Life in the Universe
Life in the Universe
Seven major phases in the history of the universe:
• particulate
• galactic
• stellar
• planetary
• chemical
• biological
• cultural evolution.
A definition of life
Generally speaking, scientists regard the following as
characteristics of living organisms:
• they can react to their environment and can often
heal themselves when damaged
• they can grow by taking in nourishment from their
surroundings and processing it into energy
• they can reproduce, passing along some of their
own characteristics to their offspring
• they have the capacity for genetic change and can
therefore evolve from generation to generation so
as to adapt to a changing environment.
Extraterrestrial Life
There are two opposing schools of thought:
• Those who feel that life is a naturally occurring
phenomenon and therefore is common throughout
the Universe
• Those who feel that life on Earth is the product
of a series of extremely fortunate accidents and
therefore is very rare and we may be the only
example.
Chemical Evolution
• Early Earth was barren, with shallow, lifeless seas washing
upon grassless, treeless continents
• Outgassing from our planet's interior through volcanoes,
fissures, and geysers produced an atmosphere rich in
hydrogen, nitrogen, and carbon compounds and poor in free
oxygen.
• As Earth cooled, ammonia, methane, carbon dioxide, and
water formed. The stage was set for the appearance of life.
• Natural radioactivity, lightning, volcanism, solar ultraviolet
radiation, and meteoritic impacts all provided large amounts
of energy that eventually shaped the ammonia, methane,
carbon dioxide, and water into more complex molecules
known as amino acids and nucleotide bases
Chemical Evolution
• The idea that complex molecules could have evolved naturally
from simpler ingredients found on the primitive Earth has
been around since the 1920s. The first experimental
verification was provided in 1953 when scientists Harold
Urey and Stanley Miller took a mixture of the materials
thought to be present on Earth long ago—a "primordial soup"
of water, methane, carbon dioxide, and ammonia—and
energized it by passing an electrical discharge ("lightning")
through the gas. After a few days they analyzed their
mixture and found that it contained many of the same amino
acids found today in all living things on Earth.
• About a decade later, scientists succeeded in constructing
nucleotide bases in a similar manner.
Another Choice
•
Some scientists have argued that Earth's primitive atmosphere
might not in fact have been a particularly suitable environment for
the production of complex molecules. Instead, they say, there may
not have been sufficient energy available to power the chemical
reactions, and the early atmosphere may not have contained enough
raw material for the reactions to have become important in any
case. These researchers suggest that much, if not all, of the
organic material that combined to form the first living cells was
produced in interstellar space and subsequently arrived on Earth in
the form of interplanetary dust and meteors that did not burn up
during their descent through the atmosphere.
•
Interstellar molecular clouds are known to contain very complex
molecules, and large amounts of organic material were detected on
comet Halley by space probes when Halley last visited the inner
solar system. Similarly complex molecules were observed on comet
Hale—Bopp.
Biological Evolution
• The fossil record chronicles how life on
Earth became widespread and
diversified over the course of time.
• The study of fossil remains shows the
initial appearance about 3.5 billion years
ago of simple one-celled organisms such
as blue-green algae.
–
Warm, shallow waters favour the growth of microorganisms, particularly cyanobacteria, the simplest singlecelled life form known.
–
Microbial mats built from cyanobacteria and other
microscopic organisms are the building blocks for
stromatolites, the rock-like structures whose origin puzzled
geologists for centuries.
–
Stromatolites – literally layered rocks – are the oldest
form of life on earth dating 3.5 billion years.
–
Stromatolites result from the interaction between
microbes, other biological influences and the physical and
chemical environment.
Shark Bay, AU
•These were followed about 2 billion years ago by more complex one-celled
creatures, like the amoeba.
Multi-cellular organisms such as sponges did not appear until about 1 billion years
ago, after which there flourished a wide variety of increasingly complex
organisms—insects, reptiles, mammals, and humans.
Biological Evolution
To put all this into historical perspective, let's imagine the entire lifetime of Earth to
be 46 years rather than 4.6 billion years.
