1. Earth’s Geologic History
Chapter 9 Geologic Time
Earth’s Geologic History

2. 9-1 Geologic Time Earth’s surface is constantly changing
The scale, the Geologic Time Scale, outline the development of Earth & life on Earth
Stop at 1:29 and discuss the “ice age”.

3. Geologic Column
An ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.

4. How could millions of years be missing?

5. Fossils & The Geologic Time Scale

6. Fossils
Preserved remains or traces of an organism that lived in the past.
Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock.

7. Kinds of fossils
Petrified - when minerals replace the remains and they become rock
Mold - when the shell remains and the contents dissolve (hollow)
Cast - when the mold becomes filled with minerals that are not a part of the original organism

8. PETRIFIED MOLD
CAST

9. Dinosaur Tracks,
Texas

10. Where Fossils Occur Almost Exclusively in Sedimentary Rocks
Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil
Rare Exceptions:
Some Fossils in Low-grade Metamorphic Rocks
Trees Buried by Lava Flow
To Be Preserved, Organisms Have to Be:
Buried Rapidly After Death
Preserved From Decay

11. Fossils in a Geo Column
Fossils in the upper, more recent layers resemble modern plants and animals.
Fossils discovered in old layers are from species that have been extinct for millions of years.

12. How are they used?
Estimate the age of rock layers that cannot be dated radiometrically
COMPARE a given rock layer with a similar layer in the region that contains fossils.

13. Divisions of the Time Line
Geologists use the major changes of Earth’s surface, climate, and type of organisms to divide the time scale up.

14. Quaternary
Latin, “fourth”
1822
Tertiary
Latin, “third”
1760
Cretaceous
Latin creta, “chalk”
Jurassic
Jura Mountains, Switzerland
1795
Triassic
Latin, “three-fold”
1834
Permian
Perm, Russia
1841
Carboniferous
Carbon-bearing
Devonian
Devonshire, England
1840
Silurian
Silures, a pre-Roman tribe
1835
Ordovician
Ordovices, a pre-Roman tribe
1879
Cambrian
Latin Cambria, “Wales”

15. Eons and Eras, Period and Epochs
Largest unit of geologic time is an eon
Eons are divided into eras
Eras are divided into shorter time units called periods
Periods are divided into even shorter time units called epochs

17. Pre-Cambrian
Began with the formation of the Earth 4.6 billion years ago.
Bacteria appeared 3.5 billion years ago, followed by algae and fungi.

18. Paleozoic Era Divided into 5 periods:
Cambrian period - Sponges, snails, clams and worms evolve
Ordovician period - First fishes evolved and other species become extinct
Silurian period - Land plants, insects and spiders appear

19. Devonian period - Amphibians evolve and cone-bearing plants start to appear.
Carbonferous period - Tropical forests appear and reptiles evolve.
Permian period - Seed plants become common and insects and retiles become widespread. Sea animals and some amphibians begin to disappear.

20. Late Permian EXTINCTION
250 Million Years Ago
Nearly 90% of life became extinct
All trees died
Less than 5 % survived in the seas
Less than a third on land survived
Meteorite or a prolonged volcanic eruption

21. Mesozoic Era Divided into 3 periods:
Triassic period - Turtles and crocodiles evolve and dinosaurs appear.
Jurassic period - Large dinosaurs roam the world. First mammals and birds appear.
Cretaceous period - Flowering plants appear, mammals become more common, dinosaurs
become extinct.

22. Cenozoic Era Divided into 2 periods:
Tertiary period - First primates appear and flowering plants become the most common.
Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.

23. FYI Some Geologic Rates
Cutting of Grand Canyon
2 km/3 m.y. = 1 cm/15 yr
Uplift of Alps
5 km/10 m.y. = 1 cm/20 yr.
Opening of Atlantic
5000 km/180 m.y. = 2.8 cm/yr.
Uplift of White Mtns. (N.H.) Granites
8 km/150 m.y. = 1 cm/190 yr.

24. Movement of San Andreas Fault
5 cm/yr = 7 m/140 yr.
Growth of Mt. St. Helens
3 km/30,000 yr = 10 cm/yr.
Deposition of Niagara Dolomite
100 m/ 1 m.y.? = 1 cm/100 yr.

25. Lab: Geologic Timeline
Grouping by Bill Nye playing cards
5 meters of tape needed
Part 1 : Must convert the front page and make your prediction before starting
Part 2 : Creation of the timeline – BE PRECISE

26. Warm Up 11/15/12
Why is Precambrian time about 88 % of the timeline and not divided into smaller units based on the fossil record?
Many coal and oil deposits formed during Carboniferous Period. What element would you expect to find in both oil and coal?

27. 9-2 & 9-3