Lecture 6 Flashcards
Why does astrobiology study extremophiles?
To determine what could have survived rather than where life could arise.
What are some criteria considered necessary for a planet to create life?
It has to be the right distance from its host star
It has to provide the right habitat for simple life
It need to have liquid water available
It has to retain its atmosphere and water
It need to have a “thermostat” that can retain the right temperatures as atmosphere and heat influx evolve
It has to have a star with the right mass and metallicity
to have a sufficient long lifetime and planetary building blocks
The star must not put out to much radiation (UV, X-Ray)
The planet may have to have a magnetic field to deflect radiation
It may have to have a Large Moon to stabilize tilt
Distance, Habitat, Water, Atmosphere, Thermostat, Metallicity, Mass, Radiation, Magnetic field, Moon(?)
(WHATDRMMMM)
Why would it be important for the planet to have the right mass?
Large enough to retain atmosphere and ocean
Small enough to not retain to much atmosphere
Enough heat for plate tectonics
Solid/molten core
Not too much ocean and not too little
What and where is the galactic inhabitable zone?
In the center where radiation is higher. Dangerous stars, supernoave, pulsars and magnetars increase in number as we move towards the center. There are also regions that contain only old low-metallicity stars (Often found in the halo, pop II stars).
Where are the galactic habitable zones?
Somewhere where star formation rate and radiation exposure is low. Spiral arms are a good fit for this.
Why must the early universe have been void of life?
All of the necessary elements for life are created inside stars and were probably not present in abundance for the first 2 Gyr.
What defines (simply) the habitable zone of a star?
The region where water is liquid.
What is the Continous habitable zone? (or Circumstellar HZ)
The HZ that has been habitable since the formation of the sun. It is much thinner than the region today but modified by the CO2-silicate cycle thermostat.
What is the reason CO2 is such an efficient thermostat?
Because of its IR properties. It lets through visual light almost completely while blocking most IR wavelength totally by absorbing the energy.
What is the problem with the habitable zones of less massive stars?
The HZ is so close that the planets will have tidally locked rotation and thus a cold, dark side where the atmosphere will freeze out without a very dense e.g. CO2 atmosphere being present
What did the discovery that the Sun was 30% less luminous 4 Gyr ago than today imply?
This implied a denser atmosphere or at least containing some greenhouse gases, The increasing luminosity also implied a mechanism that could work as a thermostat.
What is our planets thermostats? What do they depend on?
The Co2 silicate cycle. And the physical processes are weathering/erosion and volcanism. They depend on the existence of plate tectonics.
How does the CO2-silicate thermostat work?
If the Earth’s temperature goes up 🡺 weathering increases
This removes CO2 from the atmosphere cooling the planet
The silicates are brought down into the mantle of the Earth where the CO2 is released again
In the meantime the lowered temperatures in the surface/atmosphere 🡺 weathering diminishing.
Volcanic ejection of CO2 into the atmosphere , possibly accompanied by increased volcanism periodically 🡺 leads to CO2 build-up
This then increases the Earth’s temperature
Negative feedback system
If temp go up 🡺 Weathering removes CO2 from atmosphere 🡺 Cooling 🡺Silicates down into mantle (silicates formed by erosion, ex CO2 in water)🡺CO2 released from mantle 🡺 Weathering diminishes bc lowered temp 🡺 Volcanic ejection 🡺 CO2 build up 🡺 Temp increases
What is the difference between weathering and erosion?
Weathering is the breaking down of rocks, soils, minerals, wood, living things and even artificial elements.
The mechanism is water or biological agents.
Erosion is the transportation of rocks, minerals by wind, water, ice, snow, waves, gravity.
What would happen if the earth didn’t have tectonic activity?
The sediments travel with the tectonic plates (2.5cm per year). Eventually they disappear down into the mantle.
If the Earth did not have tectonic activity (like Venus) the surface would weather down and and very little land would remain, the thermostat would stop working.
How does a planet get out of a snowball event?
Since volcanism continues the emission of greenhouse gases eventually heats the planet.
How long does the freezing and un-freezing of a snowball earth take?
1K to 100K yrs to freeze, 1Myrs to un-freeze.
How did the organisms in the sea have to adapt to a snowball event?
I. They had to evolve enzymes that could mitigate the ravages of dissolved molecular oxygen and hydroxyl radicals.
II. With the banded iron formations precipitating out from seawater, living cells no longer had iron available in the surroundings. Proteins within cells had to be re-engineered for low iron environments.
Why would the first global glaciation have been biologically important?
I. It brought on the (first?) maybe largest ever mass extinction in the history of life on the Earth, by wiping out essentially all anoxic life: Globally freezing temperatures, isolation of Sunlight from the oceans and the removal of all water from the surface of the continents removed the habitats for essentially all life.
II. After 30 million years the Earth went from cold to hot and from oxygen-free to oxygen rich. Life had to adapt very rapidly and this can still be seen in our DNA
What is the definition of a mass extinction?
At least 75% of the species should go extinct.
What are the 5 (known) mass-extinction events?
END-ORDOVICIAN: The party is over About 443 million years ago END-DEVONIAN: Slow extinction is also extinction 359 million to 380 million years ago END-PERMIAN: The Big One 251 million years ago END-TRIASSIC: Repetition 201 million years ago END-CRETACEOUS: The one we all know 65.5 million years ago
(ODPTC)
What caused the End-ordovician mass extinction?
Two sudden climate shifts. About 86% of of species went extinct.
(First, ice sheets advanced, creating a harsh climate in the equatorial and mid-latitude regions.
Then comes a sudden melt, another climate shift.)
What caused the end-devonian extinction?
It was a slow one. A number of events leading to climate change over 20 million yrs. Amongst them, volcanic activity in Siberia. About 75% of species went extinct. Placoderms, more Trilobites and Corals went extinct.
What caused the end- permian extinction?
Volcanic activity in siberia spewed toxic gas and acidified the oceans. About 96% of species went extinct. Forests burned and created a charcoal gap in layers. One synapsid may have lived through it all which lead to dinosaurs and mammals.
What caused the end-triassic extinction?
Volcanic activity in the mid-atlantic. 80% went extinct. The dinosaurs really take over.
What caused the end-cretaceous extinction?
A large piece of solar system material slams into what would become the mexican Gulf/Yucatan peninsula, together with the Deccan and other general volcanism.
About 76 percent of species went extinct.