•Life originated at least 35 years ago, when Earth was about 10 years old.
•Not until about 6 years ago did abundant life flourish throughout Earth's oceans.
•Life came ashore about 4 years ago
•Plants and animals mastered the land only about 2 years ago.
•Dinosaurs reached their peak about 1 year ago, only to die suddenly about 4 months later.
•Humanlike apes changed into apelike humans only last week
•The latest ice ages occurred only a few days ago.
•Homo sapiens did not emerge until about 4 hours ago.
•Agriculture was invented within the last hour,
•The Renaissance—along with all of modern science—is just 3 minutes old!
1 Year Cosmic Calendar
(From The Dragons of Eden - Carl Sagan)
Pre-December Dates
Big Bang
January 1
Origin of Milky Way Galaxy
May 1
Origin of the solar system
September 9
Formation of the Earth
September 14
Origin of life on Earth
~ September 25
Formation of the oldest rocks known on Earth
October 2
Date of oldest fossils (bacteria and blue-green algae)
October 9
Invention of sex (by microorganisms)
~ November 1
Oldest fossil photosynthetic plants
November 12
Eukaryotes (first cells with nuclei) flourish
November 15
December
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
1 Significant
oxygen
atmosphere
begins to develop
on Earth.
2
3
4
5 Extensive
vulcanism and
channel formation
on Mars.
6
7
8
9
10
11
12
13
14
15
16 First Worms.
17 Precambrian
18 First oceanic
19 Ordovician
ends. Paleozoic
plankton.
Period. First fish,
Era and Cambrian Trilobites flourish. first vertebrates.
Period begin.
Invertebrates
flourish.
21 Devonian
Period begins.
First insects.
Animals begin
colonization of
land.
22 First
amphibians. First
winged insects.
23 Carboniferous 24 Permian Period 25 Paleozoic Era
Period. First trees. begins. First
ends. Mesozoic
First reptiles.
dinosaurs.
Era Begins.
28 Cretaceous
Period. First
flowers. Dinosaurs
become extinct.
29 Mesozoic Era
ends. Cenozoic
Era and Tertiary
Period begin. First
cetaceans. First
primates.
30 First evolution
of frontal lobes in
the brains of
primates. First
hominids. Giant
mammals flourish.
31 End of Pliocene
Period.
Quaternary
(Pleistocene and
Holocene) Period.
First humans.
26 Triassic Period.
First mammals.
20 Silurian Period.
First vascular
plants. Plants begin
colonization of land.
27 Jurassic Period.
First birds.
December 31
Origin of Proconsul and Ramapithecus, probable ancestors of apes and men
First humans
Widespread use of stone tools
Domestication of fire by Peking man
Beginning of most recent glacial period
Seafarers settle Australia
Extensive cave painting in Europe
Invention of agriculture
Neolithic civilization; first cities
First dynasties in Sumer, Ebla and Egypt; development of astronomy
Invention of the alphabet; Akkadian Empire
Hammurabic legal codes in Babylon; Middle Kingdom in Egypt
Bronze metallurgy; Mycenaean culture; Trojan War; Olmec culture; invention of the
compass
Iron metallurgy; First Assyrian Empire; Kingdom of Israel; founding of Carthage by
Phoenicia
Asokan India; Ch'in Dynasty China; Periclean Athens; birth of Buddha
Euclidean geometry; Archimedean physics; Ptolemaic astronomy; Roman Empire; birth
of Christ
Zero and decimals invented in Indian arithmetic; Rome falls; Birth of Islam and the
Islamic Civilization
Mayan civilization; Sung Dynasty China; Byzantine empire; Mongol invasion; Crusades
Renaissance in Europe; voyages of discovery from Europe and from Ming Dynasty
China; emergence of the experimental method in science
Widespread development of science and technology; emergence of global culture;
acquisition of the means of self-destruction of the human species; first steps in
spacecraft planetary exploration and the search of extraterrestrial intelligence
~ 1:30 p.m.
