Week 9 - Stratigraphy and geologic time Flashcards
What is the principle of superposition?
Within a sequence of rock layers formed at Earth’s surface, rock layers lower in the sequence are older.
What two things can make the principle of superpositon to difficult to interpret?
- igneous rocks that form from volcanic activity may vertically cut through horizontally arranged layers of rocks
- mountain building events may tilt, fold, and even flip rock layers
What is stratigraphy?
It is the science of using the arrangement and composition of rock layers to interpret geological history.
What is a formation?
A large uninterrupted sequence of rock that’s made of multiple layers that share similar properties (such as mineral composition and average sediment grain size) and that all formed under similar conditions
Which technique is used to absolutely date rocks? What rocks cannot be dated using this technique (and why) and what are its implications?
Which technique is used to absolutely date rocks? Sedimentary rocks because it is made up of other rocks, so it’s never really new. Cannot use radiometric dating alone to determine the age of dino fossils.
How can sedimentary rocks be dated and what is a key tool in fossil dating?
by combining radiometric dating and the principle of superposition
if sedimentary rocks that contain fossils are found between two horizontal layer of igneous rock: igneous rock above –> the fossils must be older than; igneous rock below –> the fossils must be younger than
key tool in fossil dating = volcanic ash
What is the geological time scale?
It is a standard series of chronological divisions that parses Earth’s history.
What are the discrete named units that divide time, list in order of longer time period to shorter time period?
eons > eras > periods > epochs
What is the order of the eons?
Hadean(4.6-4 BYA), Archean(4-2.5 BYA), Proterozoic(2.5BYA-541 MYA), Phanerozoic(541 MYA - 0MYA)
What key events occured during the hadeon eon?
- Earth is born
- surface of the earth was partially molten and had high volcanic acitivty
- the moon was formed
- by the end: the earth and cooled and large oceans covered its surface
What key events happend during the archeon eon?
- oldest known fossils came from here: simple single-celled organisms
- more advanced forms later evolved in the Archean (e.g. cyanobacteria)
What are stromolites, what are they made of?
Cyanobacteria’s biofilms that trapped sediments (best record of early life)
What major events occurred during the Proterozoic eon ?
- early: first multicellular organisms evolved
- Ediacaran period: life forms with harder parts evolved, including animals
What eras are apart of the phanerzoic eon? Name in chronological order.
paleozoic, mesozoic and cenzoic eras
What periods occured during the paleozoic era? Name in chronological order?
Cambrian, ordovician, silurian, devonian, the carboniferous, and the permian period
