-
When did life begin?
- -
- Stromatolies say 3.5 but more controversial evidence
- using microfossils and isotopes have evidence of at least 3.85 billion years
- ago
-
Stromatolites
- -
- Rocks that are characterized by a distinctive, layered
- structure
- -
- Living stromatolites – contain layers of sediments
- intermixed with different types of microbes
-
Microfossils
- microscopic fossil, hard to find because rocks
- become rare with age, so they tend to get destroyed
-
Isotopic evidence
- -
- isotopic analysis of ancient rocks on earth
- o Living
- organizism can change the ratios of isotopes
-
What did early life look like?
- -
- resembled modern extermophiles living in hot water near
- deep-sea vents or in hot springs
-
Where did life begin?
- -
- Deep-sea vents or hot
- springs
- -
- They would have protected from impact that might
- vaporize surface hot springs
-
How did life begin?
- -
- Organic molecule were found in ocean locations where
- clay and other minerals were common
- -
- Clay helped catalyze the building of RNA strands that
- became enclose in lipid pre-cells.
- -
- Some RNA strands were able to self-replicate allowing
- natural selection
-
Could life have migrated to earth?
- -
- originating from Venus or Mars could survive the
- journey
- -
- highly unlikely from longer migrations
-
What major events have marked involuntary history?
- -
- life diversified rapidly after its origin, but remained
- microscopic for more than 2 billion year.
- -
- Oxygen-producing photosynthesis – released the oxygen
- now in our atmosphere
- -
- Multicellular animals diversified in the Cambrian
- explosion, starting about 545 million year ago
-
Why was the rise of oxygen so important to evolution?
- -
- Aerobic processes = more efficient cellular energy
- production than anaerobic processes
- o Lead
- to much greater evolutionary diversification
- -
- Rise of oxygen began before 2.35 billion years ago
- o Did
- not reach levels like present until after the Cambrian explosion
-
Where do we expect to find building blocks of life?
- o But
- small numbers of worlds contain more complex organic molecules
- -
- The fact that they are present in asteroids and comets
- suggest that we’ll find them many places
-
Where can we expect to find energy for life?
- o Weakens
- with distances from sun & unlikely to be sufficient at large distances
- o Probably
- available in more places, likely on any world with a substantial atmosphere or
- liquid medium that can mix and support chemical reactions
-
Does life need liquid water?
- o A
- wider & higher range of temps in which it is liquid
- o The
- type of chemical bonding made possible by charge separation within water
- molecules
- -
- Cannot rule out other liquids: Liquid ammonia, methane
- or ethane
-
What are the environmental requirements for habitability?
- -
- main requirement when looking for habitable worlds:
- possibility of liquid water
- o Molecules
- from which to build living cells
- o A
- source of energy for metabolism
- o Liquid
- medium for transporting chemicals
-
Does life seem plausible on the moon or Mercury?
- -
- No, since neither has liquid water or any other liquid
- medium for life
-
Could life exist on Venus or Mars?
- -
- Not on Venus, it is too hot for liquid water to exist
- on or under the surface
- -
- Might be in Venus’s atmosphere, where clouds contain
- droplets of water.
- -
- Mars had habitable conations in the past and might
- still have it underground
-
Could there be life in the atmosphere of the Jovian planets?
- -
- Jovian plants = have depths at which liquid water can
- exist in their atmosphere
- -
- Strong vertical winds makes life seem unlikely
-
Could there be life on the jovian moons or other small
bodies of the solar system?
- -
- A few large moons may contain liquid water, so maybe
- -
- Smaller moons don’t have any liquid
- -
- There may have been liquid water in the distant past
-
How did we get the idea there could be life on Mars?
- -
- Superficial similarities between mars and earth led to
- speculation
-
Who was Percival Lowell?
- -
- Thought he saw canal built by an advanced society, but
- the canals do not really exist
-
What is Mars like today?
- -
- Atmospheric pressure so low that water is unstable.
- -
- Weather is driven largely by seasonal changes
-
What are the main geological features?
- -
- Densely cratered and must be very old
- -
- Other regions with fewer craters must be much younger
- -
- Giant volcanoes on certain regions
- -
- Evidence of past tectonics, which probably created
- Valles Marineris
-
What evidence do we have there use to be water on the
surface of mars?
- -
- Orbiting images of eroded craters, dry river channels
- o Supporting
- evidence found in chemical analysis of Martian rocks
- -
- Periods of rain fall ended at least 2-3 billion years
- ago
- -
- Still has water ice underground
-
Why/How was Mars warmer and wetter in the past?
- -
- Atmosphere was once much thicker with a much stronger
- greenhouse affect
- o Don’t
- know if this really made Mars warmer or wetter
-
Why did Mars change?
- -
- Loss of atmospheric gas, which weakened the greenhouse
- affect
- -
- Some blasted away with impact others stripped away from
- solar wind
- Water was lost because ultraviolet light could break
- apart water molecules
-
Is Mars Habitable today?
- -
- May have habitable regions today
-
Is there evidence of life on Mars?
- -
- Viking experiments produced results some scientist
- think may be evidence of life, but non biological explanations seem more likely
-
Is there evidence for life in Martian meteorites?
- -
- 4 types of evidence from ALH84001
- o The
- carbonate grains have a layered structure; which on earth this type of layering
- generally occurs only as a result of biological activity
- o Carbonate
- grains contained PAHs
- o They
- saw crystals of the mineral magnetite within the iron-rich layers of the
- carbonate grains; resemble the ones produced by earth bacteria
- o Saw
- rod-shaped structures that look much like recently discovered “nanobacteria” on
- earth
- -
- But each also has a potential non biological
- explanation, so they don’t have a definitive answer
-
General characteristics of Jovian Moons
- -
- Tend to have ice mixed in with their rocks
- -
- Nearly all are in Synchronous rotations
- o Keeping
- 1 side continually turned toward their host planet
-
What makes some of the Galiean Moons warm enough inside to
possibly harbor life?
- -
- Some moons retain internal heat as a result of tidal heating, along with radioactivity
- -
- A few moons have liquid water, minimum requirements for
- life
-
Does Europa have an ocean?
- -
- Surface show numerous features, including relative lack
- of impact craters, suggesting that liquid or slush from below has gathered up
- -
- It has a magnetic field that assumes it has a salty
- ocean
-
Could Europa have life?
- -
- it has liquid water and elements necessary for life, an
- energy source for life is very limited compared to earth
-
Could other moons of Jupiter have life?
- -
- Ganymed (largest moon in SS) is much like Europa, like
- an icy crust
- o A
- change in its magnetic field suggest it has salty oceans under ground
- -
- Callisto (Farthest out of the Galilean moons, no tidal
- heating
- o Magnetic
- measurements suggest a possible hidden ocean
- -
- Could conceivably offer conditions but low energy
- source
-
Characteristics of Titan
- -
- Has an atmosphere even thicker than earth
- o But
- largely composed of nitrogen, argon, ethane and methane
-
Could Titan have life?
- -
- Huygens probe showed that fluid hydrocarbons on the
- landscape
- o Bitter
- cold temps would greatly slow chemical reactions
- o This
- would make metabolism difficult decreasing the chances for life
- -
- It is possible that pockets of liquid water and
- subsurface oceans of cold ammonia/water mixture
Some energy source fore life might be available
|
|
