Earth Systems 1000 Topic 9

How many stages can Earth be considered to have of atmospheric evolution

1. Proto-atmosphere

2. First atmosphere

3. Second atmosphere

4. Third atmosphere

5. Modern atmosphere

What is Earth’s proto-atmosphere

It is the stage following earths accretion and would have had an early atmosphere rich in He and H2 molecules

What would happen to heat within earth

The heat would have resulted in the He and H2 molecules to move rapidly and reach a velocity. While the remaining molecules would have been stripped by solar winds

What would happen during earths first atmosphere

The earths proto-atmosphere He and H2 was removed, it was gradually replaced with volcanic and cometary/meteoritic gasses making it richer in CO2, H2O, N2, NH3, and CH4

What are volcanic gases made of

Roughly 70-90% H2O with the remaining being C-S-N gasses

What would release volatiles trapped in minerals as gases emanating from volcanoes

After differentiation of the inner earth into core and mantle, melting of the mantle would release volatiles due to temperature and pressure

What is another way that some gasses would have been delivered

By comets and carbonaceous chondrites meteorites

The differentiation of the Earth to have a core would allow…

The formation of a magnetic field that helped shield the Earth from solar winds and aid with retaining light gasses in the atmosphere

During the earths second atmosphere what did the atmosphere change from

It gradually evolved to one dominated by N2 and CO2 as the H2O and NH3 levels dropped

Why would the atmospheric H2O lower

It would have lowered as the surface cooled sufficiently to allow stable liquid water (oceans, lakes, streams, groundwater)

What would atmospheric NH3 do to UV

It would’ve lowered as UV rays spilt it into molecules of hydrogen (forming H2) and nitrogen (forming N2)

Why can H2 escape into space easier than N2

H2 is lightweight and can more easily escape into space from Earths gravitational pull whereas N2 is unreactive and stable and able to accumulate in the atmosphere

What happens during the evolution of Earths second atmosphere and into the third

CO2 also transitioned from a major gas to one present only in trace amounts

How much CO2 is found in mars and Venus atmosphere

Mars : 95%

Venus : 96%

What happens as liquid becomes stable at the surface during earths second atmosphere

CO2 could dissolve in water from carbonate and bicarbonate ions, which could react with Ca2+ to form carbonate

Why is CO2 important

Due to greenhouse gas properties that retain heat in the atmosphere making the surface habitable in terms of temperature

What does earths third atmosphere mainly resulted from

It’s evolving biosphere, including the evolution of oxygenic photosynthesis, it has N2 and trace O2

What did Cyanobacteria eventually evolve

The ability to produce O2 and organic C molecules from CO2 and light energy; e allowing the release of O2 into the atmosphere

When did O2 accumulate in the atmosphere

It did not start to accumulate in the atmosphere until ca. 2.3 Ga

What is also a byproduct of the biosphere

N2 is a byproduct of the biosphere

What dominated life on the early earth

Cyanobacteria

What evidence can be found that Cyanobacteria dominated life on the early earth

The form of stromatolites - mound-shaped accumulations of microbial layers that became fossilized

What is the Great Oxidation Event (GOE)

It is geological evidence for the first accumulation of atmospheric O2 at ca. 2.3 Ga in earths iron

What the earths modern atmosphere

0.8 Ga - present

The earths atmospheric O2 remained at or near levels 1% of the present

What happened after 0.8 Ga

O2 started to accumulate to near-modern levels at roughly the time that complex multicellular life evolved

What happened throughout Phanerzonic

The O2 was variable but constrained between ~15% and 35% with current levels at 21%

This evidence comes from ancient charcoal and the presence of giant insects

Why is oxygenating earth’s atmosphere

To allow complex multicellular organisms to breathe and evolve, but also to allow the formation of an ozone layer

How does the ozone (O3) form

In a 2 step reaction in the atmosphere ~30km above the surface

1. O2 + soler energy

2. O2 + O

Why is the presence of O3 in the stratosphere important

It filters out harmful UV light from reaching the surface

What is the earths modern atmospheric composition

Nitrogen = 78.08% (78.00%)

Oxygen = 20.95% (21.00%)

Other gasses = 0.97% (1.00%)

Where can aerosol be kept

It can be kept aloft in the atmosphere

What is air pressure and how is it measured

It pushes that air that exerts on its surroundings

It is measured in units called atmospheres (atm) or bars

What is air density and how does it change the weight of the air

It is the total mass of gas molecules per unit of volume

The weight of air at higher elevation compresses air at lower elevations increasing towards the surface

Where is 99% of the atmospheres gases found

Below an elevation of 50km

What happens in high atmosphere

There are very few interactions of gas molecules with each other

What is heat

It is a form of energy. All substances are made of atoms or molecules that are in motion and have kinetic energy. It is defines as the total kinetic energy of all atoms/molecules in a substance

What is temperature

It is measured as the average kinetic energy of individual atoms/molecules in a substance. The faster atoms/molecules vibrate (or move), the higher the temperature

How is heat and temperature related

If heat energy is added to a substance, atoms move faster and the temperature increases

If heat energy is removed from a substance, atoms move slower and temperature decreases

How is heat energy transferred

Radiation

Conduction

Convection

What is radiation

A form of energy transported by electromagnetic waves that does not require a medium to transfer. It is the most important heat transfer for the atmosphere

What is convection

The transfer of heat through matter through molecular collisions, with heat transferred from higher T to lower T. Air is a conductor and the least important for the atmosphere

What is convection

The transfer of heat by mass movement or circulation in a substance. It is important for global heat transfer