Geologic Time & Relative/Absolute Dating Notes
GEOLOGIC TIME
Divisions of Time: ______(longest), ______,______,______(shortest)
______(Present – 65 mya): “Age of Mammals”
______(65 mya – 248 mya): “Age of Reptiles”
______(248 mya – 543 mya): “Age of Invertebrates”
______(543 mya – 4.5 bya): “Time Before Life”
RELATIVE DATING
Process of placing events in the ______in which they occurred
Does ______identify actual dates
Uniformitarianism
The same processes that occur today also ______
______over time, not quick catastrophic events
Original Horizontality
Most ______rocks are deposited as a ______
Superposition
In an undisturbed sequence of sedimentary strata, the ______rock layer will be at the ______, and the ______on ______.
Cross-cutting
An igneous ______or ______is always ______than the rock it cuts through.
Uplift
Over time, rocks can be ______or deformed by regional or local metamorphism.
If rocks are ______, then the metamorphism that caused it is ______than the rocks.
New, younger rocks form ______of the tilted strata.
______- is a gap in the geologic record caused by erosion.
Fossils - help geologists study Earth’s past & determine…
- Approximately ______life began
- Which plants & animals were ______to live ______
How Fossils form:
Body must be ______from scavengersbacteria
Hard parts (like ______& ______) have a better
chance of becoming fossils
Fossils are found in ______rocks
Index Fossils
- Certain fossils can help find the ______of rocks.
- These special fossils are called ______.
Ex: ______ an ancient plant -lived 350-450 mya.
Ex: ______an ancient animal -lived 500-600 mya.
Types of Fossils
- Original Remains: Some substances (such as _____, ______, and ______) can fossilize organisms while preserving their remains
- Replaced Remains: Over time, organic material can be replaced by ______dissolved in water(Ex:Petrified wood)
- Molds & Casts: an organism is buried and then decomposes, leaving a cavity (or ______) that may fill in with minerals or rock (a ______)
- Trace Fossils: evidence of organisms without actual remains
Ex: ______, ______, ______, ______, bite marks
ABSOLUTE DATING
Determining the ______for events
Gives ages of rock in ______
Radioactive dating
The most ______method for determining age.
Radioactive elements give of particles and energy as they decay and new elements form.
Scientists know how long it takes for certain radioactive elements to decay, so they are like ______.
Radioactive decay
______: the time it takes for half the radioactive atoms in a sample to decay to a stable product.
Most absolute dating is done by measuring the amount of…
–______left over in fossils of plants & animals
–______left over in rocks older than 50,000
The instrument that measures radioactivity is a ______