CH 12, Section 1: Discovering Earth's History
What is uniformitarianism?
Uniformitarianism - the idea that the physical, chemical, and biological laws that operate today, also operated in the past
What is a fossil?
What does the Geologic Time Scale represent?
The Geologic Time Scale represents the 4.6 billion years that have passed since the first rocks formed on Earth.
SECTION 2: What are unaltered remains?
Unaltered remains - freezing or tree amber can preserve a fossil in almost original condition
What is relative dating?
Relative dating - a method geologists use to place rocks in chronological order
Fill in the blank with the provided answers:
(Soft/Hard) parts of an organism decay faster, (soft/hard), which include shells and bones, are more commonly preserved over time.
SOFT parts of an organism decay faster, HARD parts, which include shells and bones, are more commonly preserved over time.
How is time divided?
Time is divided into large blocks with each block dividing into smaller blocks.
SECTION 2: What are trace fossils?
Trace fossils are the indirect evidence of prehistoric life. EX: tracks, footprints, burrows
What is superposition?
Superposition - in an undeformed sequence of sedimentary rocks, each layer is older than the one above it and younger than the one below it
How do petrified fossils form?
Petrified fossils form because mineral-rich water soaks into the small cavities and pores of organic tissue such as shell, bone, or wood. As minerals precipitate, they fill the spaces and replace the dissolving tissue.
How are eons, eras, and periods divided?
Eons - longest interval and is divided into eras
Eras - second longest interval and is divided into periods
Periods - third longest interval and is divided into epochs
SECTION 2: What are index fossils?
Index fossils - fossils of organisms that lived during a relative short, well-defined geologic time span
What is the principal of original horizontality?
Principal of original horizontality - sediment is generally deposited in flat, horizontal layers
What's the difference between casts and molds?
Molds are cavities in rock where a plant or animal was buried. It reflects the shape and surface markings of an organism.
Casts are created when minerals or sediments fills a mold.
How is the current Eon divided into?
The current eon is divided into the following eras:
Paleozoic: began 542 million years ago--known for aquatic invertebrates
Mesozoic: began 251 million years ago--known as the age of reptiles
Cenozoic: began 65 million years ago--known as the age of mammals
What is the principal of cross-cutting relationships?
Principle of cross-cutting relationships - if disturbances occur, they are thought to have occurred after deposition
What is a compression fossil? NOTE: Name how it forms as well
Compression fossil - 2-dimensional organic remains
Forms when pressure squeezes out liquids and gases from a buried organism, leaving behind only a delicate, thin film of carbon.
Precambrian time is the time before the current Eon (it makes up the first three eons). Not a lot of fossils are found in this rock. There were single celled organisms and some invertebrates towards the end of Precambrian time.