Life in the Universe

Life in the UniverseSeven major phases in the history of the

universe: • particulate• galactic• stellar• planetary• chemical• biological• cultural evolution.

A definition of lifeGenerally 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 micro-organisms, particularly cyanobacteria, the simplest single-celled 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. 

• 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.

Shark Bay, AU

Biological EvolutionTo 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 DatesBig 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

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 ends. Paleozoic Era and Cambrian Period begin. Invertebrates flourish.

18 First oceanic plankton. Trilobites flourish.

19 Ordovician Period. First fish, first vertebrates.

20 Silurian Period. First vascular plants. Plants begin colonization of land.

21 Devonian Period begins. First insects. Animals begin colonization of land.  

22 First amphibians. First winged insects.

23 Carboniferous Period. First trees. First reptiles.

24 Permian Period begins. First dinosaurs.

25 Paleozoic Era ends. Mesozoic Era Begins.

26 Triassic Period. First mammals.

27 Jurassic Period. First birds.

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.

December

Origin of Proconsul and Ramapithecus, probable ancestors of apes and men ~ 1:30 p.m.First humans ~ 10:30 p.m.Widespread use of stone tools 11:00 p.m.Domestication of fire by Peking man 11:46 p.m.Beginning of most recent glacial period 11:56 p.m.Seafarers settle Australia 11:58 p.m.Extensive cave painting in Europe 11:59 p.m.Invention of agriculture 11:59:20 p.m.

Neolithic civilization; first cities 11:59:35 p.m.

First dynasties in Sumer, Ebla and Egypt; development of astronomy 11:59:50 p.m.Invention of the alphabet; Akkadian Empire 11:59:51 p.m.Hammurabic legal codes in Babylon; Middle Kingdom in Egypt 11:59:52 p.m.Bronze metallurgy; Mycenaean culture; Trojan War; Olmec culture; invention of the compass

11:59:53 p.m.

Iron metallurgy; First Assyrian Empire; Kingdom of Israel; founding of Carthage by Phoenicia

11:59:54 p.m.

Asokan India; Ch'in Dynasty China; Periclean Athens; birth of Buddha 11:59:55 p.m.Euclidean geometry; Archimedean physics; Ptolemaic astronomy; Roman Empire; birth of Christ

11:59:56 p.m.

Zero and decimals invented in Indian arithmetic; Rome falls; Birth of Islam and the Islamic Civilization

11:59:57 p.m.

Mayan civilization; Sung Dynasty China; Byzantine empire; Mongol invasion; Crusades 11:59:58 p.m.Renaissance in Europe; voyages of discovery from Europe and from Ming Dynasty China; emergence of the experimental method in science

11:59:59 p.m.

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

Now: The first second of New Year's Day

December 31

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 GalaxyAn 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-billion-year 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.

• 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.

Where Are They?

Bracewell-Von Neumann Probes

• It should be possible for an advanced civilization to construct self-reproducing, 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?

Colonization takes into account the rate at which stops are required and the amount of time each stop

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

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

– www.setiathome.org

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