ESSC EXAM 1 - Geologic Time

Main beliefs of catastrophism?

Earth shaped by multiple divine catastrophes. Biggest was Noah’s flood. Earth only a few thousand years old

The guy behind catatrophism?

James Ussher

What uncovered the fundamental principals of modern geology?

Uniformitatianism

Lord Kelvin (believed uniformitarianism) used the cooling rate of rock to determine the age of the Earth. He concluded Earth has lost heat at a constant, linear rate. What did he not know about?

Radiation/radioactive decay that caused the heating and cooling of Earth to be nonlinear

Who published Theory of the Earth in the 1700s that birthed modern geology?

James Hutton

Can relative dating give an exact number?

No. It only tells you the sequence of events

With relative dating, what is the Law of Superposition?

Oldest rocks on the bottom, youngest on top.

Relative dating, what is the principle of horizontality?

Sediment/rock is depositied horizontally

Relative dating, cross-cutting principle?

Younger features cut through older ones

According to the principle of inclusion, is the rock contained within the other rock younger or older?

Younger

What’s an unconformity?

A break in the rock record, usually showing as a squiggly line

Angular unconformity?

Tilted rocks are overlain (lay on top of) flat ones; AKA the non-parallel rocks

Disconformity?

The rocks between the squiggle are parallel

Nonconformity?

Metamorphic or igneous rocks below, younger sedimentary rocks above; nonlayered rock is uplifted and eroded, then erosion surface buried by sediment

Correlation?

Matching layers of rock - strata - of similar ages in different regions; usually involves fossils

What can correlation use and which is the biggest helper?

Magnetic sequence (biggest helper), fossils, rock type, position in sequence, and numeric age.

What are fossils?

Remains or traces of prehistoric life

What are the direct types of fossil evidence?

Mold, cast, petrified, formed by replacement, carbonization, impression, preservation in amber

Fossil mold?

shell or other structure is buried and then dissolved by underground water

Fossil petrified?

cavities and pores filled with precipitated mineral matter

Fossil formed by replacement?

cell material is removed and replaced with mineral matter

Fossil by carbonization?

organic matter becomes a thin residue of carbon. Get Pompeii’d loser

Impression fossil?

replica of the fossil’s surface preserved in fine-grained sediment

Fossilization by preservation in amber?

hardened resin of ancient trees surrounds an organism

Indirect types of fossils?

Corprolites, burrows, tracks, gastroliths, and stromatolites

What are coprolites?

Shit and stomach stuff

What are gastroliths?

Stomach stones swallowed to help break down food

What are stromatolites?

Bacterial mats that were covered in sand; fossilized constructed feature

What conditions favor preservation?

Rapid burial; possession of hard parts (e.g., exoskeletons, bones); marine life more likely to be fossilized

What is the principle of fossil succession (aka principle of fauna and flora succession)?

Fossils succeed one another in a definite and determinable order, simple ones on the bottom strata and the higher ones contain complex and simple organisms

Who proposed fossil/flaural/faunal succession and when?

William Smith in the late 1700s/early 1800s

What does the suffix zoic mean when referring to geologic time periods?

Life

What must fossils have to be considered an index fossil?

The bastard was in lots of places for a short amount of time

Isotope?

A variant of the same parent atom, but there’s a different amount of neutrons and mass number (proton number is the same)

Difference between parent and daughter isotope?

Parent is unstable, daughter forms from the decay of the parent

Radioactivity?

Decay of atomic nuclei

Half-life?

The amount of time it takes for half of parents/radioactive nuclei to decay; everyone has a different decay rate

Radiometric dating is AKA?

Absolute dating

What are the best conditions for radiometric dating?

Requires a closed system; wants a pure and undisturbed sample as possible; best with igneous rocks; cross-checks for accuracy

Does radiometric dating give a numeric date?

Yes

What do isotopic ages tell us?

Age of eruption, age of solidification, age of metamorphic events, when rock cooled, age of source of sediment, age of recent sediment

Carbon-14 dating is used to date very ___ events, and is produced in ___. However, it cannot be used to date dinosaurs. 

recent; upper atmosphere;

In order of largest time scale to smallest, list the units of geologic history (originally created using relative dates)

Eons, eras, periods, epochs

What are the four eons (listed youngest to oldest)?

Phanerozoic (visible life), proterozoic (microscopic), archean, hadean (the oldest)

What are the eras of the phanerozoic eon?

Cenozoic (recent life), mesozoic (middle life), and paleozoic (ancient life)

Between uniformitarianism and catastrophism, which is more scientifically aligned with modern geology?

Uniformitarianism

How does a typical landscape form?

Preexisting rock covered by sea→ sea deposits layer of sediment (subarea exposure) → environment changes, depositing more rock AND/OR deposition stops → area eroded by rivers, etc. → continued erosion

When oceans come onto the continent(s), it’s called ___; when it moves away from the continent(s), it is called ___.

Transgression; regression

Unlike relative dating, what can radiometric (aka isotopic) dating do? What does it use?

Give specific numbers/time periods to rocks; uses igneous intrusions/rock and fossils

The actual age of rocks that cannot be dated isotopically can sometimes be ascertained by ___

Correlation

The geologic time scale was originally created using ___ dates.

Relative