Chemical evolution of the atmosphere Flashcards
What are the intersecting spheres?
- Atmosphere
- Hydrosphere (+cryosphere)
- Lithosphere
Equals:
- Antrhosphere
- Biosphere
What is the lithosphere?
The lithosphere is where the rock cycle brings rocks to the surface: controlling landforms, shaping environmental conditions, and the availability of chemicals (minerals) which weather out of those rocks.
Contains:
Geology, soil science, physical geography, natural hazards.
What is the atmosphere?
The atmosphere rapidly transports heat and water, hence fundamentally controls the climate, shapes landscapes.
Contains:
climate
What is the hydrosphere?
The hydrosphere (including cryosphere) is where water is essential to life, it is a powerful agent for weathering, shapes landforms, transports minerals and energy around the planet.
Contains:
Hydrology, glaciology, oceanography.
What is the biosphere?
The biosphere interacts with all the spheres: ecology is intricately linked to the environment but can change it also (e.g. atmospheric composition is fundamentally shaped life, human impact).
Contains:
Bio9geo) sciences, evolution, fossil records, evolution.
What is the anthroposphere?
This is not an actual sphere. However, it is human society shaped by and (now) fundamentally shaping all of the other spheres.
Contains:
Human geography, environmental science.
What type of core and crust does Earth have?
Dense elements (Fe, Ni) sunk into the interior and composes the core.
The crust is made from silicates. Silicates already contain oxygen which is why volcanoes produce oxidised gases (CO2 and SO2) instead of reduced gases.
In what eon is their the first evidence of life?
Archaean (4-2.5Ga).
Around 3.5-3.4Ga there is first fossil evidence of life. Sulfur metabolism and photosynthesis may have begun this early.
However, O2 does not accumulate during this period as there is too much to react within anoxic seas (rocks, metal ions, etc).
What happened during the proterozoic eon?
- Anaerobic, sulfate-reducing, photosynthesis occurred.
By 2.5Ga, most O2 sinks are depleted and atmospheric oxygen levels rise rapidly, until stabilising at around 10% about 1.85Ga,
There was huge precipitates of Fe from dissolved iron (banded iron formations).
In what eon did oxygen levels in the atmosphere increase rapidly and stabilised?
Proterozoic (2.5-0.542Ga)
Oceans became oxic near the surface and near-surface anaerobic bacteria all killed (mass extinction). But this gave AEROBIC bacteria abundant opportunities.
Note: anaerobic bacteria does not need oxygen to survive, but aerobic bacteria does.
In what eon was there no CH4 production and instead lots of CH4 removal?
Proterozoic (2.5-0.542Ga)
Since methane is a strong atmospheric gas, there was a catastrophic fall in temperatures (aided by a weaker young sun).
- Much of photosynthesis life died off.
In what eon does oxygen in the atmosphere form the ozone (O3) which absorbs UV radiation to provide a shield from damaging high-energy photons.
Proterozoic (2.5-0.542Ga)
By 0.85Ga, the O2 buffering system couldn’t keep up. O2 levels begun to climb again making it an ideal environment for aerobic organisms.
In what eon did the first land plant appear?
Phanerozoic (0.542Ga-present).
They first appeared around 500Ma.
O2 peaked at 30% around 400Ma allowing supergiant organisms to form (e.g. massive dragonflies).
In what period(s) had the largest mass extinction in Earth’s history?
Permian/Triassic extinction 251Ma.
What some other important facts that occurred in the phanerozoic eon?
Permian/Triassic extinction 251Ma.
Major volcanism in Siberia - huge CO2 release and other compounds (S, F, Cl).
O2 drops from 30% to 12%. CO2 increases peaking at 2000ppm (400ppm today).
By 228Ma (first dinosaurs), O2 returns to 15%. By 100Ma (first mammals, birds), O2 stabilises around 18-23% since then.
