What is Exobiology

• Exobiologists study how life may have originated here on Earth and where it may also exist in the universe.

What Is Life?

• 1. The basic units of life are cells.• A. All living organisms are either single-celled

or multicellular.

• B. Cells are bounded by membranes and contain DNA and RNA.

• 1. DNA contains the genetic code.

• 2. RNA translates the genetic code into proteins.

Other Properties of Life

• C. Living organisms reproduce either individually or in pairs.

• D. Living cells carry out complex chemical reactions to convert materials and energy for their own use (metabolism).

Two Types of Cells

• Prokaryotic cells contain no nucleus.• 1. Bacteria are prokaryotic cells.• 2. First organisms to show up in the fossil

record are prokaryotes.

• Eukaryotic cells.• 1. More complicated structure then prokaryotic

cells.• 2. Multicellular organisms have eukaryotic

cells.

Two Types of Cells

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Requirements For Life to Exist

• Significance of water.• 1. Water is essential to the chemistry of all

biological systems.

• 2. It is the medium in which biochemical reactions take place in.

• 3. In looking for signs of life either here on Earth or elsewhere scientists look for signs of liquid water.

Cells Are Made of Molecules

• All cells and their constituents are made of 4 types of biomolecules.• Carbohydrates: sugars and starches.

• Proteins: composed of amino acids.

• Lipids: fats which are composed of long chain fatty acids, glycerol, phosphate groups, etc.

• Nucleic Acids: DNA and RNA, composed of nucleotides. Adenine, Thymine, Guanine and Cytosine

Biomolecules are Organic Compounds

• Biomolecules are large molecules with a carbon skeleton.

• Organic compounds are those molecules that contain carbon.

• All life as we know it is based on carbon compounds.

• Did organic compounds arrive on earth via comets?

Origin of the Molecules of Life

• Miller-Urey Experiment.• 1. Early atmosphere was believed to contain methane,

ammonia, water and hydrogen.• Miller created such an "atmosphere." It consisted of

methane, ammonia, water and hydrogen above an "ocean" of water. Then he subjected the gases to "lightning" in the form of a continuous electrical discharge. After a few days, he analyzed the contents of the mock ocean.

• He found a mixture of organic compounds and amino acids in the artificial ocean.

Miller’s Experiment

Origin of Life on Earth (II)

Chemosynthesis

1st phase: hydrocarbon chains formation from ammonia, water and hydrogen (the Miller - Urey experiment).

These complex molecules were formed in the air and accumulated in the oceans.

Where Did Life Originate on Earth?

• Deep Sea Thermal Vents?• A. First discovered in 1979.

• B. Scientists discovered whole ecosystems of organisms living in the absence of sunlight.

• Panspermia?• A. Life arose from extra-terrestrial sources?

• Frozen Ocean Hypothesis?

Deep Sea Vent

Panspermia

• A theory developed by Svente Arrhenius.

• The theory states that life did not originate on the Earth, but originated elsewhere in the universe.

• Plausible if we find life on other worlds.

Frozen Ocean Hypothesis

• Three billion years ago, the Sun was thirty percent less luminous than it is today.

• The first 300 meters of the ocean was frozen.

• The layer of ice protected organic molecules from ultraviolet radiation.

• These organic molecules were supplied by hydrothermal vents.

The Search For Life Outside Earth

• The Planet Mars.• 1. The Viking missions found no evidence of

organic compounds in the Martian soil.

• 2. ALH84001.• A. A meteorite found in Antarctica and determined

to have originated from Mars.

• B. Along tiny cracks scientists discovered signs of what appears to be fossilized bacteria.

ALH84001

• There are four main clues which bring some scientists to this conclusion.• 1. The meteorite is definitely of Martian origin.

• 2. The presence of complex organic molecules.

• 3. The presence of bacterial metabolites.

• 4. The pictures of the possible fossilized bacteria themselves.

ALH84001

Mars Pathfinder Mission

• This probe landed near the Ares Vallis region of Mars.

• This site may have been hot and wet at one time.

• This area may have been like the Yellowstone area where microbes flourish today.

The Little Rover That Could

“Bacteria-the Space Colonists?”

• I always thought the most significant thing we found on the whole @#$% Moon was that little bacteria who came back and lived and nobody ever said &#$@ about it. — Pete Conrad, Commander Apollo 12, 1969

• Mr. Conrad had a colorful way of expressing himself through the English language.

“Bacteria-the Space Colonists”

• On April 20, 1967, Surveyor 3 landed on the moon near Oceanus Procellarum.

• Aboard was a television camera.

• On November 20, 1969, Apollo 12 astronauts Pete Conrad and Alan L. Bean recovered the camera. When NASA scientists examined it back on Earth they found specimens of Streptococcus mitis that were alive.

Is There Life Elsewhere in The Solar System?

• NASA is currently looking at three other possibilities; Mars, Europa and Titan.

Jupiter’s moon Europa

• Evidence from images taken by Galileo show regions resembling ice flows on Earth.

• The heat generated by tidal forces due to interactions with Jupiter’s gravity field may be enough to liquefy some portion of Europa’s icy crust.

• Could Europa support microbial life?

Saturn’s moon Titan

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Saturn’s moon Titan

• Laboratory simulations show that a Titan-like atmosphere, primarily a N2/CH4 mixture, under various energetic

excitations will form complex organic molecules and adenine, a component of DNA.

30 Million Year Old Germs

• In 1995, Biologists Raul Cano and Monica Borucki had extracted bacterial spores from bees preserved in amber in Costa Rica.

• When placed in a suitable culture, the spores came right back to life.

• The biologists also attempted to culture from the same amber a number of samples that contained no bee parts. These cultures were negative.

30 Million Year Old Bacteria

Conclusion

• Bacteria can resist adverse conditions by forming spores.

• Bacteria can live under an enormous wide range of conditions most of which would kill eukaryotic organisms.

• The main thing that bacteria need to survive is liquid water.

• If there is other life in our solar system it is most likely bacterial?