~ 10:30 p.m.
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Now: The first
second of New Year's
Day
Life (as we know it)
• Carbon-based life that originated in a liquid water
environment
• It appears that no environment in the solar system besides
Earth is particularly well suited for sustaining life.
• Alternative biologies
– Silicon has chemical properties somewhat similar to those of
carbon and have suggested it as a possible alternative to carbon
as the basis for living organisms.
– Ammonia is sometimes put forward as a possible liquid medium
in which life might develop.
Intelligent Life in the Galaxy
An early approach to this statistical problem is usually known as the Drake equation, after
the U.S. astronomer who pioneered this analysis:
number of technological, intelligent civilizations now present in the Milky Way Galaxy
=
rate of star formation, averaged over the lifetime of the Galaxy
x
fraction of those stars having planetary systems
x
average number of planets within those planetary systems that are suitable for life
x
fraction of those habitable planets on which life actually arises
x
fraction of those life-bearing planets on which intelligence evolves
x
fraction of those intelligent-life planets that develop technological society
x
average lifetime of a technologically competent civilization.
The Drake Equation
• Let's examine the terms in the
equation one by one and make some
educated guesses about their values.
• Bear in mind, though, that if you ask
two scientists for their best
estimates of any given term, you will
likely get two very different answers!
RATE OF STAR FORMATION
• Estimate the average number of
stars forming each year in the Galaxy
simply by noting that at least 100
billion stars now shine in the Milky
Way.
• Dividing this number by the 10-billionyear lifetime of the Galaxy, we obtain
a formation rate of 10 stars per year.
FRACTION OF STARS HAVING PLANETARY SYSTEMS
• If the Condensation Theory is correct, planet
formation is a natural result of the star-formation
process
• Accepting the condensation theory and its
consequences, and without being either too
conservative or naively optimistic, we assign a
value near 1 to this term—
• that is, we believe that essentially all stars have
planetary systems
NUMBER OF HABITABLE PLANETS PER PLANETARY SYSTEM
•
Temperature, more than any other single quantity, determines the
feasibility of life on a given planet.
– The surface temperature of a planet depends on two things: the
planet's distance from its parent star and the thickness of its
atmosphere.
– The extent of the habitable zone is much larger around a hot star than
around a cool one.
• For a star like the Sun (a G-type star), the zone extends from about 0.85
A.U. to 2.0 A.U.
• For an F-type star, the range is 1.2 to 2.8 A.U.
• For a faint M-type star only planets orbiting between about 0.02 and 0.06
A.U. would be habitable.
NUMBER OF HABITABLE PLANETS PER PLANETARY SYSTEM
•
To estimate the number of habitable planets per planetary system,
we first take inventory of how many stars of each type shine in our
Galaxy and calculate the sizes of their habitable zones. Then we
eliminate binary-star systems because a planet's orbit within the
habitable zone of a binary would likely be unstable.
•
Single F-, G-, and K-type stars are the best candidates.
•
Taking all these factors into account, we assign a value of 1/10 to
this term in our equation.
FRACTION OF HABITABLE PLANETS ON WHICH LIFE ARISES
•
Of the billions upon billions of basic organic groupings that could possibly
occur on Earth from the random combination of all sorts of simple atoms
and molecules, only about 1500 actually do occur.
•
Furthermore, these 1500 organic groups of terrestrial biology are made
from only about 50 simple "building blocks" (including the amino acids and
nucleotide bases mentioned earlier).
•
This suggests that molecules critical to life may not be assembled by pure
chance.
•
If a relatively small number of chemical "evolutionary tracks" are likely to
exist, then the formation of complex molecules—and hence, we assume,
life—becomes much more likely, given sufficient time.
•
We will take the optimistic view and adopt a value of 1.
FRACTION OF LIFE-BEARING PLANETS ON WHICH
INTELLIGENCE ARISES
• One school of thought maintains that, given enough time,
intelligence is inevitable.
