Ia Chapter 2 A Habitable World

Question 1

What does a habitable planet require?

Answer 1

-oxygen rich atmosphere
-oceans

Question 2

What is a circumstellar habitable zone?

Answer 2

This is the range of distances from a star for which liquid water can exist on a planetary surface.

Question 3

Planet effective temperature equation

Answer 3

Te^4 = L / (4πR^2 x (5.67x10^-8))

Where L is the total power radiated by the plant in watts, R is the radius of the planet in m.

Question 4

Solar flux density equation (energy received per square meter by a planet)

Answer 4

Ein = luminosity / 4πa^2

Where a is the distance of the planet from the star.

Question 5

What is a continuous habitable zone?

Answer 5

This is a region in which a planet may retain liquid water and reside for most of a stars life.

Question 6

What effect do the greenhouse effect and planetary albedo have on the habitable zone?

Answer 6

The greenhouse effect cause a planet to heat up, extending the habitable zone out.

Planetary albedo reflects energy from the planet, causing the habitable zone to extend inwards.

Question 7

Major CO2 sources

Answer 7

• decarbonation (destruction of calcium carbonate to form CO2 etc.)
• volcanic outgassing

Question 8

Major CO2 sinks

Answer 8

• dissolved in rainwater to chemical weather rocks forming CaCO3.

-photosynthesis.

Question 9

What factors of a star affect the habitable zone location?

Answer 9

The mass of the star and the stars luminosity both affect if a star can develop a planetary system capable of sustaining life.

Question 10

What can the mass of a star be in a life sustaining system?

Answer 10

The star has to be larger than 0.5 solar masses. If the star is smaller then planets will have to be so close they will become tidally locked.

The star has to be smaller than 1.5 solar masses otherwise the lifespan of the star is too short to develop a planetary system and for complex life to evolve.

Question 11

What is tidal locking?

Answer 11

This is when a planets rotational period synchronises with its orbital period.

Question 12

What are the two stable orbital types around binary star systems?

Answer 12

Close binaries - the planet orbits around both stars.

Wide binaries - the planet orbits around one star.

Question 13

What is a galactic habitable zone?

Answer 13

This suggests that certain regions of the galaxy are more habitable than others. The sun is near the edge of the milky was, so is subjected to less radiation and gravitational effects from the higher volumes of stars near the centre.

Question 14

How do we know early Earth contained liquid water?

Answer 14

Rocks as old as 3.8 Ga contain sedimentary rock such as limestone which formed by calcium carbonate precipitating out in water and lavas form as pillow lavas which occur when the lava is cooled underwater.

Question 15

What three processes transfer heat from the interior of the planet to the surface?

Answer 15

• Conduction
• Convection
• Advection (occurs when hot magma rises)

Question 16

What evidence do we have of a snowball earth?

Answer 16

Sedimentary rocks formed 750 - 580 Ma years ago near the equator have layers of glacial deposits interspersed with layers of iron rich rock and layers of carbonate rock which typically forms in tropical environments.

Question 17

Why would iron rich rocks be interspersed with glacial deposits?

Answer 17

When the planet froze the atmosphere would be CO2 rich and O2 would be at low concentrations. This would allow Fe to dissolve in the water.

When Earth started to heat up the atmosphere would become O2 rich allowing the Fe to precipitate out ontop of the glacial deposits.

Question 18

Why would the atmosphere during snowball earth become CO2 rich?

Answer 18

When the Earth froze volcanic outgassing of CO2 would still occur. As there world be no rain to remove the CO2 from the atmosphere the atmosphere would accumulate up to 350 times present day levels of CO2.

Question 19

What could cause “snowball Earth” to rapidly heat up?

Answer 19

The atmosphere would have been heavily concentrated with CO2 which is a greenhouse gas. This would cause the Earth to rapidly warm and the ice to melt in perhaps le as a few as hundred years.

Question 20

What happened to life during snowball earth?

Answer 20

The conditions during snowball earth would have been extremely harsh and likely killed many of the single cell organisms.

Life may have survived around hydrothermal vents or as photosynthesising cells on top of ice sheets.

