Exobiology Flashcards
What is the Fermi Paradox?
the Fermi Paradox states that there should be a great many space-faring civilisations out there in the Universe – so why don’t we see them?
What two questions must be asked to figure out if we are alone in the universe?
1) is there life elsewhere in the solar system?
- Mars, Europa, Titan, Enceladus
2) is there life elsewhere in the Universe
- Extrasolar planets.
At present…
…n = 1
What is The Drake Equation used to figure out?
no. of civilisations in Milky Way whose transmissions are detectable
What is life?
1 – life has energy flow through it – it transforms energy into useable energy enabling it to:
move
respond to the environment
grow
reproduce
2 – life is characterised by the flow of information which enables it to:
move
respond to the environment
grow
reproduce
3 – characterised by bounded compartments in thermodynamic disequilibrium with the environment
Life is a chemical system that:
1 - Is in disequilibrium with its surroundings
2 – Has the property of replicating itself
3 – Undergoes evolutionary change over time
What two reactions are coupled in lifes chemical system?
Exergonic and endergonic reactions.
What do exergonic reactions release?
generates ATP
What do endergonic reactions use up?
uses ATP.
What codon is always the start codon?
The start codon is always AUG, which also codes for methionine. This means all amino acid sequences will contain methionine as its first amino acid.
What does the STOP codon do?
signals the end of translation
How do you translate using the genetic code grid?
1) Scan for start codon (AUG)
2) Use grid to convert codon (3 bases) into amino acids until a stop codon is reached.
What happens to codons that come before the START codon or after the STOP codon?
They do not get translated.
Is life inevitable?
1) even with all of these conditions life is improbable and the origin of life is not likely
2) if these conditions are met life is likely to begin
What has the rover opportunity found evidence of on Mars?
found evidence of past running water. Pebbles were found which were likely too large to have been carried by wind and resemble fossil stream beds from Earth.
outlines of what look like channels created by water flow which look very similar to dry river valleys on Earth
Where on mars does water exist?
water exists on the Martian surface at the poles but it is in the form of ice mixed with dust and frozen CO2
there is also evidence of water ice in impact craters
What happens during seasonal changes on Mars?
seasonal changes show channels forming, and widening before ‘drying up’ again.
one possible explanation is the presence of very salty water.
What globules were found on Mars?
presence of 300 micrometere carbonaceous globules – suggested that they could only develop in water
Were what found in the globules?
Within the globules were worm-like structure.
What were detected due to the globules?
Large organic molecules.
Does organic molecules = life?
now known to be alternative ways that the organic molecules could arise without the need for life
What is magnetite used for on earth?
on earth some bacteria use magnetite as a means of determining their aspect in terms of the earth’s magnetic field (i.e. which way is down)
Why is life beyond Mars unpromising?
solar flux is much lower so any energy from the sun at the orbit of Jupiter and Saturn is weak
What may be under the surface of Europa?
possibility of a liquid ocean beneath the surface of Europa
What are the lakes made of on Titan?
there are liquid lakes on titan but not of water
these are lakes of liquid hydrocarbons (ethane, methane)
What does Titan atmosphere made up of?
thick atmosphere consists mostly of nitrogen and methane but also containing complex carbon compounds
suggests that plenty of organic material exists in the outer solar system
How are we able to detect extrasolar planets?
using either changes in Doppler shift of stars or detecting changes in brightness due to transits of planets
refinement of these techniques has led to the discovery of earth-sized planets
Why are the discovered earth sized planets uninhabitable?
the vast majority of earth-sized planets so far discovered have been close to their star
i.e. outside the habitable zone
Where does the search for life bearing planets cocnentrate?
the search for extrasolar planets that are potentially life-bearing concentrates on those that surround their star’s habitable zone
What does the size of the habitable zone depend on?
the size of the star itself.
Where is Proxima Centauri b ?
A planet orbiting the nearest star which lies in the Goldilocks zone.
What does life leave behind?
Chemical signatures. For instance the presence of molecular oxygen in the Earth’s atmosphere is due to photosynthesis (plants, algae, cyanobacteria). Likewise the presence of methane (CH4) is due to its production by Archaeans. Currently this is difficult but with better telescopes and an increased number of known exoplanets this may be possible
What happens when oxygen molecules appear in the atmosphere in significant quanitities?
once oxygen molecules (O2) appear in the atmosphere in significant quantities we get conversion of a proportion of these molecules into ozone (O3)
What does ozone do?
the important thing about the presence of ozone is that it blocks short wave UV radiation which damages DNA
Why is the ozone layer described as dynamic?
the ozone layer is dynamic – ozone is continually being built up and broken down by the action of UV radiation
What suggestions have been made as to why life developed on earth?
1) the presence of Jupiter in the outer solar system
- acts as a gravitational attractant for comets, meteorites and asteroids (e.g. Comet Shoemaker-Levy)
2) the presence of the Moon
- the moon has a stabilising effect on the Earth’s rotation. It is by far the biggest satellite in comparison to it’s mother planet
