2: Concepts and Geological Time

Question 1

What is “Epistemology”? When was it started?

Answer 1

Epistemology: the philosophy of knowledge, started in the 18th century. It asks “how can we really KNOW something?”

The answer to that is through:
- faith
- intuition
- authority
- observation (the scientific method)

Question 2

What is Catastrophism? When was it started?

Answer 2

Catastrophism: the theory that changes in the earth’s crust (mountains, valleys) were caused from disasters like earthquakes, floods, etc.

Also linked to religious doctrine such as Noah’s Ark.

Question 3

What is uniformitarianism?

Answer 3

Uniformitarianism by James Hutton: the idea that the geological processes which are modifying the earth’s surface today must have acted in a similar manner in the past,

and that present day processes can be used to infer what environments existed in the past.

Question 4

What are some examples of uniformitarianism?

Answer 4

Ex/
- Pumice and obsidian in a lake/ocean could tell us that there used to be a volcano or lava there

• Fish fossils and petrified coral could tell us that there use to be lots of water there

Question 5

What is the Principle of Superposition?

Answer 5

In a sequence of bedded rocks, the rock layer above is younger than the ones below it

Question 6

What are cross-cutting relationships?

Answer 6

Igneous intrusions and faults are younger than the rocks that they intrude or break through

Question 7

What is the Principle of Original Horizontality?

Answer 7

Due to gravity, sedimentary rocks are deposited as horizontal layers.

If sedimentary rocks are folded (or faulted), this occurred AFTER deposition!

Question 8

What is the Principle of Lateral Continuity?

Answer 8

Rock units with similar characteristics can be correlated together even if they’re separated through erosion/exposure and plate tectonics.

Ex/ 10,000km of flat land had the same animal. Later, the land between 0 and 10,000 km are eroded, leaving a canyon. When we look at it now, the land looks disconnected and in no-way related, but looking at the fossils, we see that the same animal existed on both sides, allowing us to infer that the canyon was once flat land.

Question 9

What are unconformities?

Answer 9

Unconformities: represent breaks in geological records (erosional surfaces and missing rocks in expected sequences)

For example, Hutton’s Unconformity in Scotland:
- originally deposition making layered rock

• Deformation of strata in mountain-building event (the rock went from layers to wavy)
• Erosion produced a surface of unconformity (the wavy rock was cut down to a flat surface on top)
• Newer deposition making more layered-rock on top of wavy, deformed rock)
• Finally, the ground is uplifted, tilted, and eroded to produce the jagged, layered, unconformity we see today.

Question 10

What is the Principle of Biotic Succession?

Answer 10

Fossil content can be used to help determine the age of rock units that they’re found in because organisms have evolved and gone extinct through time, forming a specific order/timeline.

Question 11

What is the modern-day geological time scale?

Answer 11

Eon>Era>Period>Epoch
- Great Precambrian Expanse of time was too long, it’s its own thing.

First you have the Great Precambrian Expanse of time, divided into eons:
- Proterozoic: 2.5 Ga-545Ma (most recent)
- Archean: 2.5-4.0 Ga
- Hadean: 4.0-4.5 Ga (earliest when solar system was forming)

Visible Life Below

Then you have the eras in the MOST RECENT EON: Phanerozoic eon
<545 Ma
- Cenozoic Era (“recent life”),
- Mesozoic Era (“middle life”)
- Paleozoic Era (“ancient life”).

Question 12

Looking at the Geological Time Scale, what’s Relative time and Absolute time?

Answer 12

Relative time: age of units relative to one another
- Observed contact relationship between rock units
- Fossil records (comparing fossils in the unit being tested to fossil records from history)

Absolute time: specific age of whatever’s being tested in years

Question 13

What is Radiometric/Absolute Dating?

Answer 13

Radioisotopes (parents) are trapped in minerals when they crystallize and decay through time.

The ratio of parent to daughter isotopes reveals the number of half-lives and subsequently, the number of years since the mineral formed.

Parent - An unstable radioactive istope
Daughter - Stable Isotope; what you get when parent decays
Half-life - Time it takes for half of material to decay

Question 14

How much time does the Great Precambrian Expanse of Time take relative to the age of Earth?

Answer 14

The Precambrian (before observable life) era accounts for 87% of geologic time!