Week 7: How to Build a Planet The Proterozoic Earth Flashcards
What is the upper and lower ages of the boundaries to the Proterozoic?
2420Ma - 541Ma
What proportion of Earth history does the Proterozoic represent?
almost half
What key events took place during the Proterozoic?
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.
What is the composition of the modern atmosphere?
Nitrogen (78%) Oxygen (21%) Argon (1%)
How does the Earth’s atmosphere compare to other planetary bodies in our solar system?
our atmosphere is 21% oxygen
has got free oxygen which is not found on other planets
What is the origin of the gases other than oxygen in the atmosphere?
degassing of mantle and crust after moon forming collision
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?
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%)
How did oxygen levels change through the Proterozoic? What caused the buildup of oxygen in the atmosphere?
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.
When did the Great Oxidation Event occur and what are some of the phenomena that indicate that it took place?
2350Ma,
evidence:
-distribution of BIFs
-red beds, detrital sedimentary rocks containing Fe3+, oxide cements that appear in 2.3ga
What was the nature of the atmosphere before the GOE and what is the evidence of no free oxygen?
-the atmosphere contained CO2 and methane with no free oxygen
- evidence for the lack of oxygen is the lack of oxidised minerals
When did the ozone layer form? What does the ozone layer protect the Earth from?
2316Ma
ozone layer= high conc of ozone in stratosphere
protects life on Earth from harmful UV rays from the sun.
What are the possible causes of the Neoproterozoic oxygenation event (NEO)?
volcanoes changing in chemical composition, p;roducing H2O instead of CO2
What is a supercontinent?
continent that includes all existing continents
What is the supercontinent cycle? What events (and evidence) are associated with continental break up and assembly of the supercontinents?
assembly and breakup are episodic. Events associated are orogeny (mountain building) and Wilson cycle (plate tectonics)
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?
orogeny is a mountain building event, it occurs in ocean - continental crust
continental - continental (most intense)
What is a Large Igneous Province (LIP) and how do their emplacement relate to the supercontinent cycle?
Large accumulation of igneous rocks
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?
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)
What is the nature of the relationship between supercontinent formation, global sea level and global climate?
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
What evidence from the rock record can be used to indicate the nature of ancient climates?
What is meant by the term ‘snowball ‘Earth? What is the evidence for glaciation at the equator?
the earths surface becomes partially or entirely frozen, glaciation/ice age occurs
What is the age of the oldest (Palaeoproterozoic) glaciogenic deposits and the key causes of that glaciation?
2420-2220ma)
huronian glaciation which was caused by oxgen reacting with methane to form CO2
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?
720-635ma
series of glaciation events caused by reduced levels of greenhouse gases and changes in tectonics
fluctuation between warmer/milder conditions and glaciation
How has the length of the day and the distance between the Earth and the Moon changed through geological time?
the length of the day and the distance between the earth and moon are both increasing very slowly
What are the key differences in tectonics between the early Precambrian and Proterozoic?
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
How did the NEO, break up of Rodinia and warming climate affect the evolution of life?
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
