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
•
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
•
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?