Life in the Cosmos Flashcards
All chemical elements except from hydrogen, helium and lithium were formed by what?
Nucleosynthesis in the cores of previous generations of stars and ejected into supernova
Where does star and planet formation take place?
Molecular clouds
3 steps of protoplanet formation
- Condensation into dust molecules
- Accretion into planetesimals
- Coalescence into protoplanets.
First Earth Area
Hadean Era
What was earth like during the Hadean Era
Hot, volcanic and under constant bombardment by meteorites/ planetesimals
Atmosphere in the Hadean Era
Mainly N2, CO2, H2O, CH4, H2
What era were the first ambiguous signs of life?
Archean Era
What is life on earth based on?
Proteins and amino acids
Where have amino acids been detected?
Space, meteorites
What experiment have amino acids been formed in
Miller-Urey
What is outgassing?
Heating and melting of the earths surface drove volatile gases into the atmosphere.
What was the Hadean atmosphere rich in?
CO2
What did the Hadean CO2 rich atmosphere cause?
Greenhouse effect
How did CO2 leave earths atmosphere?
Mainly precipitated out,
Some was returned to atmosphere by plate tectonics
How did the fraction of oxygen in Earths atmosphere start to rise?
Oxygen is produced by photosynthesising organisms
Increase in oxygen conc. marks the start of what era?
Proterozoic era
What is the Pre-Cambrian Era made up of?
Archaean Aeon and Proterozoic Aeon
What does the Pre-Cambrian Era constitute?
The vast majority of the time for which life has existed on Earth
Why is oxygen a better element for us to have in our atmosphere?
Its much more reactive than CO2, easier for living organisms to extract energy using aerobic reactions than anaerobic
What is ozone?
A form of oxygen that protects life on earth by screening out the suns UV radiation
What was the Cambrian Explosion?
Huge growth in the number and variety of multi-cellular creaturesW
When was the Cambrian Explosion?
540 Million Years ago
Factors for the growth of diversity?
Oxygen, Genetic complexity, absence of predators
What is the geological year
Representation of the development of life by imagining the lifetime of the Earth compressed into a single year.
What is the K-Pg extinction?
The extinction that killed the dinosaurs
What do scientists think the K-Pg extinction was caused by?
Impact of a 10 km meteorite
Evidence for the K-Pg extinction being caused by a large meteorite?
Large crater of the right age, and a high iridium abundance at the K-Pg boundary, consistent with that found in meteorite material
Fossil record provides evidence for how many mass extinctions?
20
Which events have a much higher probability of occuring than large, energetic events
Small, less energetic events
The bigger an impacting meteorite, the bigger the ______
BANG
Do meteorites always leave a crater?
No not always
If a meteorite doesnt leave a crater, can it still cause damage?
Yes - considerable amounts of damage
What was the Tunguska airburst?
A meterorite or comet exploded in the earths atmosphere, about 8 km above the ground
How does an explosion above the ground happen?
Rapid heating due to friction with molecules in the atmosphere
Effects of the Tunguska airburst
- Shock wave flattened a 2000 km area
- Forest fires that burned for weeks
- Ash and debris sent to atmosphere, carried around the world m
When did the most extreme extinction occur?
Between the Permian and Triassic Eras
What percentage of organisms were lost in the Permian-Triassic extinction?
90% of ocean species
70% of all land vertebrate species
What is life defined as?
A material system which as the ability to self-replicate, mutate and evolve in response to changing environments
What must a system do in terms of energy and raw materials to repair itself?
Must be able to draw energy and process raw materials to repair itself.
What are optimal conditions
Conditions we would look for to maximise our chances of finding extra-terrestrial life
Carbon forms bonds with itself, creating _____ bonds
Covalent
Are carbon-carbon covalent bonds strong?
Yes, take a lot of energy to break therefore can withstand high levels of heat.
Where does carbon place in terms of how abundant it is in the universe?
4th most abundant element in the universe
Why is carbon such a succesful element?
Forms a greater variety of chemical compounds than any other element, Has the greatest ability of any element to bond with itself, can form long chain molecules that encode information
Why is silicon not as likely to be the basis of alien life than carbon?
Bonds arent as strong
Cant form double bonds
Silicon more likely to bond with oxygen into a small molecule than form long chain molecules
What is a deep-sea smoker?
Deep sea geothermal which is expelling extremely hot mineral rich water from within the Earths Crust.
What element were the ecosystems found around deep sea-smokers based on
Sulphur
What word describes bacterial colonies that live around the deep sea smokers and metabolise sulphur compounds?
Anaerobic
When colonies live deep down in the sea with no sunlight, where do they get energy from?
Sulphur chemistry
Where do many scientists believe life orginated?
Deep sea smokers, due to chemical reactions in the mineral-rich waters.
What factors make up the overall environment of a planet?
Temperature, mass, age and atmospheric composition
What are the compounds that if present are hopeful signs of life?
Water, oxygen and carbon
What other conditions are necessary to protect life?
Protection from radiation, Moderate and stable temperatures, atmospheric recycling mechanisms
What is the electromagnetic spectrum?
A continuous spectrum of energy-carrying waves of electric and magnetic fields
The shorter the wavelength, …
The greater the energy
Is short or long wavelength radiation more dangerous?
Short
Why are shorter wavelengths more dangerous?
They have enough energy to break bonds in carbon chemistry
How are we (carbon life) protected from radiation?
Ozone layer
For liquid water to survive on a planetary surface, the planet must lie within the _______
Habitable Zone
What is the habitable zone?
The range in distance from the central star in which water can exist as a solid
What happens if a planet is too close to its central star?
It will recieve a lot of heat radiation, overheating. Water will evaporate.
If planet lies outside of habitable zone?
Planet too cold, water will freeze.
What makes Venus and Mars interesting candidates for the search of extra-terrestrial life?
They are both very near the edge of the habitable.
A star hotter than ours will have a more _____ zone
Distant
A star cooler than ours will have a _____ zone
Closer
