Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization

First Edition

© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm


6.1  Chronology

In 1648 James Ussher, the Archbishop of Armagh, announced that the creation of Earth occurred promptly at 10 A.M., October 23, 4004 B.C. This span of roughly six thousand years was calculated in accordance with the descriptions and geneologies found in the Bible, and enjoyed wide currency until about two centuries ago.

Today we know that the material universe is far older. The primieval fireball is believed to have exploded perhaps sixteen billion years ago, the Milky Way coalescing a few eons later. Such vastness is scarcely conceivable in any meaningful terms.

How does one conveniently comprehend a span of time equal to millions of human lifetimes? Imagine that we draw a line from top to bottom of this page, a linear scale to portray the entire history of the universe. On this map, the sum total of human civilization would be represented by an invisible sliver a few hundred atoms long. On the same scale, the time man has known electricity is measured by the span of two or three atoms. Even the segment illustrating the entire Age of Mammals would hardly exceed a millimeter in length (Figure 6.1).


Figure 6.1 Timescale of Cosmic Evolution (from Barney Oliver, in Duckworth2296)

In 15 billion years the universe has evolved from the blazing inferno of the primordial fireball into galaxies of stars surrounded by planets, many of which may support intelligent life. The earth has existed for approximately one-third this time or 4.5 billion years, while man has been around for only 1.5 million years or one ten thousandths the estimated age of the universe.


One rather well-known visualization was set forth by the famous British astronomer Sir James Jeans many decades ago. Imagine a penny carefully balanced atop the Washington Monument. Affixed to the cent is a postage stamp. Proportionately, the Monument represents the age of the Earth, the coin the entire age of the species of man, and the stamp the length of time since humans first learned to use tools.2109

Our minds are easily boggled. The whole history of the United States spans a mere two hundred years, a series of only eight generations of humankind. The differences between the late 18th century and the modern world seem immense. To contemplate our world as it may exist two hundred years hence sorely taxes our imagination (Figure 6.2).


Figure 6.2 Radical changes on the Earth due to 50 million years of continental drift are
predicted by three University of Chicago paleoclimatologists477


But hundreds or even thousands of years are nothing to the xenologist.143 As biochemist and Nobelist George Wald aptly observes, "in geological time, even one million years is just a day."867 It is inconceivable that all other lifeforms throughout the Galaxy began evolving at exactly the same time as we, and at the same rate. If ETs do exist, many of them undoubtedly possess civilizations millions of years our senior -- if not hundreds of millions or even billions of years more advanced.

Before such numbing timescales, humanity pales into relative insignificance in view of the mission of intelligence in the cosmos. Even if mankind were to be virtually annihilated in some terrible natural catastrophe, over a span of millions of years other mammals might evolve to take up the niche vacated by ourselves. Considering the broad sweep of the evolution of sentience, there seems no reason to doubt that higher intelligence would reassert itself on this planet.

Barring such catastrophes, humanity and its progeny may have literally eons of life and development ahead of it.* The Age of Dinosaurs lasted only a hundred million years, roughly 0.2% the age of the Earth. Says Arthur C. Clarke: "If we last a tenth as long as the great reptiles which we sometimes speak of disparagingly as one of nature’s failures, we will have time enough to make our mark on countless worlds and suns."81

Part of our problem in understanding time is due to the differing order of change in nature (Figure 6.3). Humans are accustomed to dealing with events that can best be classified as "organismic responses" -- instincts and reflexes, learning, cycles of reproduction and so forth.565 We are only now, in the 20th century, becoming dimly aware of the concept of ecological time, the scale upon which demographic (population) and ecospheric changes take place. And the next highest levels -- of evolutionary and geological times -- still remain beyond our ken.


Figure 6.3 Timescales of Responses to Change (from Wilson565)


One interesting example of a long-term trend is the change in the length of day. Every million years, because of tidal friction caused by the Moon, Earth’s day becomes about 3.3 minutes longer.2206 A couple hundred million years ago, during the Age of Dinosaurs, our planet revolved about one hour faster. In the steamy Carboniferous Period, when giant insects cruised forests of giant ferns, the day was only 22 hours long. One eon ago the components of Earth’s air were stabilizing near their present values and marine organisms were reeling with the discovery of sex. But they had to accomplish in only 18 hours what we take 24 to do.

