Neil F. Comins • William J. Kaufmann III
Discovering the Universe
Eighth Edition
CHAPTER 19
Astrobiology
WHAT DO YOU THINK?
1.
2.
3.
4.
5.
Why is water so important to the formation of
life?
What element is uniquely suited to be the
foundation of life as we know it, and why?
How do astronomers search for extraterrestrial
intelligence?
Have astronomers located any extraterrestrial
civilizations?
If advanced alien civilizations exist, is there any
way they might know of our existence?
In this chapter you will discover…
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what qualities scientists believe are necessary for life to
exist
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why many scientists are open to the possibility that
primitive life exists elsewhere in the solar system

how scientists estimate the number of planets orbiting
other stars that could support complex life

how scientists search for life beyond our own solar
system—and the results of those searches

how we are trying to communicate with extraterrestrial
life
Linear chains of molecules => non-complex, at most
“loops” (not living)
Non-linear chains of carbon => complex, organic
molecules (sugar!)
Non-linear chains of silicon & oxygen
=> inert gels or liquids OR
=> inert rigid rocks
Carbonaceous Chondrite meteorites have organic
molecules!
Thought Question
You have a time machine with a dial that you can
spin to send you randomly to any time in Earth’s
history. If you spin the dial, travel through time, and
walk out, what is most likely to happen to you?
• You’ll be eaten by dinosaurs.
• You’ll suffocate because you’ll be unable to
breathe the air.
• You’ll be consumed by toxic bacteria.
• Nothing: you’ll probably be just fine.
Thought Question
You have a time machine with a dial that you can
spin to send you randomly to any time in Earth’s
history. If you spin the dial, travel through time, and
walk out, what is most likely to happen to you?
• You’ll be eaten by dinosaurs.
• You’ll suffocate because you’ll be unable to
breathe the air.
• You’ll be consumed by toxic bacteria.
• Nothing: you’ll probably be just fine.
Miller-Urey Experiment
Assume “primitive atmosphere”
-Water, CO2, Hydrogen, Nitrogen
Add energy
-Electricity (“Lightening”)
-Heat (“Volcanoes”)
See what happens…
Miller-Urey Experiment
SLIME! 
Laboratory Experiments

Miller–Urey experiment
(& more recent
experiments) show:
Building blocks of life
could form easily &
spontaneously under
conditions of early Earth.
Chemicals to Life?
What are the necessities for life?
What IS life?

Chemically interacts with environment
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Takes in “food”
Expels “waste”
Transforms “food” into energy for metabolic
processes
Reproduces
Necessities for Life
Nutrient source
 Energy (sunlight, chemical reactions,
internal heat)
 Liquid water (or possibly some other liquid
as a “solvent” to allow for chemistry)

Hardest to find
on other planets
Origin of Oxygen

Cyanobacteria
paved the way for
more complicated
life forms by
releasing oxygen
into the
atmosphere via
photosynthesis.
The Chances for
(Intelligent) Life?
Is
there intelligent life elsewhere?
How could we contact them?
How will humanity evolve?
How do we search for life?
Where can we “look” so far?
The Habitable Zone

Distance around our Sun supporting Life

Originally narrow, between Venus & Mars

Depends on planet size, capability of life to
survive in various conditions

Now – Venus to Jupiter? Even Moons of
giant planets?
Habitable Zone
Habitable Zone
Drake’s Equation
N = R* x fplanet x ne x flife x f intell x fciv x L

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N = # intelligent, transmitting civilizations
R* = # stars formed/year
fplanet = fraction of stars w/ planets
ne = # of planets/system that can support life
flife = fraction that develop life
f intell = fraction with life that becomes intelligence
fciv = fraction that produce interstellar communications capability
L = “Lifetime” of how long they try to communicate
Drake’s Equation Example
N = R* x fplanet x ne x flife x f intell x fciv x L
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R* = 40 (400 Billion stars in our galaxy about 10 BY old)
fplanet = 50%
ne = 0.5
flife = 1 (optimistic – we did, so others could too!)
f intell = 1
fciv = 1
L = 10,000 years
N =100,000 communicating, intelligent civilizations in the Milky Way alone!
Drake’s Equation Example
N = R* x fplanet x ne x flife x f intell x fciv x L
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R* = 40 (400 Billion stars in our galaxy about 10 BY old)
fplanet = 50%
ne = 0.1
flife = 0.000001 (one in a million!)
f intell = 1
fciv = 1
L = 100 years (before we blow ourselves up??)
N =<<1 communicating, intelligent civilization in the Milky Way – US!!
The Potential for Human Evolution

50 years…
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Smart prosthetics for limbs AND organs
Genetic ID/elimination of hereditary disease
Computers & AI improve
Nanotechnology increases
Questions…
 Fusion?
 Food?
 Water?
The Potential for Human Evolution

500 years…
Brains/Bodies enhanced (“bionics”)
 Lifetimes, Adaptability increase

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Questions…
 Room to survive?
 Resolve to allow “Cyborgs”?
 Reasons to explore?
The Potential for Human Evolution

5000 years…
What is “human”?
 Fully “artificial” 1000+ year lifetime
 Able to travel for 1000 years@ high speeds
 Able to reach nearby stars…
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Questions…
 What will “we” find?