All life currently on Earth evolved from the surviving organisms.

Question 21

What evidence suggest that most of the water on Earth is not from comets?

Answer 21

The ratio of two stable isotopes of hydrogen found in comets differs largely from the ratio of hydrogen isotopes found on earth. This implies most of earths water is not from comets.

Question 22

Why is it unlikely Earth scavenged volatiles direct from the solar nebula?

Answer 22

The relative concentrations of the noble gasses were much higher in the solar nebula than are found here on earth, and it is unlikely earth could lose these gasses without losing other volatiles.

Question 23

Where could earths water come from if not comets?

Answer 23

Water could have been incorporated into the forming earth as hydrated minerals which them would have undergone degassing, forming water.

Question 24

In the first billion years, how much H2O was present in earths atmosphere?

Answer 24

There would have only been trace amounts of H2O caused by the the breakdown of water vapour by UV radiation.

Question 25

What would had been the dominant constituents of Earths early atmosphere?

Answer 25

Nitrogen, carbon dioxide, possibly sulfur oxide and water vapour.

Question 26

How may oxygen have been formed on Earth?

Answer 26

It may have been produced by photosynthesising Cyanobacteria in the archaean era (3.8 Ga - 2.5 Ga ago).

Question 27

How do we know the atmosphere became more oxygen rich during the archaean period?

Answer 27

Layers of iron rich rock around 3. 8 - 2.5 Ga years old suggest the atmosphere became more oxygen rich causing iron to oxidise and precipitate out the water.

Question 28

What is a BIF?

Answer 28

Banded iron formation

Question 29

How was iron injected into the early ocean?

Answer 29

In anoxic deep sea hydrothermal vents, iron containing minerals may have dissolved in the seawater as it was in a reduced form and was infected injected by hydrothermal vents.

Question 30

How did iron get from the deep sea to shallow water?

Answer 30

One idea suggests iron was consumed by bacteria near the vents which were then swept to shallower water as large colony's. Once in shallow water they died and decomposed where the iron became oxidised near the surface and precipitated out, forming a thin layer.

Question 31

What palaeontological and geochemical evidence is there for early life on earth?

Answer 31

Palaeontological and carbon isotopic data obtained from the preserved geological rock record. This data suggests life may have started between 3.8-4.3 Ga ago.

Question 32

What are **Stromatolites**?

Answer 32

These are mound shaped structures that are built up by the accumulation of sediments that consist of thin gelatinous mats alternating with thin layers of calcium carbonate. Fossilised stromatolites may indicate life as early as 3.46 Ga ago. They potentially display microfossils similar to modern Cyanobacteria, although this is disputed.

Question 33

How can carbon be used as an indicator of biological processes?

Answer 33

Biological process prefer to use C12 isotopes as they require less energy to form bonds than C13. By comparing the ratio of C12 to C13 to that of the ratio found in carbonate rock you can deduce if it was formed by biological processes.

Question 34

Standard carbon ratio equation

Answer 34

delta C13 = [((C13/C12 ratio of sample) / (C13/C12 ratio of standard)) -1] x1000 This provides the Delta C13 value in terms of parts per thousand (%o).

Question 35

Where does the largest isotopic fractionation occur?

Answer 35

Autotrophs are responsible for causing the isotopic fractionation as they fix more C12 from the atmosphere before being consumed and passing the C12 up the food chain.

Question 36

What is **kerogen**?

Answer 36

These are macromolecular molecules that refers to the organic matter present in sediments. The ratio of carbon isotopes in **kerogen** can be used to unravel the biochemistry of the ancient Earth.

Question 37

What is an **methanotroph**?

Answer 37

This is an organism that can use methane as a nutrient.

Question 38

What are the three original groups of the phylogenetic tree?

Answer 38

**Eukaryotes** - single celled organisms that contain a nucleus. **Prokaryotes** - single celled organisms that lack a nucleus and other organelles like bacteria. **Archaea** - these lack a nucleus, but share some of the genetics of eukaryotes. Some of there genetics are unshared.

Question 39

How can temperature extremes affect cells?

