Life in the Universe
FACT:
At present, there is no
evidence of life forms
other than on the planet
Earth.
Astronomers…
are split on whether or
not life is probable
elsewhere in the
universe.
The earth is about 4.6BY old.
Fossils of the first life forms appear in rocks
about 3.5 BY
This means there have been simple life forms
here for much of the planets history.
More complex forms appear in rocks about
600 MY ago.
Our species,
Homo Sapiens, has existed for about
500,00years—only one-ten thousandth of the
age of the planet.
The Earth’s life forms
• are made of the same elements as the earth
is made of.
• There is remarkable commonality among the
building blocks (e.g. amino acids, proteins,
DNA) of the earth’s diverse life forms.
The scientific position is that life on
Earth
evolved fairly rapidly from common origins
(complex organic molecules)
Under controlled conditions,
• It is possible to stimulate compounds
thought to be common in the Earth’s early
atmosphere methane, Ammonia) to produce
organic molecules and amino acids.
Organic material so produced
• has been found to spontaneously generate
structures which isolate sections of the
sample (primitive cell wall?)
Complex organic molecules
are also found in interstellar clouds and some
meteorites.
While no experiments have produced
cells which can reproduce
They have produced RNA strands which can
replicate themselves.
It is a common scientific belief
That life originated on earth spontaneously.
Other astronomers hold that life originated
elsewhere and was transported to earth.
PANSPERMIA
The position that life on earth descended from
organisms created elsewhere in the universe.
e.g. as bacteria transported in dust particles.
(Not generally supported today)
EVIDENCE FOR OTHER WORLDS:
The “Drake Equation” (Frank Drake)
• There are 1010 stars like the Sun in the Milky
Way.
• If one in ten has a life-sustaining planet, the
total would decrease to 109
• 1 in 100 provided the conditions for the
spontaneous development of life, the total
would be 107
The Drake Equation, continued
• If one in a thousand potential life-supporting
worlds gave rise to a technical civilization,
there would be 104 or 10,000 technical
civilizations in the Milky Way.
Why don’t they call?
• With the radius of the Milky Way being
50,000LY, and assuming 10,000 technical
civilizations, the average distance between
civilizations would be 1000LY.
Soooo,
• If a society learned to use radio waves at the
same time as the Earth, (late nineteenth
century), their first messages would not get
to us until the year 2900.
Even if there are other technical
civilizations,
We would most likely hear from them if:
• They wanted to communicate
• They had mastered space flight and
communication
The Gaia (guy-uh) Hypothesis
James Lovelock/Lynn Margulis, 1974)
The planet Earth and its life forms are in a
symbiotic relationship (they change/affect
each other)
Life forms…
• Adapt to the environment, AND the
environment changes as a result of the
actions of life forms.
In the classic example:
• Early plants produced oxygen, which created
an ozone layer, which protected the plants
from U-V radiation.
• The life forms (plants) changed the planet.
If the planet gets too cold,
• Plants will die off, so less carbon Dioxide is
scrubbed from the atmosphere.
• Since CO2 is a greenhouse gas, the global
temperature might rise.
If the planet gets too warm…
• More plants would grow, so more carbon
dioxide would be removed from the
atmosphere—less greenhouse effect.
CONCLUSION?
• The “numbers” imply that life COULD exist
elsewhere….
• But there is NO direct evidence of that life as
of 2012.