Projecting into the future, a day in 1,000,000,000 A.D. will last about 30 hours. The Earth is gently slowing, a giant top marking time in eons.

"I perceived that I was on a little round grain of rock and metal," wrote Olaf Stapledon in his 1937 science fiction classic Star Maker,

filmed with water and with air, whirling in sunlight and darkness. And on the skin of that little grain all the swarms of men, generation by generation, had lived in labor and blindness, with intermittent joy and intermittent lucidity of spirit. And all their history, with its folk-wanderings, its empires, its philosophies, its proud sciences, its social revolutions, its increasing hunger for community, was but a flicker in one day of the lives of stars.1946

All of these considerations are of great significance to the origin of life on this planet. Until recently, scientists were of the opinion that the creation event itself might have taken place one or two eons after the formation of the Earth. But how much time was really required? As late as the middle of this century, no one really knew the answer to this question. The skeletal fossil record extends back only to the beginning of the Cambrian Period, about 600 million years ago. The Precambrian, comprising the first 87% of our world’s history, remained enshrouded in mystery and ambiguity.

In the last decade or two, improved techniques and several major finds have lifted the veil of ignorance. Scientists now hunt for molecular fossils, traces of the biochemical signatures left behind by the remains of microscopic organisms long dead.1420 The evidence now seems fairly clear that single-celled life existed some 3.4-3.6 billion years ago. (But note Schopf.2369) It is plausible that extremely primitive replicative lifeforms existed for several hundred million years prior to these earliest finds.41

The implication is that life had half a billion years, perhaps even less, in which to assemble itself from nonliving chemical precursors. As two pioneers in abiogenesis research have noted:

There is no way at present to estimate when, during this (first) billion or so years, life arose. Periods of a hundred million years are so removed from our experience that we can have no feeling or judgement as to what is likely or unlikely, probable or improbable, within them. If the formation of the first living organism took only one million years, we would not be very surprised. We cannot even prove that 10,000 years is too short a period.521

The process of biological evolution must have begun as soon as the first living system emerged from the primieval "soup" four eons ago. Early forms of anaerobic photosynthesis probably arose three eons ago, in response to what one scientist has called "the world’s first energy crisis." Energy-laden molecules floating in the seas had become depleted. Photosynthesis allowed organisms to directly tap the power of the sun, which partially solved the crisis.

Unicellular life began to diversify about 2.3 billion years after the formation of the Earth, with the appearance of the first metazoans (multicellular animals).939 Aerobic photosynthesis was invented a short while later, and the concentration of oxygen -- a harmful, poisonous waste product detrimental to most lifeforms in existence at the time -- rose dramatically. In response to this "smog crisis," nature invented organisms able to consume the harmful oxidant and return carbon dioxide, thus detoxifying the air. These efforts were not entirely successful, however: Burning oxygen proved more efficient and made possible the conquest of land.

Perhaps the vastness of time and our place in it can best be illustrated by the chronology in Table 6.1. Earth’s biography is plotted as a series of slow, painstaking steps from the formation of our planet 4600 million years ago up through the present. Truly, man is a mere footnote to history.

Sir James Jeans gracefully surmounts the barriers of temporal chauvinism:

We are living at the very beginning of time. We have come into being in the fresh glory of the dawn, and a day of almost unthinkable length stretches before us with unimaginable opportunities for accomplishment. Our descendants of far-off ages, looking down this long vista of time from the other end, will see our present age as the misty morning of human history. Our contemporaries of today will appear as dim, heroic figures who fought their way through jungles of ignorance, error and superstition to discover truth.2109