Answer 39

Below 0 ice crystals can cause the structural breakdown of cells. High temperatures can also cause the structural beak down of cells as well as causing proteins and nucleic acids to denature. It can increase the rate which material diffuses across the cell membrane of cause the membrane to fail at temperatures above 100 degrees.

Question 40

What traits allow hyperthermophiles to live at high temperatures.

Answer 40

- Different ratios of lipids in cell membranes to reduce fluidity. - proteins that can cope with higher temperatures better. - DNA has elevated G+C to A+T or A+U ratios. G+C is more thermally stable due to extra hydrogen bond.

Question 41

What traits allow phychrophiles to live at high temperatures.

Answer 41

- Different ratios of lipids in cell membranes to improve fluidity. - Accumulate solulable compounds to reduce the freezing point. - Create molecules such as glycerol which can act as antifreeze agents. (**thermal hysteresis**)

Question 42

What is **thermal hysteresis**/

Answer 42

A process that depresses the freezing point of water well below its melting point by allowing proteins to bind to the edge of ice crystals preventing the addition of further water molecules.

Question 43

How can some organisms withstand ionising radiation.

Answer 43

Some organisms have evolved the ability to rebuild DNA from radiation damaged fragments in the absence of an intact template.

Question 44

How to some organisms cope with acidic/alkali environments?

Answer 44

They maintain neutrality inside their cells to prevent the acidic/alkali conditions from damaging internal molecules and processes.

Question 45

How do organisms deal with environments of high salinity?

Answer 45

Organisms in high saline environments could suffer from dehydration due to osmosis. To combat this my they produce large amounts of internal solute or by retaining a solute that was extracted outside the cell.

Question 46

How do some organisms survive **desiccation **?

Answer 46

Some organisms survive desiccation by entering a state of apparent suspended animation known as **anhydrobiosis**. This is characterized by little intracellular water and no metabolic activity.

Question 47

How do organisms deal with increased pressure?

Answer 47

They have often adapted the compositions of their cell membranes to increase fluidity.

Question 48

How do organisms deal with high oxygen environments?

Answer 48

Oxygen causes oxidative reactions, which can damage organism. Some organisms avoid or repair this damage using antioxidants. Respiration is more efficient than on anaerobic metabolism.

Question 49

Examples of extreme environments.

Answer 49

- Hot springs - the deep sea - hydrothermal vents - salt flats, evaporation ponds and natural lakes - evaporites - deserts - the atmosphere - ice permafrost and snow - sub surface

Question 50

What elements does Mars atmosphere consist of?

Answer 50

CO2, N2, Ar, O2, CO, H2O, Ne, Kr, Xe, O3, NO, CH4

Question 51

What similarities does Mars have to earth?

Answer 51

- Contains an atmosphere - axial tilt - seasons - water (mostly ice) - in suns habitable zone

Question 52

What factors make Mars uninhabitable?

Answer 52

- No magnetic field (not protection from solar winds) - extreme thin atmosphere - no liquid water - extreme exposure to UV radiation - extreme surface temperature fluctuations - low surface temperature

Question 53

What evidence do we have that Mars may have once been habitable?

Answer 53

- past fluvial processes suggest liquid water existed on the surface. - volcanoes suggest previous tectonic action. Manage and had a magnetic field.

Question 54

How does mars' axial tilt affect atmosphere density?

Answer 54

As the tilt has ranged from 5° to 35° it charges how much the polar ice sheets melt. Smaller angles mean that polar ice caps are better shielded from the sun year round, so can maintain CO2 ice year round. Larger angles subject the ice caps to more sun, meaning more ice melts adding more CO2 to the atmosphere.

Question 55

What is **Radar**?

Answer 55

Radar is a form of technology that can be used to remotely map a landscape. Cm or mm microwaves are produced and directed at a planets surface. The microwaves can pass through cloud and atmosphere, but are reflected by solid and liquid surfaces. By measuring now long it takes for a microwave to be rebounded you can create an image of a planet surface. Sometimes its microwaves can be reflected by different layers in ground and ice providing information about rock formation and structure.