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Life in the universe
Transcript of Life in the universe
Life on Earth
When did life arise on Earth?
How did life arise on Earth?
What are the necessities of life?
Fossil evidence puts the origin of life at least 3.5 billion years ago, and carbon isotope evidence pushes this date to more than 3.845 billion years ago!
Life therefore arose within a few hundred milllion years after Earth's formation, and possibly in a much shorter time.
Genetic evidence suggests that all life on Earth evolved from a common ancestor that was probably similar to microbes living today in hot water near undersea volcanic vents or hot springs.
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
We do not know how this first organism arose, but laboratory experiments suggest that it may have been the result of natural chemical processes on early Earth.
Once life arose it rapidly diversified and evolved through natural selection.
Life in the Solar System
Could there be life on Mars?
Could there be life on Europa or other jovian satellites?
If life arose, it might still survive in pockets of liquid water underground.
Europa probably has a subsurface ocean of liquid water and may have volcanoes on its ocean floor.
If so, it has conditions much life those in which life on Earth probably arose, making it a good candidate for life.
Ganymede and Callisto might have oceans as well.
Titan may have other liquids on its surface, though it is too cold for liquid water.
Life around other stars
Where might we find habitable planets?
Are Earth-like planets rare or common?
Billions of stars have at least moderate size habitable zones in which life-bearing planets might exist.
With the Kepler mission, scientists hope to soon find evidence of potentially habitable worlds
We don't know if Earth-like planets are common. Arguments can be made on both sides of the question.
NASA's Kepler Mission
The search for extraterrestial intelligence
How many civilizations are out there?
How does SETI work?
We don't know, but the Drake equation gives us a way to organize our thinking about thequestion.
Number of civilizations with whom we could potentially communicate:
= (hp) x (f_life) x (f_civ) x (f_now)
hp = total number of habitable planets in galaxy
f_life = fraction of habitable planets with life
f_civ = fraction of life-bearing planets with civilization at some time
f_now = fraction of civilizations around now
SETI, the search for extraterrestrial intelligence, generally refers to efforts to detect signals coming from civilizations on other worlds.
Interstellar travel and its implications to civilization
How difficult is interstellar travel?
Where are the aliens?
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
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.
A civilization capable of interstellar travel ought to be able to colonize the galaxy in a few million years or less, and the galaxy was around for billions of years before Earth was formed.
It seems then that some civilization should have colonized the galaxy long ago!
Spaceship powered by an interstellar ramjet.
Where are they???
Mars once had conditions that may have been conductive to an origin of life.
In the deepest sense the search for extraterrestrial intelligence is a search for ourselves. -Carl Sagan
The Voyager Golden Records are phonograph records which were included aboard both Voyager spacecraft, launched in 1977.
They contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for any intelligent extraterrestrial life form, or for future humans, who may find them.
The Pioneer plaques are a pair of gold-anodized aluminium plaques which were placed on board the Pioneer 10 and 11 spacecraft, featuring a pictorial message, in case either spacecraft are intercepted by extraterrestrial life.
The Arecibo message was broadcast into space a single time at a ceremony to mark the remodeling of the Arecibo radio telescope in1974.
It was aimed at the globular star cluster M13 some 25,000 light years away because M13 was a large and close collection of stars that was available in the sky at the time and place of the ceremony.
View from Europa
We've reached out to the stars...
The energy needed to accelerate a single ship the size of Star Trek's Enterprise to just half the speed of light would be more than 2000 times the total annual energy use of the world today.
We are alone.
Civilizations are common, but no one has colonized the galaxy.
There IS a galactic civilization, but it has not yet revealed its existence to us.
Aliens have been a staple of science fiction books and movies
Very, very, very speculative!!
Anybody down there???