Lecture 6: stratigraphy

Question 1

lithostratigraphy

Answer 1

dating rocks based on their order and mineral composition
- Stratigraphic columns: maps that describe the vertical layering of rock in a particular location => can figure out which parts of the world were connected to each other
- When one rock is intruded by another, that rock that was already there must be older than intrusion
- young rocks on top and deeper you go, the older the rocks
- layers of rock are continuous until they encounter other bodies that block their deposition or until they are acted upon by agents that appeared after deposition took place (law of continuity)

Question 2

law of superposition

Answer 2

in undeformed stratigraphic sequences, the oldest strata lie at the bottom while the youngest strata are at the top => deeper you go, the farther back in time

Question 3

absolute time

Answer 3

way of calibrating geological time in rocks (numerical) through isometric dating; numeric age of a layer of rocks or fossils

Question 4

relative time

Answer 4

geologic age of a fossil organism, rock, or geologic feature or event defined

Question 5

biostratigraphy

Answer 5

dating rocks based on their fossils
- Index fossils: fossils from organisms that had a broad distribution but were short lived (very common!) => useful for correlating geologic columns between locations

Question 6

geochronology

Answer 6

earth time/provides absolute dates for strata

Question 7

strata

Answer 7

different layers of rock with different fossils

Question 8

radioactive decay

Answer 8

the process by which an unstable atom loses energy by radiation (found in igneous rocks)
- Nuclear physicists cannot predict when any individual atom will decay from a radioactive parent to daughter
- They can calculate how long it takes for groups of radioactive atoms to decay
- Half-life: the amount of time it takes for half of all radioactive atoms in a sample to decay
- Tend to use uranium when studying dinos

Question 9

Triassic

Answer 9

252-201 Ma
- first and oldest period of Mesozoic

Question 10

Jurassic

Answer 10

201-145 Ma
- second, middle period of Mesozoic
- 145 Mya total, named after limestone deposits in the Jura Mountains along the French/Swiss border
- True mammals appear & diversify
- Distribution of fossils: most found in northern continents

Question 11

Cretaceous

Answer 11

145-66 Ma
- third and final period of Mesozoic