Lecture 6: Faint Young Sun Puzzle

Question 1

What is the goldilocks problem?

Answer 1

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

Question 2

Describe why mars is not suitable for life

Answer 2

It is very cold (-90 Celsius), very dry, smaller mass and therefore gravity to retain important gases and volatiles

Question 3

Describe why venus is not suitable for life

Answer 3

Runaway greenhouse effect previously; meaning very hot, no water, splitting up of elements (shown by surrounding clouds). Clouds mean high atmospheric albedo and insulation

Question 4

Are we confident that all three planets would have contained water at some point? What happened to the water on venus and mars?

Answer 4

Yes - venus evaporated it, mars got too cold

Question 5

What is the habitable zone?

Answer 5

A relatively narrow zone in which water and life can exist.

Question 6

What can the surface temperatures range between in the habitable zone?

Answer 6

0-70 Celsius

Question 7

Why is it not possible to say that all we need on a planet is water?

Answer 7

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

Question 8

Is the habitable zone fixed?

Answer 8

No - it change with changes in the sun’s brightness and size

Question 9

What is the stellar evolution/main sequence?

Answer 9

The process of star evolution

Question 10

What is the initial phase of the main sequence and what effect does it have?

Answer 10

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.

Question 11

What happens to the star as it continues to burn more and more hydrogen at a faster rate?

Answer 11

It eventually becomes ~30% brighter, grows in mass, denser and more concentrated core

Question 12

Why does the star increase in mass as hydrogen and helium collide?

Answer 12

Because the product is a much denser element

Question 13

What happens to the star as its core becomes denser and more concentrated?

Answer 13

Its gravity strengthens

Question 14

What happens between the increased gravity and the star’s explosions?

Answer 14

They fight against each other which leads to an increase in its power.

Question 15

What will happen when the star’s hydrogen fuel runs out?

Answer 15

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”.

Question 16

What does the Herzprung-Russell diagram represent?

Answer 16

How a star’s temperature and luminosity change as the star evolves.

Question 17

Why are we mostly interested in the star’s luminosity?

Answer 17

It is the measure of the flux of radiation that is coming out of it and therefore reaches different planets

Question 18

Describe how the sun’s luminosity has been increasing since the creation of the earth

Answer 18

positive non-linear. This is because the nuclear fusion of hydrogen speeds itself up so that burning takes place faster

Question 19

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?

Answer 19

30% - it might have been cooler but it wasn’t

Question 20

What evidence is there that the earth’s climate used t be the same as it was now and not ridiculously cold?

Answer 20

the presence of life that was found and liquid water

Question 21

What is one theory that is wrong for why the earth was able to keep warm during the time of a dimmer sun?

Answer 21

The earth was darker and so could absorb and retain more heat

Question 22

What is the greenhouse effect?

Answer 22

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

Question 23

What is the atmospheric window?

Answer 23

Energy reemitted from the earth in a specific wavelength that greenhouse gases are not able to absorb so it passes through the atmosphere

Question 24

What is a better name for the greenhouse effect and why?

Answer 24

greenhouses are not warm for the same reason so it is better to call it the blanket effect

Question 25

How is most surface carbon balanced?

Answer 25

It is transported in the ground over ~100,000 year processes in to the crust molecules or as carbonate molecules

Question 26

How many carbon molecules are stored in organic form and how many are stored as carbonate?

Answer 26

Organic form: 1.25x10^21

Carbonate form: 5x10^21

Question 27

How long can carbon be stored underground compared to at the surface?

Answer 27

Underground: 2.5x10^8 years
Surface: 1.28x10^5 years

Question 28

What are the three ways that carbon is released from the underground?

Answer 28

Volcanic degassing, plate margins, weathering of sedimentary rocks

Question 29

What is silicate weathering?

Answer 29

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

Question 30

What happens to the carbonate rocks produced in silicate weathering over time?

Answer 30

They become sedimentary rocks where the carbon is then stored underground.

Question 31

What can the silicate weathering process also produce?

Answer 31

Calcium and magnesium solutions that react with atmospheric carbon dioxide via rainwater to make a weak acid solution

Question 32

What can happen to the weak acid solutions produced in silicate weathering?

Answer 32

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

Question 33

So, what are the two forms of silicate weathering that regulate carbon?

Answer 33

Ocean organisms with acid solutions and weathering of sedimentary rocks

Question 34

What is the crucial feedback within the silicate weathering process that allows it to regulate climate?

Answer 34

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

Question 35

How do plants/life also contribute to the increased silicate weathering?

Answer 35

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.

Question 36

What will happen if too much carbon is extracted from the atmosphere?

Answer 36

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!

Question 37

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?

Answer 37

Most plants: 150ppm

Some: 10ppm

Question 38

What did the atmospheric carbon level go down to in the last ice age/ glacial maximum? and what is it today?

Answer 38

last ice age: 180ppm

today: >440ppm