Name:
PD.
Unit 3B – The Lithosphere
3.4 Earth’s Geologic History Notes
1. Relative Age Dating
a.
2.
Uniformitarianism
i. means the forces and processes we see today have been at work for a very ______________ time.
ii. “The present is the key to the past”
b. Relative dating
i. Tells us the _________________ in which events occurred, not how _____________________ they
occurred.
c. Law of superposition
i. States that in an undeformed (NOT folded NOR tilted) sequence of sedimentary rocks, each bed is
_____________ than one above it and __________________ than the one below it.
d. Principle of Original Horizontality
i. Layers of sediment are initially deposited in a ______________________ position.
e. Principle of Cross-Cutting Relationships
i. When a fault __________ through rock layers or ______________ intrudes other rocks, we can assume
the fault or magma intrusion is ________________ than the rocks it affects.
f. Inclusions
i. Inclusions are rocks ______________________________ other rocks
ii. Rocks containing intrusions are _________________ than the inclusions they have
g. Unconformities
i. a long period which deposition ___________________, erosion removed past rocks, and then deposition
of new material _________________
ii. 3 types of unconformities:
1. Angular unconformity – during the pause in deposition, a period of _____________________
(folding or tilting) and erosion occurred.
2. Nonconformity – when sedimentary rock lies above and was deposited on top of existing
_____________ or________________ rock
3. Disconformity – when two sedimentary rock layers are separated by an
____________________________
Absolute Age Dating
a. Dating with Radioactivity
i. Radioactivity is the spontaneous _______________ of certain unstable atoms
ii. Half-life is the amount of ____________ necessary for ________________ of the atoms in a sample to
decay to a STABLE isotope (stable version)
1. Isotopes are different versions of the same elements, they just have a different number of
neutrons
iii. Radioactive isotopes decay at a _________________ rate since the formation of the rock they occur in
iv. Radiometric dating is the procedure of calculating ____________________ ages of rocks/minerals
containing radioactive isotopes
v. As radioactive (PARENT) isotope decays, atoms of the stable (DAUGHTER) product form
b. Example – Dating with Carbon-14
i. Radiocarbon dating is the method for finding age by comparing amount of carbon-14 (parent) to amount
of carbon-12(daughter) in a sample
ii. When an organism dies, the amount of carbon-14 decreases as it decays. By looking at the ratio of
carbon-14 to carbon-12 in a sample, _____________ can be determined
c. Importance of Radiometric dating
i. It has supported ideas of James Hutton, Charles Darwin, and other scientists who inferred that geologic
time must be IMMENSE.
3.
4.
The Fossil Record
a. Fossil Formation
i. Fossils are the ______________ or _____________ of prehistoric life. They are important parts of
sediment/sedimentary rocks.
1. The type of fossil that is formed is determined by the __________________________ and
________________________.
ii. Unaltered remains
1. Some remains of organisms – such teeth, ____________, and shells – may not have been altered
(hardly changed at all over time)
iii. Altered remains
1. The remains of an organism are likely to be changed over time
2. Fossils often become ______________ (organic parts replaced with minerals) or turned to
____________
3. Molds – organism dies, covered by sediment, its flesh and bone decays, and leaves a
_______________ of what it looks like
4. Casts – created if the hollow spaces of a mold are filled with ________________ matter
5. Carbon films – organic material is compressed, leaving only a __________________ residue
iv. Indirect Evidence
1. Trace fossils are indirect evidence of prehistoric life (_________________, burrows, coprolite)
v. Conditions Favoring Preservation
1. two conditions are important for preservation:
a. _________________________
b. _________________________
b. Fossils and Correlation
i. Principle of fossil succession:
1. Fossil organisms _____________ (come after) one another in a definite order. Therefore, any
time period can be figured out by its fossil content.
ii. Index fossils
1. Are _______________ on Earth, are limited to a _____________ span of time, and occur in
____________ numbers
a. Tool for determining age of rock layers
iii. Interpreting environments
1. Fossils can be used to interpret and describe ancient environments
2. For example, suppose geologists found fossil clam shells in a bed of limestone. They can infer
that the region was once covered by a shallow sea.
Geologic Time
a. Structure of the Time Scale
i. Geologic time scale is a _________________ that divides Earth’s history into units representing specific
_______________ of time.
ii. __________ represent the greatest expanses of time
iii. Eons are divided into _____________
iv. Each era is subdivided into ______________
v. Periods are divided into smaller units called _______________
b. Precambrian Time – Vast and Puzzling
i. Time frame: ___________ billion years ago to __________ million years ago
ii. Rocks were large masses of ___________________ rock (SHIELDS)
iii. Atmosphere was water vapor, ___________, nitrous oxide, NO OXYGEN (anoxic)
iv. Oxygen began to build up ______ billion years ago due to the evolution of ____________________ plants
v. Most common Precambrian fossils are _____________________ - layered mounds of Calcium Carbonate
made from algae
c. Paleozoic Era – Life Explodes
i. Time frame: __________ million years ago to _______ million years ago
ii. By the end of the Paleozoic, all continents had fused into the supercontinent ____________________
d.
e.
iii. Life in _____________ Paleozoic was restricted to _____________.
iv. Late Paleozoic:
1. Some 400 million years ago, plants had adapted to live at water’s ___________, began to move
inland, becoming ____________ plants
2. Amphibians rapidly ____________________ because they had minimal _______________ from
other land dwellers
Mesozoic Era: Age of Reptiles
i. Time frame: _________ million years ago to __________ million years ago
ii. Major tectonic event broke up Pangaea
iii. Seed-producing plants (________________) quickly became dominant
iv. With perfection of _____________ egg, reptiles quickly became dominant land animals
v. At end of Mesozoic, many reptile groups became extinct
1. Due to large meteorite that collided with Earth
2. Bye-bye dinosaurs!
Cenozoic Era – Age of Mammals
i. Time frame: _______ million years ago to present
ii. ______________________ caused many events of mountain building, volcanism, and earthquakes
iii. ______________ replaced reptiles as dominant land animals
iv. ______________ - flowering plants with covered seeds – replaced gymnosperms as dominant land plants
v. With extinction of dinosaurs, mammals diversified, forming many new groups including _________ and
__________.