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1
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- Chapter Outline
- Life on Earth
- Life in the Solar System
- Life Around Other Stars
- The Search for Extraterrestrial Life
- Interstellar Travel
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- Life appears to share these properties:
- Order
- Reproduction
- Growth and development
- Energy utilization
- Response to the environment
- Evolutionary adaptation
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3
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4
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- Life on Earth thrives in a wide range of environments, and in general
seems to require only three things:
- a source of nutrients,
- a source of energy,
- and liquid water.
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5
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6
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7
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8
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9
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10
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11
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12
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- 4.5 BY/BP Igneous Formation, possibly from ancient Martian Volcano
- 4.0 BY Shock heated, probably from Asteroid impact.
- 3.8 BY Carbonate globules formed
- 1.2 BY Possible second shock event
- 16 MY Blasted off Mars by 2-3 km Asteroid impact
- 13 KY Arrived in Antarctica
- 1996 McKay et al., Search for Past Life on Mars: Possible Relic
Biogenic Activity in Martain Meteorite ALH84001, Science, 273, 924-930.
- Key pieces of evidence:
- Organics (PAHs)
- Carbonate globules
- Fossil Cells (?)
- Magnetite and Greigite
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13
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- Europa probably has a subsurface ocean of liquid water, and may have
undersea volcanoes on its ocean floor. If so, it has conditions much
like those in which life on Earth probably arose, making it a good
candidate for life beyond Earth.
- Ganymede and Callisto might have oceans as well.
- Titan may have other liquids on its surface, though it is too cold for
liquid water. Perhaps life can survive in these other liquids, or
perhaps Titan has liquid water deep underground.
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14
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15
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16
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- We don’t know, but the Drake equation gives us a way to organize our
thinking about the question.
- The equation (in a modified form) says that the number of civilizations
in the Milky Way Galaxy with whom we could potentially communicate is
- Nciv = NHP x flife x fciv x fnow
- where:
- NHP is the number of habitable planets in the galaxy,
- flife is the fraction of habitable planets that actually have life on
them,
- fciv is the fraction of life-bearing planets upon which a civilization
capable of interstellar communication has at some time arisen, and
- fnow is the fraction of all these civilizations that exist now.
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- Convenient interstellar travel remains well beyond our technological
capabilities, because of the technological requirements for engines, the
enormous energy needed to accelerate spacecraft to speeds near the speed
of light, and the difficulties of shielding the crew from radiation.
- Nevertheless, people have proposed ways around all these difficulties,
and it seems reasonable to think that we will someday achieve
interstellar travel if we survive long enough.
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21
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22
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- It seems that we should be capable of colonizing the galaxy in a few
million years or less, and the galaxy was around for at least 7 billion
years before Earth was even born.
- Thus, it seems that someone should have colonized the galaxy long
ago—yet we have no evidence of other civilizations.
- Every possible category of explanation for this surprising fact has
astonishing implications for our species and our place in the universe.
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24
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25
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- Tens of thousands of past human generations have walked this Earth, but
ours is the first generation with the technology to study the far
reaches of our universe and to travel beyond the Earth.
- One can image our descendants living among the stars, having created or
joined a great galactic civilization.
They will have the privilege of experiencing ideas, worlds, and
discoveries far beyond our wildest imagination.
- It is up to our species to decide whether we will use this technology to
advance our species or to destroy it.
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Notes
