Open Questions: Origins of Life

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Introduction

What is life, anyway?

RNA or proteins?

Alternative scenarios

The first cells

Energy production

DNA and the genetic code

Recommended references: Web sites

Recommended references: Magazine/journal articles

Recommended references: Books

Introduction

Problems about "origins" are always difficult ones in science, for a variety of reasons. Origin events tend to be unique. We can't usually observe them repeatedly. In fact, if the event happened only once, in the distant past, there were not even human observers at the time. Sometimes there is at least evidence of the event that we can observe and study, but sometimes there isn't even that -- especially in the case of the origins of life. And of course, we are usually in even less of a position to perform realistic experiments on origin events to test hypotheses. Sometimes we can perform simulations, either physically or with the assistance of computers, but these have to be based on guesses about the relevant conditions. And even if the simulation has positive results, it can only tell us how the origin event might have happened.

As noted, as far as the origins of life are concerned, we have very little physical evidence to go on. And we can only make guesses about what conditions on Earth were like when life first appeared.

We know more about the origins of the universe itself. We can actually "see" (with suitable instruments) what the universe looked like at an age of about 300,000 years -- in the form of the cosmic microwave background. Our vision of what the Earth was like at a similar age is much less clear. We also have physical evidence of what the universe was like when it was only minutes old, in the form of the relative abundances of a few light elements. All the deuterium that exists today was created at that time and is tangible evidence of prevailing conditions. We even have reliable physical theories (the "standard model" of particle physics) which allows us to infer what the universe was like when it was only a small fraction of a second old.

We have none of this, neither good evidence nor theory, to deduce what conditions on Earth were like when life appeared. Hence it's quite likely that this origin question isn't going to be settled in the near future.

Site indexes

Sites with general resources

Energy Flow and the Organization of Life: This is a working paper by Harold Morowitz and D. Eric Smith supporting their hypothesis that the appearance of life on any sunny, wet, rocky planet is almost a physical necessity. "Life is universally understood to require a source of free energy and mechanisms with which to harness it. Remarkably, the converse may also be true: the continuous generation of sources of free energy by abiotic processes may have forced life into existence as a means to alleviate the buildup of free energy stresses."
The Geochemical Origins of Life: The site presents the theories of Michael J. Russel and Allan J. Hall on the origins of life. They believe that "a major geological process, the cooling by seawater of rocks under the floor of the ocean, played an important role in the origin of life." A statement of their theory is here, and a summary of non-specialists is here.
Supramolecular Chemistry: Home page of research group led by Pier Luigi Luisi. "There are two main research areas in the group: one is the self-assembly and self-organization of macromolecular surfactant aggregates (in particular lipids) and the relevance of these assemblies - micelles, vesicles and liposomes - as models for biological membranes and cells, while the other focuses on polypeptides and the question as to the origin of their structural order, in particular the origin of their homochirality and of their primary sequences and folding." The research page provides more information about current research projects.
Stephen J. Mojzsis: Personal page of researcher involved in discovery of ancient carbonaceous material in Greenland. Contains links to relevant publications in PDF format. Another version of the page is here.
Gustaf Arrhenius' Home Page: Arrhenius' research focuses on reconstructing "possible pathways toward life on Earth by model experiments, which are guided by geophysical and geochemical constraints". Includes abstracts of recent publications.

Surveys, overviews, tutorials

Origin of life: Article from Wikipedia. See also RNA world hypothesis, Miller experiment, Proteinoid.
The Extraordinary Ecosystems of Enceladus: April 2008 article from NASA's Astrobiology Magazine, by Chris McKay and Dennis Matson. Discusses three type of terrestrial extremeophiles and the implications for the origins of life and the possibility of life on Enceladus.
Astrobiology and the Origins of Life: Very good overview lecture by Stanley Awramik, at the BioForum site. The emphasis is really on the origins of life on Earth, rather than astrobiology in general.
Evolution and diversity of cells: Some brief notes about issues related to the origins of life.
Catastrophe, Mother of Evolution: Life Survived Early Bombardment: December 2000 article from Space.com. Discusses recent evidence of biological activity in rocks 3.85 billion years old.
Greenland Rocks Tell New Tale of Life on Earth: March 1997 article from NSF Frontiers about the discovery of life-related carbonaceous material in 3.85 Ga rocks from Akilia Island in Greenland.
Life on Earth began at least 3.85 billion years ago: NASA press release on the Akilia Island carbonaceous material discovery.
Isua Multidisciplinary Research Project - Description: Background information on the Isua Greenstone Belt of Greenland, in which evidence of ancient carbonaceous material has been found.
Evidence for Life on Earth More Than 3850 Million Years Ago: Article on ancient carbonaceous material in Greenland, by Heinrich D. Holland
Vestiges of a Beginning: Clues to the Emergent Biosphere Recorded in the Oldest Known Sedimentary Rocks: Very informative April 2000 article by Stephen J. Mojzsis and T. Mark Harrison on earliest chemical evidence of life.
Evidence for Earliest Known Life on Earth: Brief page about the Greenland rock containing eividence of ancient life.
Pursuing Life on Two Frontiers: November 9, 1996 article from Science News on Greenland evidence of ancient life.
Cooking 101: Very informational Science Notes article by Catherine Zandonella on the chemistry of the first "living" molecule.
A Simpler Origin for Life: February 2007 Scientific American In Focus article, subtitled "The sudden appearance of a large self-copying molecule such as RNA was exceedingly improbable. Energy-driven networks of small molecules afford better odds as the initiators of life."
The Raw Materials: March 1999 Scientific American Explore article, subtitled "The chemistry of life is an integral part of the process that births stars." About the interstellar formation of organic compounds.
Life, Life Everywhere: November 1996 Scientific American Explore article, subtitled "The origin of life on earth appears more and more inevitable--or does it?."
Origins of Life: Very brief overview of a few aspects of how life may have originated.

