Evolution
Piecing together Earth’s history
Relative Dating
Using laws of superposition, cross cutting, etc. to determine a sequence of events (this happened, then that)
Index Fossils – constrain (pin down) a time range when a rock layer was deposited.
Fossils of extinct organisms, that were wide spread, and lived during a specific period of time.
Example: Trilobites

2. Relative Dating: Index Fossils

3. Ch 23.6: Geologic Time & Earth’s Evolution
Piecing together Earth’s history
Absolute Dating
Radioactive elements in rocks, like uranium, potassium, carbon, breakdown at a known rate. If you know how much was in the initial sample … you can determine age. (Isotopic dating)
How Earth was Made, Part 1:

4. Ch 23.6: Geologic Time & Earth’s Evolution
ERAS & PERIODS
Why all the divisions?
To manage Earth’s history, geologists have divided Earth’s history into EONS. Eons are divided into ERAS. Eras are divided into PERIODS. Periods are divided into EPOCHS.
You need to know the major developments in terms of life forms, tectonics, atmosphere and climate for each ERA.

5. Geo. Time is broken up into ERAS (based on life forms and enviro.)
Cenozoic (now – 65 mya)
Mesozoic (254 ma)
Paleozoic (540 ma)
All time before that = Precambrian (540 ma – 4.6 billion)
ERAS are NOT EQUAL in TIME.
The Precambrian was the longest ERA. It took Earth a LONG time to be suitable for complex life.
Each era ends with a mass extinction followed by a burst of speciation.

6. Mass Extinctions: Punctuate E’s History
Between each Era (and some periods)

7. Mass Extinctions = High % of species go extinct
Species that are better suited to environment are successful, reproduce, and evolve.
Causes: Meteor impact; Volcanism; Glaciation; anything that can change atmosphere, climate, or environmental conditions.

8. CH 23.6 Geologic Time and Earth’s Evolution
Complex multicellular life is a “recent” development.

9. Precambrian
Fossils from this time are not abundant in the rock record because most organisms are “soft bodied” – no skeletons or shells.

10. Precambrian: 4.5 billion – 540 ma
Earth starts off as MOLTEN and VOLCANIC
Atmosphere = CO2, CH4(methane), H2O= Green house gases
Oceans form and first continents form when Earth cools
Origin of water = volcanic steam & meteorites (comets)
1st life = bacteria (single celled) 3.5 bya - use chemosynthesis (not sunlight) for energy. They can withstand extreme conditions.

11. Precambrian: 4.5 billion – 540 ma
Cyanobacteria (blue-green algae)
~ 3 bya – take in CO2 and release O2 (photosynth)  PLANET CHANGING!
Temps. Decrease (take in CO2)
Oxygen makes O3 = OZONE LAYER  Shields surface from UV radiation (UV kills cells)
O2 atmosphere– more complex organisms to develop!
Simple multicellular organisms in shallow seas
1st Supercontinent (Rhodinia)
MASS EXTINCTION = SNOW BALL EARTH  ICE AGE! Closes PRECAMBRIAN

12. Paleozoic Era

13. Paleozoic Era: 540 – 245 mya
CAMBRIAN EXPLOSION starts off ERA – “explosion” in the diversity of life forms
Snowball Earth is thawed by millions of years of volcanic activity.
Warm temperatures
LIFE IN SHALLOW SEAS
½ through, life “invades” land (amphibians, land plants, insects) (Thank you Ozone)

14. Paleozoic Era: 540 – 245 mya
Early GIANT FORESTS/Swamps become our fossil fuels (Buried, but not decomposed plant and animal matter  fossil fuels)
Pangaea assembles  Interior of continent becomes DRY and COOL(favors reptiles etc)
Ends with…
MASS EXTINCTION = “GREAT DYING”
Volcanic activity? Lava flows in Siberia for millions of years change climate?

15. Mesozoic

16. Mesozoic Era: 245 - 65 mya AGE of DINOs
WARM and subtropical environment
Virtually ice-free
Pangaea rifts apart
1st Flowering plants; Giant insects; birds
Mammals appear (small)
Ends with…
MASS EXTINCTION = ASTEROID IMPACT = K-T EVENT (+ Lava flows in India)
Meteoroid impact in the Gulf of Mexico

17. Cenozoic

18. Cenozoic Era: 65 mya - present
AGE of Mammals
ICE AGES – Glaciers advance and retreat
Ocean currents change due to new continent positions; Mt. Building changes air circulation
Hominids (human ancestors) – 2 mya; Modern humans – 200,000 yrs
Global Mountain building - affect air circulation  drier & cooler conditions
Cooler & Drier  Grasslands (not tropical forests)
When glaciers grow …
Sea level drops
More land is exposed (land bridges)
Ends with… ?????

19. What does a mass extinction look like in the Rock Record?
Black layer = carbon rich; carbon from organisms that died abruptly and could not all be decomposed; carbon in organism changes w/heat and pressure to become oil/coal.
White layer = Debris from asteroid/impact

20. Meteoroid that hit 65 mya caused a Mass Extinction
75% Species on planet go extinct.
90% of planktonic life in ocean die (plankton supports the oceanic food chain).
Takes 10,000 years to recover.

23. How do we know when Meteoroids have hit Earth in the Past?
Look for … in the rock layer
Iridium – an element not common on Earth but common on meteroids (asteroids or comets)
Shocked Quartz – heat changes quartz grains
Tektites - quartz grains vaporized and cooled so fast they turn in to glass beads.
K-T Boundary: This layer is found on every continent in rocks 65 my old.

24. K-T Extinction
When: 65 million years ago (End of Cretaceous- Beginning of Tertiary Periods) Where: Chicxulub – Yucatan Pennisula Mexico What: Asteriod or Comet – 10km in diameter makes a crater 180 km in diameter. Impact Event: 100 MillioMegatons TNT (6 x more energetic than 1980 Mt. St. Helen’s eruption) Results– Fires; Magnitude 10 Eqs; Tsunamis; Climate change; Volcanism; Mass extinction (collapse of ocean food chain & bye-bye dinosaurs)

26. Human Evolution & Hominids
Evolution of Early Humans
Cave paintings
Evolutionary Tree