reading: Chapter 5

Lecture 13. Panspermia

announcement: Exam on Friday - move to Monday?availability for office hours: Thursday

Polymerization Problem

amino acid 1 + amino acid 2 <----> dipeptide (aa1-aa2) + H2O

Is called a problem because:1. reaction produces water.2. reactions must occur in the presence of water3. life requires liquid water4. water drives the chemical equilibrium in the wrong direction!

Any valid hypothesis of the origin of life has to explain ThePolymerization Problem.

Somehow organic molecules came together, began reacting.Key: understanding polymerization.

Called “The Polymerization Problem”

Problem of Chirality

Chiral compounds have multiple stereoisomers.Amino acids occur in D and L forms in the universe.

Any valid hypothesis of the origin of life has to explain The Chirality Problem:- amino acids in proteins “chose” L-amino acids- sugars/carbohydrates “chose” D-sugars

When Did Life Originate?

Don’t know when life originated.Knowing when gives us some clues about the environment.

If we have cellular life at 3.8 Ga:- during late heavy bombardment.- origin of life some time before this (4.1-4.2 Ga)- only took a couple hundred million years- hot conditions

If cellular life arose later:- after late heavy bombardment- may have taken much longer to originate - billion years

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Impact Frustration of Life

Likely several 150-190 km diameter impactorsbetween 4.5 and 3.8 Ga.

If life originated in the deep sea:could have originated 4.2 - 4.0 Ga

If life originated at the surface:could have originated 4.0 - 3.7 Ga

Life could have arisen multiple times, and thengone extinct several times.

Panspermia - The Alternative Hypothesis

began with the Greeks!

500 BCE AnaxagorasStated the principal of Panspermia: the seeds of animal and plantlife are inherent to the cosmos, and they take root whenever conditions are favorable.

1908 Svante ArrheniusPut Panspermia in a scientific theoretical frameworkBook “Worlds in the Making”

“…life-giving seeds are drifting about in space. They encounterthe planets, and fill their surfaces with life as soon as the necessary conditions for the existence of organic beings are established.… We must regard it as possible that there are countless seed-bearingmeteoric stones moving through space.”

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Panspermia Unravels

Panspermia treated with skepticism, almost as anti-science.

It moves the problem of the OOL elsewhere.

In the last decade, research in the field of Panspermia hasbeen revitalized. Now treated as a serious field of study.

Perhaps life originated elsewhere in the solar system.Transported to Earth where it then diverged into the diversity of

organisms we are familiar with today.

Alternatively, life transferred from Earth to anotherbody of the solar system.

Observations Suggesting Panspermia is Possible

1. We find intact Mars rock on Earthe.g., ALH84001

best place to find meteorites: Antarctica!- cold (preserves them)- easily visible- ice is melting, so they are concentrated

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2. Bodies are moving through the solar system

3. Organic compounds- are plentiful in the solar system (comets, asteroids, dust)- can survive billions of years in space- can survive atmospheric entry inside meteorites(outer surface melts, inner part still cold as space)

Observations Suggesting Panspermia is Possible, cont.

The Process of Interplanetary Transfer

1. Origin of life has to occur SOMEWHERE

2. Have to get the organisms off the moon or planetonly real way: impacts

- impactor comes in and hits the parent body- material is ejected out of the impact site = ejecta- ejecta = dust and boulders- whether ejecta makes it into space depends on

i. impact energy ii. gravity of the parent bodyiii. whether parent body has an atmosphereiv. how thick the atmosphere of the parent body

wimpy impacts ---> little ejectahuge impacts ---> lots of ejecta, but lots of melting

The Process of Interplanetary Transfer, cont.

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Gravity of the parent body ---> escape velocityMoon: 2.4 km/secMars: 5.0 km/secEarth: 11.2 km/secVenus: 10.4 km/secejecta must have velocity > espace velocity

Atmosphere:a thick atmosphere slows down objects due to drag

Moon: noneMars: 6 mbarsEarth: 1 bar (200x)Venus: 60 bars (60x)

The Process of Interplanetary Transfer, cont.

The Process of Interplanetary Transfer, cont.

3. The organisms have to survive the trip through space

Space Conditions:- extreme cold- T can vary with distance from Sun, whether in sunlight or in the shade- extreme vacuum - desiccating, water boils away- uv light from the Sun - constant exposure- solar storms- galactic cosmic rays

Transfer Time Varies:- martian meteorites average a few million years- lunar meteorites average a few thousand years- thousands to several millions of years

Ejected Material Not Equally Distributed:- material from the inner solar system rarely reaches Jupiter

} energetically charged particles

Spore Formers

Made by a couple species of bacteria.All evolutionarily related.

Found primarily in soils.Some are human pathogens.

BacillusB. subtilisB. anthracis

ClostridiumC. tetani (tetanus)C. botulinum (botulism)C. perfringens (gas gangrene)

Heliobacillusare also photosynthetic!don’t produce oxygen like cyanobacteria

Starved cells undergo a developmental process.Spores have a large number of protective

coatings and layers.Spores have very low water content.Spores highly resistant to:

- heat- strong acids and bases- radiation- heat- desiccation- nutrient depletion- strong oxidants (hydrogen peroxide)

No metabolic activity until nutrients and water are available.

Spores Are Persistent:- 1947 spores of Clostridium grew well when revived in 1981- 2000 year old spores in archaeological materials- 7000 year old spores from Minnesota lake sediments- 30 Ma (controversial) spores in bee guts preserved in amber

Spores

Spores in Space!

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3 missions sponsored by ESA, on a Russian satellite, ‘94, ‘97, ‘99.

Lid opens once in orbit, exposesmaterial in space 10-15 days, lid closes, re-enters atmospherelands.

Treatment: # of Survivors:

Exposed to Space and Sunlight 1/106 (in sunlight)

Below a quartz window

1/10 (in dark)

1/107 (in sunlight)

Under a layer of clay

1/10 (in dark)

1/103 (in sunlight)

Under a layer of meteorite

1/10 (in dark)

1/103 (in sunlight)

Becoming Radiation Resistant

Deinococcus radiodurans“The world’s toughest bacterium”extremely resistant to:

- uv- ionizing radiation- desiccation

lives in:- cores of nuclear power plants- deserts- Antarctica- soils

Can survive 3,000,000 radsHuman lethal dose: 500 rads

Survives well because it repairs DNA damage rapidly.Prevents damaging free radicals OH• from accumulating in the cell.

The Process of Interplanetary Transfer, cont.

4. Organisms in space have to survive impact onto new body

Several Aspects:- heating- acceleration- size of meteorite

small: burst in atmosphere and burn uplarger: outer surface melts, forms a fusion crustvery large: impactor melts or vaporizes upon impact

- impactor has to break up to release the organisms

5. Organisms have to survive, grow, and reproduce. Haveto find an optimal environment.

Is Panspermia common or rare now?

Has life been transferred once or twice?

Have their been many origins of life on other parent bodies?

reading: Chapter 5

Lecture 14. Source of Organic compounds, Miller-Urey Experiment

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Cassini Spacecraft found older terrainsand major fractures on moon Enceladus

Course crystalline ice which will degrade overtime.

Must be < 1000 years old!Organic compounds found in the fractures.Must be heated - required T > 100K (-173˚C)Erupting jets of water observed.Cause of eruptions not known….

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Mystery of Enceladus

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