Week 7: How to Build a Planet The Proterozoic Earth

Question 1

What is the upper and lower ages of the boundaries to the Proterozoic?

Answer 1

2420Ma - 541Ma

Question 2

What proportion of Earth history does the Proterozoic represent?

Answer 2

almost half

Question 3

What key events took place during the Proterozoic?

Answer 3

1) Modern plate tectonics became active.

2) Ancient cores of the continents moved over wide areas of the globe, accumulating smaller fragments of crust.

3) The temperature of Earth significantly cooled.

Question 4

What is the composition of the modern atmosphere?

Answer 4

Nitrogen (78%) Oxygen (21%) Argon (1%)

Question 5

How does the Earth’s atmosphere compare to other planetary bodies in our solar system?

Answer 5

our atmosphere is 21% oxygen
has got free oxygen which is not found on other planets

Question 6

What is the origin of the gases other than oxygen in the atmosphere?

Answer 6

degassing of mantle and crust after moon forming collision

Question 7

How is oxygen added to and removed from the Earth’s atmosphere? What is the most important source of
oxygen today? What are the major balancing mechanisms today?

Answer 7

When fossil carbon sources are combusted, it reacts with atmospheric molecular oxygen to create carbon dioxide. Photosynthesis from plants reintroduces oxygen into the atmosphere.

most important source= the ocean (about 50%)

Question 8

How did oxygen levels change through the Proterozoic? What caused the buildup of oxygen in the atmosphere?

Answer 8

oxygen levels increased to about 50% of the present value. Build-up caused by new sources of oxygen as a result of biological activity and loss processes becoming saturated.

Question 9

When did the Great Oxidation Event occur and what are some of the phenomena that indicate that it took place?

Answer 9

2350Ma,
evidence:
-distribution of BIFs
-red beds, detrital sedimentary rocks containing Fe3+, oxide cements that appear in 2.3ga

Question 10

What was the nature of the atmosphere before the GOE and what is the evidence of no free oxygen?

Answer 10

-the atmosphere contained CO2 and methane with no free oxygen

• evidence for the lack of oxygen is the lack of oxidised minerals

Question 11

When did the ozone layer form? What does the ozone layer protect the Earth from?

Answer 11

2316Ma
ozone layer= high conc of ozone in stratosphere
protects life on Earth from harmful UV rays from the sun.

Question 12

What are the possible causes of the Neoproterozoic oxygenation event (NEO)?

Answer 12

volcanoes changing in chemical composition, p;roducing H2O instead of CO2

Question 13

What is a supercontinent?

Answer 13

continent that includes all existing continents

Question 14

What is the supercontinent cycle? What events (and evidence) are associated with continental break up and assembly of the supercontinents?

Answer 14

assembly and breakup are episodic. Events associated are orogeny (mountain building) and Wilson cycle (plate tectonics)

Question 15

What is an orogeny? In which plate tectonic settings do the most intense orogenesis occur? Present day orogens are identified by finding regions of high, rugged peaks. How can geologists identify orogens that have been eroded away?

Answer 15

orogeny is a mountain building event, it occurs in ocean - continental crust
continental - continental (most intense)

Question 16

What is a Large Igneous Province (LIP) and how do their emplacement relate to the supercontinent cycle?

Answer 16

Large accumulation of igneous rocks

Question 17

What are the names of the Proterozoic supercontinents and the approximate ages of their formation and break up? When did the Grenville Orogeny occur and the assembly of which supercontinent is it associated with? When
did the Iapetus Ocean open?

Answer 17

1, Initial assembly of Columbia (2000-1800ma)
2. Break up of Columbia (1500ma)
3. Formation of Rodinia (1100-850ma)
-the grenville orogeny was assoaciated with the formation of Rodinia
4. Break up of Rodinia (825-720ma)
-The Iapetus Ocean opened during the breakup of the supercontinent Rodinia (700-550ma)
5. Formation of Pannotia (630ma)
6. Break up of Pannotia (600-580ma)

Question 18

What is the nature of the relationship between supercontinent formation, global sea level and global climate?

Answer 18

long length mid-ocean ridges when the continents are broken up displaces ocean volume on to the continents, thereby contributing to high sea levels.

High sea levels mean large areas of shallow marine shelves, and hence an enhanced volume and diversity of biotically favourable environments

Question 19

What evidence from the rock record can be used to indicate the nature of ancient climates?

Question 20

What is meant by the term ‘snowball ‘Earth? What is the evidence for glaciation at the equator?

Answer 20

the earths surface becomes partially or entirely frozen, glaciation/ice age occurs

Question 21

What is the age of the oldest (Palaeoproterozoic) glaciogenic deposits and the key causes of that glaciation?

Answer 21

2420-2220ma)
huronian glaciation which was caused by oxgen reacting with methane to form CO2

Question 22

What is the age of the extended glacial event that occurred at the end of the Proterozoic and the key causes of that glaciation? Is it a single event or a series of events? What was the nature of the climate between the glacial periods?

Answer 22

720-635ma
series of glaciation events caused by reduced levels of greenhouse gases and changes in tectonics

fluctuation between warmer/milder conditions and glaciation

Question 23

How has the length of the day and the distance between the Earth and the Moon changed through geological time?

Answer 23

the length of the day and the distance between the earth and moon are both increasing very slowly

Question 24

What are the key differences in tectonics between the early Precambrian and Proterozoic?

Answer 24

lack of plate tectonics in the precambrian - stagnant lid tectonics, formation of first continental crust and protocontinents

in the proterozoic there was the emergence of modern plate tectonics and continental growth

Question 25

How did the NEO, break up of Rodinia and warming climate affect the evolution of life?

Answer 25

NOE = neoproterozoic oxygnetaion event leading to a sharp rise in atomspheric oxygen, this stimulated photosynthesis and increased nutrient runoff leading to the radiationn/evolution of life, paving the way for the cambrian explosion