Table 6.1 A Brief History of Earth
Geological Era
Period (Duration in Mys -- millions of years)
Length of Day
and Major Events
Archean or
(~1000 Mys)
  H2 CH4, NH3, H2O
(N2 CO, HCl, H2S trace constituents) 
Formation and
of planet Earth 
-- none --
(~2100 Mys)




very highly reducing
solidification &
stabilization of
the crust
    Atmosphere strongly
Oceans filled to
10% their present volume
      Great volcanic activity, granite intrusions, some sedimentary deposition, and extensive erosion      
    Great increase in
N2 production
Oldest dated rocks
(~1100 Mys)
  H2 CH4, NH3, N2
(CO2, H2O, HCN,
H2S as trace
Graphites of possible organic origin

Oldest crustal rocks

"Age of
Unicellular Life"


    Atmosphere less reducing        
      Oceans essentially filled   Onverwacht and
Fig-Tree: Organisms resembling hi blue-green algae (chemical me molecular fossils)
Early ly protozoans
Nonoxygenic photosynthesis
    CO2 rises to
1% of total
      First limestone deposits   Microfossils and bacteria  
    Atmosphere slightly
reducing or
    Bulawayan Group, South Rhodesian limestones   
          Soudan Shale microfossils  
Early Proterozoic
(~300 Mys)
  N2, CO2
(NH3, CH3, H2O, O2 as trace constituents)
    Wealth of evidence of biological activity
Strikingly advanced flora, Macro-fossils remain rare 
"Age of
Primitive Marine Invertebrates"
(300 Mys)
Middle Proterozoic
(~120 Mys)
(~600 Mys)
    Witwatersrand Supergroup, South Africa (microbiota)
Invention and deployment of
      Great sedimentation;
sedimentary rocks extremely thick; repeated glaciations; extensive erosion
  Anaerobic and
oxygenic life
flourish, the former
slowly giving way
to the latter
Gunflint Iron Formation (Canada):
blue-green algae,
flagellates, & fungi
    O2 begins a dramatic rise
CO2 drops to present level
CH4, NH3 vanish
Invention of

oxygenic respiration

    Some volcanic activity  
    Atmosphere oxidizing        
          Primitive aquatic plants,
marine protozoa and
aerobic metazoa




    Atmosphere strongly oxidizing        


Late Proterozoic
(~400 Mys)
  N2  78%
O2  21%
Ar   ~1%
CO  ~0.1%
H2O (trace)

Modern atmosphere established

    Bitter Springs:
blue-green algae,
red algae, fungi,
Mollusks, worms, & other marine invertebrates
(sponges, brachiopods)
Invention of Sex
        Algonkian Ice Age      
          All animal & plant
phyla established 
"Age of
(~375 Mys)
Cambrian (100)   Climate warm; formation of major Paleozoic geosynclines   Spores, tracheids
Trilobites and brachiopods dominant
Spread of land plants Freshwater fish, coral,
Marine arachnids
  Ordovician (75)   Low continents; warm Arctic; extensive land submergence & flooding
  Silurian (25) Devonjan (50)

Carboniferous (75)

  Eocambrian Ice Age

Land rises; mountain building arid lowlands;

21 .7h
Wingless insects;
amphibians, lungfishes,
First reptiles
"Age of Fishes and Land Plants"
  Permian (50)   Climate warm & humid at
first, cooler later
Giant ferns, cool swamps
Large insects, thernlonts
"Age of
Insects and Amphibians"
(~150 Mys)
Triassic (50)   Dry and cool; continental
uplifting, Pangea breakup
Modern insects
First dinosaurs
First mammals 
"Age of Reptiles"
    Jurassic (50)

Cretaceous (50)

  Climate warm, last widespread flooding, shallow inland seas; Alps, Andes, Himalayas, Rockies rose
Giant dinosaurs,
toothed birds
Dinosaurs decline;
first flowering plants
(~75 Mys)
Tertiary (75)   Climate cooler
Quaternary Ice Ace(repeated global glaciation)
  Rise of birds,
higher mammals,
and arthropoids (including the genus Homo)
"Age of Mammals"
  Quaternary (1)    



* Ultimately, we are limited only by the lifetime of our sun. Another 8-10 billion years remain before it flickers and dies, although Earth will probably become uninhabitably hot in 4-5 eons.20,2056 Perhaps by then, humanity will have discovered a new homeland.


Last updated on 6 July 2013