Lecture 7 Pt.2

Question 1

Uncomformities

Answer 1

Ancient erosional surface that represents a time gap or a hiatus. There are 3 types:

1. Angular uncomformity
2. Discomformity
3. Noncomformity

Question 2

Angular discomformity

Answer 2

Different orientations above and below

Angle->erosion->deposition of rock

Question 3

Discomformity

Answer 3

Strata have same orientation above and below

No obvious visual quo that there is a gap in time

Question 4

Nondiscomformity

Answer 4

Unit below is not sedimentary

2 different rock types associated with each other where we know one is older than the other (e.g. igneous and then sedimentary)

Question 5

Development of geologic time scale

Answer 5

• methods of relative dating of strata were used to first develop a geological time scale
• numerical ages were then added subsequently by using isotopic methods
• to this day, many boundaries are defined by fossils

Question 6

K-T boundary

Answer 6

Croatian timescale

Review chart in lecture slides

Question 7

What lead Hutton to think of the Earth as older than it is

Answer 7

It’s stratigraphy

Question 8

How the GTS was built

Answer 8

• Lord Kelvin: magma cooling (20-100 million years)
• John Joly: estimated how long it would have taken for the oceans to accumulate salt from erosion processes. 80-100 million years old. Used radioactivity too
• Samuel Haughton: used stratigraphic thickness and deposition rates to come up with the age of 200 million years
• Arthur Holmes: in The Age of The Earth, reviewed and added to all available radiometric ages and came up with a rough sketch of a Geologic Time Scale

Question 9

The original GTS had

Answer 9

Four time division:

Primary, secondary, tertiary, quaternary (only one left)

Question 10

ASIC structure of GTS

Answer 10

1. Eons (4)
2. Eras (10)
3. Periods (22-10)
4. Epochs (lots)
5. Age (even more)

Question 11

Hadean Eon

Answer 11

• 4.5-4.0 GA
• period before earliest known rock
• heating from radioactive decay melted most of early Earth
• intense meteorite bombardment forming moon (between 4-4.2 GA)

Question 12

Archean Eon

Answer 12

• starts with earliest known rocks-4.0 GA
• interior of earth was hotter than now (more radioactive isotopes)
• atmosphere mainly CO2, nitrogen, methane
• first signs of life around 3.5 GA (stromatolites)

Question 13

Proterozoic Eon

Answer 13

• start defined at 2.5 GA
• tectonic system probably similar to today’s
• single called organisms became abundant
• “Great Oxygenation Event”
• Birth of multicellular organisms

Question 14

Phanerozoic Eon: Paleozoic Era

Answer 14

• starts with first Shelly fossils (545 MA) known as Cambrian explosions
• things start creeping out of the ocean
• “the Great Dying” (end of permian extinction)
• defined by 6 systems that saw major leaps in the evolution of modern Earth systems and biology

Question 15

Paleozoic Era summary

Answer 15

-review chart

Question 16

Phanerozoic Eon: Mesozoic era

Answer 16

• starts with “The Great Dying” and ends with another ~65 MA (K-T boundary)
• age of dinosaurs on land
• giants ruled the sea, land and sky
• three famous periods

Question 17

Mesozoic era

Answer 17

Review summary chart

Question 18

Phanerozoic Erin: Cenozoic Era

Answer 18

• starts at a major extinction event ~65 MA

- continues to today

Question 19

Cenozoic Era summary

Answer 19

• the age of mammals
• general cooling to the “ice Age” defined by the quaternary
• Holocene is today but debate about Anthropocene