Lecture 4&5 Planetary Biogeochemistry in Climate Regulation

When did life begin?

In the Precambrian Era 3.5 billion years ago

What happend in the Precambrian Era?

• 4,600 - 590 mya

• Mostly unicellular organisms

• Absence of O₂

• Anaerobic metabolism

• Very high CO₂

What was the Paleozoic Era?

• 590-250 mya

• Life forms adapted to land (395 mya)

When was the first mass extinction event?

• 65 mya

• Cleared way for the rise of mammals

When did cyanobacteria develop?

• cya. 3 billion years ago

• Performed oxygenic photosynthesis

• Lack of predators and large amounts of CO2 allowed it to thrive

Why is oxygen photosynthesis important?

• Organisms take up CO2 to make organic carbon and produce O2 in the process

• Removes CO2 from the atmosphere and adds O2 to the atmosphere

• Led to life evolving

What happens to cyanobacterial biomass when they die off?

Become buried in the seabed and lock away CO2

What is the Great Oxidation Event?

A significant rise in atmospheric O2, around 2.3 bya (billion years ago)

What did the elevated O2 content allow?

Evolution of aerobic metabolism, which produces more energy than anaerobic metabolism, led to an explosion in the diversity of life and gigantism (bigger organisms/mammals) - 200 mya

What eventually engulfed cyanobacteria?

Chloroplasts (descendants), were not detroyed

What makes up the modern day atmospheric concentration?

• Nitrogen 78%

• Oxygen 21%

• Argon 0.9%

• Trace gasses (incl Carbon Dioxide) 0.1%

Which greenhouse gas is stronger than CO2?

Methane, despite low concentration (0.442%)

Global Warming Potentials (GWP)

How much heat a gas will trap over a given period of time relative to the same amount of carbon dioxide

Microbial methane production

• Organism: Methanogens

• Condition: Anoxic (absence of oxygen), e.g. archaea produce it through the reduction of carbon dioxide - uses hydrogen in the reduction process to generate energy

• Anoxic conditions, as enzymes are sensitive to oxygen, and the pathways would be reversed

• Omitted from methanogenic organisms

What are the pathways in which methane can be created?

1. Hydrogenotrophic

2. Methylotrophic

3. Acetoclastic

What is methane?

Organic compound, used as “fuel” by organisms

What are Methanotrophs?

Use methane oxidation under oxic conditions to produce energy, which reduces the net amount ommitted, but requires oxygen

What are the other natural sources of atmospheric methane?

• Wetlands: tropics (warmer conditions), Northern latitude, and other

• Termites

• Ocean

• Freshwater

• Geological

• Ruminants from cows

Why are termites producers of methane?

• Gut is an ‘organic’ rich and oxygen poor environment

• Break down wood and need microorganisms in their gut to do this

• Then microorganisms can convert the organic carbon into methane

What are some anthropogenic sources of atmospheric methane?

• Coal mines

• Natural gas

• Petroleum industry

• Animal waste

• Landfills

• Rice paddies - anoxic conditions

• Enteric fermentation

What about sinks of methane?

• Reaction with OH

• Removal by stratosphere

• Removal by soils

Through chemical reactions that take place, overall atmospheric increase of methane

What else does biological productivity need other than carbon?

Phosphorus and Nitrogen (Redfield Ratio)

What is phosphorous for?

DNA, RNA, ATP, cell membranes (phospholipids)

Phosphorous cycle

• Tide up in marine sediments

• Humans interact through mining for fertilisers

• Key limiting nutrient, not evenly distributed

• Slow cycle influenced by human activities

What are the anthropogenic phosphorus inputs into the ocean?

Phosphorus may run out in 1000 years from mining sources

• Sewage

• Fertiliser

• Deforestation + soil loss

What will happen to the marine ecosystem when phosphorus runs out?

Reduced productivity

Nitrogen cycle

• Abundant in the atmosphere

• Influenced by fertiliser use

• Biological fixation

• Nitrogen gas converted into ammonium

• Needed by plants

• Transported by river flow

• Organisms convert N2 → NH3

• Plants need NH4+ or NO3-

How do we produce nitrogen fertilisers?

Nature: Nitrogen-fixing organisms convert nitrogen gas to ammonia (Nitrogen fixation by diazotrophs)

Industry: Haber-Bosch process (Nitrogen gas → ammonia = base of fertiliser)

How do carbon, nitrogen and phosphorous effect the climate?

• Influence primary productivity

• Nitrogenous compounds impact climate warming

• How phosphorus and nitrogen cycles respond to climate change is unclear