SOLUTION TO DARWIN'S DILEMMA:
DISCOVERY OF THE MISSING PRECAMBRIAN RECORD OF LIFE

J. WILLIAM SCHOPF

Department of Earth and Space Sciences,
Institute of Geophysics and Planetary Physics
(Center for the Study of Evolution and the Origin of Life),
and Molecular Biology Institute,
University of California, Los Angeles, CA 90095-1567
PHONE: (310) 825-1170
FAX: (310) 825-0097
E-MAIL: Schopf@ess.ucla.edu

In 1859, in On the Origin of Species, Darwin broached what he regarded to be the most vexing problem facing his theory of evolution -- the lack of a rich fossil record predating the rise of the first primitive animals that marks the beginning of the Cambrian Period of geologic time (~550 million years ago), an "inexplicable" absence that could be "truly urged as a valid argument" against his all-embracing synthesis. For more than 100 years, the "missing Precambrian history of life" stood out as one of the greatest unsolved mysteries in natural science. Over the past few decades, however -- after a century of trial and error, search and eventual discovery -- life's earliest history has finally been uncovered as the documented fossil record has been extended to some 3,500 million years ago, an age more than three-quarters that of the planet itself. An immense early fossil record, unknown and assumed unknowable, has been unearthed to reveal an evolutionary progression dominated by microbes that stretches seven times farther into the geologic past than had previously been thought. Life began far earlier, and evidently evolved initially much farther and faster than anyone had imagined. Perhaps the origin of life is "easier" -- and perhaps life itself is cosmically more widespread -- than conventional views have led us to suspect.

PHYSICS AND LIFE

PAUL DAVIES

Imperial College,
London, UK

Is physics relevant to life? Although it is often glibly said that life is written into the laws of physics, most researchers today regard the problem of life as one of organizational complexity, rather than physics. Physics may provide a bio-friendly universe, plus the essential "tool kit" from which suitable replicators arise, but thereafter the principles involved in the emergence and evolution of life are inspired more by information theory and computing than physics. Recently however, developments in quantum mechanics have led to renewed speculation that fundamental physics might after all play a direct role in life. The burgeoning field of quantum computation is providing new insights into the relationship between information, computation and physics, with hints that life may already be exploiting these deep linkages.

EUROPA: PROSPECTS FOR AN OCEAN AND LIFE

CYNTHIA PHILLIPS

Center for the Study of Life in the Universe
Seti Institute, 2035 Landings Drive
94043 Mountain View (California)
United States of America
tel (650)-960-4528
FAX: +1(650) 961 7099
email: phillips@seti.org

Life as we know it depends on the presence of three things: liquid water, certain "biogenic" elements (including carbon, as well as oxygen, nitrogen, hydrogen, phosphorous, sulfur, and others), and a useful source of free energy. Jupiter's icy satellite Europa may meet these criteria, and thus be a possible location for a non-terrestrial biosphere. This talk will summarize the evidence for an ocean of liquid water beneath Europa's icy surface, including theoretical work as well as observational constraints from Galileo imaging, gravity, and magnetic field data. It will also consider the spectral and theoretical evidence relating to Europa's surface composition, and how interaction with charged particles might produce biologically-useful compounds at Europa's surface. Finally, sources of free energy, including the generation of oxidants at Europa's surface and methods for their preservation and introduction into a subsurface liquid water layer, will be discussed.

