7th Grade The Rock and Fossil
Section 1- Earth’s Story and Those Who First Listened
1. The Principle of Uniformitarianism
a. Processes that we observe today-such as erosion and
deposition do not change over time-still going on.
b. Catastrophism- is the principle that states that all
geologic changes occur suddenly—rapid changes
2. Modern Geology- A Happy Medium
a. States that both uniformitarianism and catastrophism
both helped form the earth.
3. Paleontology- study of the past life on the earth
• Section 2—Relative Dating: Which Came
• Relative Dating- determining if an object is
older or younger than other objects.
• 1. The Principle of Superposition
• a. The principle states younger rocks lie
above older rocks.
• b. Disturbing Forces
• a. Forces change this by tilting, folding and
breaking into movable forces.
• 2. The Geologic Column—arrangement of
rock layers in which oldest are at the bottom.
• 3. Disturbed Rock Layer
• a. Fault-break in the earth’s crust where blocks of crust slide relative
to each other
• b. Intrusion- molten rock from the interior squeezes into existing rock
• c. Folding—when layers bend and buckle.
• d. Tilting-internal forces in the Earth slant rock layers.
• 4. Gaps in the Record-Unconformities
• a. Layers of rock missing completely
• b. Missing evidence- Unconformity is a surface that represents a
missing part in the geologic column.
• i. Nondeposition- stoppage of deposition when sediment is cut off
• 5. Types of Unconformities
• a. Disconformities
• Section 3—Absolute Dating: A Measure of Time
• Absolute Dating- telling the age of an object by determining
how long it has existed.
• 1. Radioactive Decay
• a. Isotopes- an element with the same number of protons, but a
• different number of electrons.
• b. Most are stable, meaning they stay in their normal form.
Some are unstable.
• c. Unstable isotopes are called radioactive
• 1. Parent isotope- unstable
• 2. Daughter isotope- stable isotope produced by the decay of
the parent isotope.
• 2. Radiometric Dating
• a. based on the ratio of parent material to the daughter material
• b. half-life is the time it takes one half of a radioactive sample to
Looking at Fossils
• Fossilized Organisms
– Fossil-remains or physical evidence of an organism
• Fossils in Rocks
– Hard parts of animals- shells & bones
• Fossils in Amber
– Amber-hardened tree sap
– Minerals replace an organism’s tissue
– Permineralization-the pore space (bone or wood) is
replaced by minerals
– Fossils in Asphalt
• LaBrea asphalt pits
– Frozen Fossils
• Preserved from the last ice age
• Other Types of Fossils
– Trace Fossils
• Naturally preserved evidence of animal activity
– Molds and Casts
• Mold –cavity where the animal is buried
• Cast-an object created when sediment fills in a mold.
• Using Fossils to Interpret the Past
– The information in the Fossil Record
• Rough sketch of the history of life on earth
• History of Environmental Change
– Marine fossils on a mountain top
– History of Changing Organisms
• Only a small portion of animals have been fossilized
• Using Fossils to Date Rocks--Index Fossils are
fossils of organisms that lived in a very short
well defined geologic time span
– Ammontes called Tropites index fossil of 230-208
million years ago.
– Trilobites called Phacops 400 million years ago.
Time Marches On
• Geologic Time
– The Rock Record and Geologic Time
– The Fossil Record and Geologic Time
• The Geologic Time Scale
– Divisions of Time
• Eons-largest- 4 of these
• Eras-second largest- 3 of them
• Periods-third largest
• Epochs-fourth largest
– The Appearance and Disappearance of
• Extinction-no longer living – all of that species are
– The Paleozoic Era-Old Life
– The Mesozoic Era-The Age of Reptiles
– The Cenozoic Era- The Age of Mammals