• In this view, assuming that natural selection is a universal
phenomenon, at least one organism on a planet will always
rise to the level of "intelligent life."
• If this is correct, then the fifth term in the Drake equation
equals or nearly equals 1.
FRACTION OF PLANETS ON WHICH INTELLIGENT LIFE
DEVELOPS AND USES TECHNOLOGY
We need to estimate the probability that intelligent life eventually
develops technological competence. Should the rise of technology
be inevitable, this term is close to 1, given long enough periods of
time. If it is not inevitable—if intelligent life can somehow "avoid"
developing technology—then this term could be much less than 1.
The fact that only one technological society exists on Earth does not
imply that the sixth term in our Drake equation must be very much
less than 1. On the contrary, it is precisely because some species
will probably always fill the niche of technological intelligence that
we will take this term to be close to 1.
AVERAGE LIFETIME OF A TECHNOLOGICAL CIVILIZATION
The last term on the right-hand side of the equation, the longevity of
technological civilizations, is totally unknown.
There is only one known example of such a civilization—humans on
planet Earth.
Our own civilization has presently survived in its "technological" state
for only about 100 years, and how long we will be around before a
natural or human-made catastrophe ends it all is impossible to tell.
•
Combining our estimates for the other six terms (and noting that
10 x 1 x 1/10 x 1 x 1 x 1 = 1), we can say:
The number of technological, intelligent civilizations now present in the
Milky Way Galaxy
= The average lifetime of a technologically competent civilization, in
years.
The Final Estimate
Thus, if civilizations typically survive
for 1000 years, there should be 1000
of them currently in existence
scattered throughout the Galaxy.
If they live for a million years, on
average, we would expect there to be
a million advanced civilizations in the
Milky Way.
According to the 'experts'
•
•
•
John Baugher in his book, "On Civilized Stars", estimates 200 million
advanced civilizations in our galaxy, assuming they all reached this point at
the same time.
Carl Sagan derives an estimate between 50 thousand and one million
advanced civilizations currently existence in the Milky Way today.
An even more important value is the estimated rate that advanced
civilizations occur in the galaxy:
Event
Years Before Now
Adv. Civilizations Occurring
Life on Earth
3.8 billion
38 million
Life on Land
400 million
4 million
Rise of Dinosaurs
200 million
2 million
Rise of Mammals
60 million
600 thousand
Rise of Man
5 million
50 thousand
Rise of Homo Sapiens 300 thousand
3 thousand
Where Are They?
In the 1940's, around a lunch table, some physicists were
discussing extraterrestrial life. Nobel Prize winner,
Enrico Fermi is supposed to have then asked,
"So? Where is everybody?"
What Fermi was asking is if there are all these billions of
planets in the universe that are capable of supporting
life, and millions of intelligent species out there, then
how come none has visited earth?
This has come to be known as The Fermi Paradox.
Where Are They?
• Fermi realized that any civilization with a rocket technology could
rapidly colonize the entire Galaxy.
• Within a few million years, every star system could be colonized.
• A few million years may sound long, but in fact it's quite short
compared with the age of the Galaxy, which is roughly ten thousand
million years.
• Russian astrophysicist Nikolai Kardashev proposed a useful scheme
to classify advanced civilizations:
–
A Type I civilization is similar to our own, one that uses the energy
resources of a planet.
– A Type II civilization would use the energy resources of a star, such
as a "Dyson Sphere".
– A Type III civilization would employ the energy resources of an entire
galaxy.
• A Type III civilization would be easy to detect, even at vast distances.
Bracewell-Von Neumann Probes
• It should be possible for an advanced civilization to construct selfreproducing, autonomous robots to colonize the Galaxy.
• The idea of self-reproducing automaton was proposed by
mathematician John von Neumann in the 1950's.
• The idea is that a device could:
– perform tasks in the real world
– make copies of itself (like bacteria).
• A Bracewell-von Neumann probe is simply a self-reproducing
automaton with an intelligent program and plans to build more of
itself.