PEPTIDE NUCLEIC ACIDS RATHER THAN RNA MAY HAVE BEEN THE FIRST GENETIC MOLECULE

STANLEY MILLER

Dept of Chemistry and Biochemistry, 0506
University of California, San Diego
9500 Gilman Drive,
La Jolla, CA 92093-0506
United States of America

Numerous problems exist with the current thinking of RNA as the first genetic material. No plausible prebiotic processes have yet been demonstrated to produce the nucleosides or nucleotides or for efficient two-way nonenzymatic replication. Peptide nucleic acid (PNBA) is a promising precursor to RNA, consisting of N-(2-aminoethyl)glycine (AEG) and the adenine, uracil, guanine, and cytosine-N-acetic acids. However, PNA has not yet been deomonstrated to be prebiotic. We show here that AEG is produced directly in electic discharge reactions from CH4, N2, NH3, and H2O. Electric discharges also produce ethylenediamine, as do NH4CN polymerizations. AEG is produced from the robust Strecker synthesis with ethylenediamine. The NH4CN polymerization in the presence of glycine leads to the adenine and guanine-N9-acetic acids, and the cytosine and uracil-N1-acetic acids are produced in high yield from the reaction of cyanoacetaldehyde with hydantoic acid, rather than urea. Preliminary experiments suggest that AEG may polymerize rapidly at 100°C to give the polypeptide backbone of PNA. The ease of synthesis of the components of PNA and possibility of polymerization of AEG reinforce the possibility that PNA may have been the first genetic material.

ANCIENT LIFE ON MARS AND EARTH

J. WILLIAM SCHOPF

Department of Earth and Space Sciences,
Institute of Geophysics and Planetary Physics
(Center for the Study of Evolution and the Origin of Life),
and Molecular Biology Institute,
University of California, Los Angeles, CA 90095-1567
PHONE: (310) 825-1170
FAX: (310) 825-0097
E-MAIL: Schopf@ess.ucla.edu

In the modern epoch, the question of life on Mars dates from the pioneering observations of the great Italian astronomer Giovanni Virginio Schiaparelli (1835-1910) who recorded the presence of linear features on Mars' surface that were thereafter interpreted by Percival Lowell (1855-1916) -- an influential if somewhat eccentric American astronomer -- as artificial canals, aqueducts built by an advanced civilization to link the planet's icy water-rich poles to its arid equatorial deserts. By 1924, belief in "life on Mars" had become so widespread, so notably pervasive, that in August of that year -- when the orbits of Earth and Mars were especially close -- governments worldwide urged their citizens to turn off their home radios so that supersenstitive receivers could listen during an hour-long period for signals from beings on the Red Planet. Though this attempt, of course, came to naught, and though even to the present day there remains no firm evidence of any type of life on Mars -- past or present, primitive or advanced -- the question of life on the Red Planet has lingered on, lying dormant for years at a time only to rise again in the public mind as it did most recently in August 1996, spurred by NASA's now famous report of possible evidence of "ancient Martian microbes." Though the report first looked promising, it has since failed to meet the test. The late Carl Sagan phrased it well: "Extraordinary claims require extraordinary evidence" and, plainly put, there is still no clearcut evidence, no "smoking gun," to back this extraordinary claim. But it would be wrong to think that the matter is closed, for in truth the question of life on Mars simply remains unanswered -- no more, no less -- a status captured by another telling Saganism: "Absence of evidence is not evidence of absence!" Understanding of the Red Planet is in its infancy; its climate, its range of settings, its history, are all as yet largely undeciphered, and the hunt for life on Mars remains a scientific quest. The tools are at hand. And the rules for the search are very much the same as those used so successfully in tracing life's history on planet Earth. If there once was or is now life on Mars or elsewhere in the accessible reaches of space, science can and will ferret it out.

THE PLURALITY OF WORLDS

FRANCESCO BERTOLA

Dipartimento di Astronomia
Vicolo dell'Osservatorio 5
I-35122 Padova, ITALY
Phone: +39-049-829-3436
FAX: +39-049-875-9840

The debate on the plurality of worlds goes back to ancient Greece. The first speculations are attributed to Democritus. Before the Copernican revolution the meaning of"world" was that of "universe", namely the totality of things. After Copernicus worlds meant mainly earths or planetary systems most of them possibly inhabited. The latest developments of modern cosmology invoke again the existence of an infinite number of universes.