Lecture 6: Faint Young Sun Puzzle Flashcards
What is the goldilocks problem?
There are three planets in which life could have existed but there are aspects of two that mean they are not suitable for life while the other is
Describe why mars is not suitable for life
It is very cold (-90 Celsius), very dry, smaller mass and therefore gravity to retain important gases and volatiles
Describe why venus is not suitable for life
Runaway greenhouse effect previously; meaning very hot, no water, splitting up of elements (shown by surrounding clouds). Clouds mean high atmospheric albedo and insulation
Are we confident that all three planets would have contained water at some point? What happened to the water on venus and mars?
Yes - venus evaporated it, mars got too cold
What is the habitable zone?
A relatively narrow zone in which water and life can exist.
What can the surface temperatures range between in the habitable zone?
0-70 Celsius
Why is it not possible to say that all we need on a planet is water?
Because then we could extend the surface temperatures to 100 Celsius but between there and 70 Celsius evaporation would causes oceans to disappear eventually. There would also be too many water vapour clouds that would increase greenhouse effect too much
Is the habitable zone fixed?
No - it change with changes in the sun’s brightness and size
What is the stellar evolution/main sequence?
The process of star evolution
What is the initial phase of the main sequence and what effect does it have?
Burning hydrogen and helium together at the core. This acts as a fuel and the more that gets burnt the greater the capacity to continue burning.
What happens to the star as it continues to burn more and more hydrogen at a faster rate?
It eventually becomes ~30% brighter, grows in mass, denser and more concentrated core
Why does the star increase in mass as hydrogen and helium collide?
Because the product is a much denser element
What happens to the star as its core becomes denser and more concentrated?
Its gravity strengthens
What happens between the increased gravity and the star’s explosions?
They fight against each other which leads to an increase in its power.
What will happen when the star’s hydrogen fuel runs out?
The star will enter a burning out phase and transform in to a red giant where it will be much larger. It will then shed outer layers and once all nuclear fusion had ended it will collapse under its own gravity to become a cooler “white dwarf”.
What does the Herzprung-Russell diagram represent?
How a star’s temperature and luminosity change as the star evolves.
Why are we mostly interested in the star’s luminosity?
It is the measure of the flux of radiation that is coming out of it and therefore reaches different planets
Describe how the sun’s luminosity has been increasing since the creation of the earth
positive non-linear. This is because the nuclear fusion of hydrogen speeds itself up so that burning takes place faster
How much dimmer do we estimate the sun was before? What does this suggest the climate of the earth used to be like but wasn’t?
30% - it might have been cooler but it wasn’t
What evidence is there that the earth’s climate used t be the same as it was now and not ridiculously cold?
the presence of life that was found and liquid water
What is one theory that is wrong for why the earth was able to keep warm during the time of a dimmer sun?
The earth was darker and so could absorb and retain more heat
What is the greenhouse effect?
Greenhouse gases absorb the reemitted energy from the surface of the earth in the appropriate wavelength and then get excited by this energy whereby they then reemit it back toward the earth. This then causes the earth’s atmosphere to warm up
What is the atmospheric window?
Energy reemitted from the earth in a specific wavelength that greenhouse gases are not able to absorb so it passes through the atmosphere
What is a better name for the greenhouse effect and why?
greenhouses are not warm for the same reason so it is better to call it the blanket effect
How is most surface carbon balanced?
It is transported in the ground over ~100,000 year processes in to the crust molecules or as carbonate molecules
How many carbon molecules are stored in organic form and how many are stored as carbonate?
Organic form: 1.25x10^21
Carbonate form: 5x10^21
How long can carbon be stored underground compared to at the surface?
Underground: 2.5x10^8 years
Surface: 1.28x10^5 years
What are the three ways that carbon is released from the underground?
Volcanic degassing, plate margins, weathering of sedimentary rocks
What is silicate weathering?
Main removal process of carbon dioxide from the atmosphere which involves weathering rock in the crust without carbon but with calcium and magnesium that reach with the atmospheric carbon to form carbonates
What happens to the carbonate rocks produced in silicate weathering over time?
They become sedimentary rocks where the carbon is then stored underground.
What can the silicate weathering process also produce?
Calcium and magnesium solutions that react with atmospheric carbon dioxide via rainwater to make a weak acid solution
What can happen to the weak acid solutions produced in silicate weathering?
Some organisms react with them to then precipitate carbonates that sink to the ocean floor and form part of it. This then means they are stored underground below the ocean
So, what are the two forms of silicate weathering that regulate carbon?
Ocean organisms with acid solutions and weathering of sedimentary rocks
What is the crucial feedback within the silicate weathering process that allows it to regulate climate?
When temperature increases, silicate weathering increases and so does the absorption of carbon. This means that the greenhouse gas layer thins. So when solar luminosity increases, the expected temperature increase will be counteracted by increased silicate weathering
How do plants/life also contribute to the increased silicate weathering?
Temperature increase will increase biosphere productivity. the biosphere wants to break up rocks to extract nutrients it needs which in turn exposes other elements within them to atmospheric carbon dioxide which it can react with together to form carbonates.
What will happen if too much carbon is extracted from the atmosphere?
It will cool the planet which will damage the biosphere and its ability to remove carbon. This will allow carbon to build up which will thicken the GHG layer leading to warming again -yay!
What are the levels of carbon in the atmosphere which are insufficient for most plant life? What levels of carbon in the atmosphere can some plants go down to?
Most plants: 150ppm
Some: 10ppm
What did the atmospheric carbon level go down to in the last ice age/ glacial maximum? and what is it today?
last ice age: 180ppm
today: >440ppm
