Paleography

Question 1

Geologic time scale

Answer 1

• About 4 billion years ago first life appeared on Earth.
• 3.2 billion years ago first photosynthetic organisms
• 2.3 billion years ago oxygen concentrations increase till oxygen rich.
• 5.3 million years ago the Cambrian explosion.
• 230 – 66 million years ago first non-avian dinosaurs

Question 2

Atmospheric composition since the origin

Answer 2

-First higher concentrations of methane, carbon dioxide and water
-About 1 million years ago increase in oxygen

Question 3

Milankovic theory based on two key ideas:

Answer 3

1. Earth’s climate is strongly affected by how much sunlight the northern latitudes receive during the summers.
2. This amount of sunlight varies based on changes of the Earth’s orbit and rotation.

Question 4

Why are the northern latitudes so important? (explain in 5 steps)

Answer 4

Due to ice. The colder it is the more ice is present. Ice reflects sunlight back, preventing heating of the surface, making it even colder. There is way more ice in the northern hemisphere because there is more land.

During the winter the ice caps in the Arctic grow. This is true no matter what is going on with the Earth’s orbit.

the key variable is how much ice melts during the summer. This depends on how much sunlight there is during the summer.

Milankovic showed that over thousands of years the amount of summer sunlight can shift plus or minus 15%
- This can bring and end ice-ages.

Question 5

Effects of Milankovic (3 cycles)

Answer 5

1. The first cycle concerns precession (13,500 - 29,000 years)
2. The second cycle concerns obliquity (approx. 41,000 years)
3. the third cycle refers to eccentricity (100,000 years)

Question 6

precession

Answer 6

The first cycle concerns precession (13,500 - 29,000 years) and refers to the direction of the angle that the central axis of the earth makes in relation to the sun.

Question 7

obliquity

Answer 7

Relates to the degree of angle of the central axis of the earth. The tilt of Earth’s axis changes between about 22° and 24.5°. A larger tilt means more extreme seasons (hotter summers, colder winters), while a smaller tilt makes seasons milder.

Question 8

Eccentricity

Answer 8

The shape of Earth’s orbit changes from more circular to more elliptical. This affects the difference in distance to the Sun, influencing how much solar energy Earth receives.

Question 9

precession

Answer 9

and refers to the direction of the angle that the central axis of the earth makes in relation to the sun. This moderates seasons

Sun is now furthest away in july from north pole, but the earth axis spins, so this changes. 30.000 years ago tilt was reversed. When earth was closest to the sun, it was summer in the north, so seasons were more extreme. Warmer summer, more melting, even warmer.

Question 10

Name 8 other feedback factors that play a role

Answer 10

1. Precipitation
2. evaporation
3. cloud formation
4. dominant wind patterns
5. sea level
6. ocean currents
7. albedo.
8. atmospheric composition

Question 11

Albedo

Answer 11

The ability of a given surface to reflect solar radiation. Fresh snow or ice reflects about 60-90% of the radiation, but water only does around 5-10%.

Question 12

atmospheric composition

Answer 12

When Earth cools, oceans become colder and can dissolve more CO₂ from the atmosphere. This lowers atmospheric CO₂, weakening the greenhouse effect and causing further cooling. The extra cooling allows more ice to form, which reflects more sunlight, reinforcing the process and potentially leading to an ice age.

Question 13

Ocean current

Answer 13

can either contain warm (shallow) or cold (deep, more salt) water. These currents influence the land it passes, either preventing the freezing of water during the winter or the other way around.

Question 14

Role of volcanos

Answer 14

Cooling effect: increase albedo (more clouds or particles in the air), warming effect: increased CO2 levels. Short term effects may last for years.

Question 15

Marine Isotope Stages (MIS)

Answer 15

During cold periods, more ¹⁶O is stored in ice sheets, so oceans contain relatively more ¹⁸O. This higher ¹⁸O/¹⁶O ratio is recorded in shells of marine organisms and used to reconstruct past climates.

Marine Isotope Stages are alternating warm and cold periods in Earth’s past, identified from oxygen isotope ratios (¹⁸O/¹⁶O) in deep-sea sediments. Even-numbered stages are cold (glacial periods), and odd-numbered stages are warm (interglacials).

Question 16

Ice Cap origination and the glaciation threshold

Answer 16

insolation of preglacial phase is the amount of incoming solar radiation (insolation)

The glaciation threshold is the critical level of summer insolation below which ice sheets can grow year after year. When insolation drops below this threshold, melting is insufficient, snow accumulates, and glaciation begins.

Question 17

Post-glacial sea level change

Answer 17

There was absolute seal level rise due to melting water and expansion of water volume due to temperature rise

Question 18

What are the 4 factors contributing to relative post-glacial sea level change?

Answer 18

1. Isostatic submergence
2. Tectonic subsidence
3. Tectonic rise
4. Sedimentation rise

Question 19

isostatic submergence

Answer 19

1st: ice sheet pressure
Locally the ice presses down land masses, while further away it pushes up landmasses

2nd: ice sheet melting
Locally the landmasses lift up, this is called isostatic rebound. Further away the landsmasses sink, this is called isostatic submergence.

Question 20

What is the effect of the isostatic rebound?

Answer 20

Relatively, the sea level rises more slowly

Question 21

What is the effect of isostatic submergence?

Answer 21

Relatively, the sea level rises faster.

Question 22

paleo rhine

Answer 22

Ice Age low sea level → Rhine flows across exposed North Sea → sea level rise floods it → Paleo-Rhine disappears.