• Growth of the number of probes would occur exponentially and the
Galaxy could be explored in 4 million years.
• While this time span seems long compared to the age of human
civilization, remember the Galaxy is over 10 billion years old and
any past extraterrestrial civilization could have explored the
Galaxy 250 times over.
How long would it take?
Propulsion
Maximum Velocity
Worst Case Transit
Fission
0.6 c
2.66 million years
Fusion
0.15 c
1 million year
Laser
0.98 c
160 thousand years
Antimatter
0.999 c
160 thousand years
Ramjet
arbitrarily close to c
160 thousand years
Colonization takes into account the rate at which stops are
required and the amount of time each stop
Propulsion
Time Required to Colonize the Galaxy
Fission
3.8 million years
Fusion
2.14 million years
Laser
1.3 million years
Antimatter
1.3 million years
Ramjet
1.3 million years
Possible solutions to The Fermi Paradox
• They Are Here
– They Were Here and They Left Evidence
• UFO's, Ancient Astronauts, Alien Artifacts
– They Are Us
• Humans are the descendents of ancient alien civilizations. Problem: where
are the original aliens?
– Interdict Scenario
• The aliens are here, and they are keeping isolated or there is an
interdiction treaty to prevent contact
• They Exist But Have Not Yet Communicated
–
–
–
–
They Have Not Had Time To Reach Us
They Are Signaling, But We Do Not Know How To Listen
They Have No Desire To Communicate
Catastrophes
• They Do Not Exist
MEETING OUR NEIGHBORS
•
Our civilization has already launched some interstellar probes, although they have no
specific stellar destination.
•
A plaque was mounted onboard the Pioneer 10 spacecraft launched in the mid-1970s
and now well beyond the orbit of Pluto, on its way out of the solar system.
•
Similar information was also included aboard the Voyager probes launched in 1978.
•
Although these spacecraft would be incapable of reporting back to Earth the news
that they had encountered an alien culture, scientists hope that the civilization on the
other end would be able to unravel most of its contents using the universal language of
mathematics.
The important features of the plaque include
a scale drawing of the spacecraft, a man, and
a woman; a diagram of the hydrogen atom
undergoing a change in energy (top left); a
starburst pattern representing various
pulsars and the frequencies of their radio
waves that can be used to estimate when the
craft was launched (middle left); and a
depiction of the solar system, showing that
the spacecraft departed the third planet
from the Sun and passed the fifth planet on
its way into outer space (bottom). All the
drawings have computer- (binary) coded
markings from which actual sizes, distances,
and times can be derived.
MEETING OUR NEIGHBORS
Pioneer 10 will continue to coast silently as a
ghost ship into interstellar space, heading
generally for the red star Aldebaran, which
forms the eye of the constellation Taurus
(The Bull). Aldebaran is about 68 light- years
away. It will take Pioneer 10 more than two
million years to reach it.
RADIO COMMUNICATION
• SETI
– http://setiathome.ssl.berkeley.edu/
–
There are other projects like this: http://boinc.berkeley.edu/projects.php
Name
parsecs
Age
(Gyr)
Spectral
Type
Notes
Beta Cvn
8.37
4.05
G0 V
Solar Analog
HD10307
12.64
5.91
G2 V
Solar Analog
astrometric binary
HD211415
13.61
3.3
G3 V
CCDM 3”
18 Sco
14.03
4.8
G5 V
CCDM: 26”
Solar Twin
51 Peg
15.36
6.34
G2.5 V
Solar Analog
Giant Planet
CCDM – Catalog of Components of Double and Multiple Systems
This table of possible Habitable Stars was put together by Margaret
Turnbull (U. of Arizona) and Jill Tarter (SETI)
“Target Selection for SETI. II Tycho-2 dwarfs, old open clusters and the nearest 100 stars”, Astrophysical Journal Supplement Series,
129, 423-426, 2003 December.
Exobiology or Xenobiology
• How would the environment shape the
being?
– Physical Structure
– Optical
– Other Senses