Recommended references: Magazine/journal articles

Are Aliens Among Us?
Paul Davies
Scientific American, December 2007
It Came from Outer Space
Joe Alper
Astronomy, November 2002, pp. 36-41: Evidence from radio astronomy and the study of a few meteorites which contain a diversity of organic compounds suggests that these compounds are routinely synthesized in interstellar space. Arriving on Earth in grains of dust, they may have provided the raw materials for life here and elsewhere.
An Argument for the Cometary Origin of the Biosphere
Armand H. Delsemme
American Scientist, September-October 2001, pp. 432-442: Evidence increasingly suggests that comets brought much of Earth's atmosphere and water, as well as organic molecules, during the first 600 million years after the planet formed. This would have provided the raw materials for the origins of life.
[Abstract and references]
Life's Rocky Start
Robert M. Hazen
Scientific American, April 2001, pp. 76-85: Life on Earth must have originated as a chemical event. Crystalline surfaces of certain minerals may have provided a scaffolding for the construction of biological molecules.
Cosmic Chemistry Gets Creative
Jessica Gorman
Science News, May 19, 2001, pp. 317-319: All the chemical compounds necessary for life seem to exist in space. The possibility that life may have started from such compounds that arrived on Earth on a comet, meteor, or dust.
Uprooting the Tree of Life
W. Ford Doolittle
Scientific American, February 2000, pp. 90-95: Just 10 years ago biologists thought they had worked out how the earliest cells evolved. Since then, studies of ribosomal RNA have indicated a more complex theory may be needed. It is possible that prokaryotes, archaea, and eukaryotes arose somewhat independently from more primitive types of cells.
Polarized Starlight and the Handedness of Life
Stuart Clark
American Scientist, July-August 1999, pp. 336-343: Chiral molecules such as amino acids and sugars are generally found in only one of their enantiomeric forms in terrestrial life. The explanation for this may be traceable to circular polarization of starlight in space.
Life's Far-Flung Raw Materials
Max P. Bernstein; Scott A. Standford; Louis J. Allamandola
Scientific American, July 1999, pp. 42-49: Complex organic molecules are abundant in interstellar clouds. Such molecules that survived the formation of the solar system may have given rise to life on Earth.
The Beginnings of Life on Earth
Christian de Duve
American Scientist, September-October 1995, pp. 428-437: Life began on Earth about 4 billion years ago through a long succession of chemical steps. In spite of the complexity of the process, the outcome in the form of life as we know it may have been almost inevitable from the existing conditions.
Synthetic Self-Replicating Molecules
Julius Rebek, Jr.
Scientific American, pp. 48-55: One approach to research into the origins of life is to try to recreate important biological molecules by simulated natural processes. An alternative is to experiment with self-replication in carefully designed but non-biological molecules.
Handedness, Origin of Life and Evolution
Valdik A. Avetisov; Vitalii I. Goldanskii; Vladimir V. Zuz'min
Physics Today, July 1991, pp. 33-41: The physics of symmetry breaking may shed some light on the origins of life. Proteins are constructed only from left-handed amino acids, while DNA contains only right-handed sugars. This could be an important clue to how such biological molecules originated.

Recommended references: Books

Christopher Wills; Jeffrey Bada -- The Spark of Life: Darwin and the Primeval Soup
Perseus Publishing, 2000: Wills and Bada present theories of the origins of life from a historical perspective. Their own theory is that life originated in a chemical process of natural selection on the Earth's surface. They consider the implications for the existence of life elsewhere in the universe.
Iris Fry -- The Emergence of Life on Earth: A Historical and Scientific Overview
Rutgers University Press, 2000: As the subtitle suggests, a historically-oriented overview is presented of a variety of theories about the origins of life. The possibility of life on other planets is considered.
Noam Lahav -- Biogenesis: Theories of Life's Origins
Oxford University Press, 1999: The author presents a more detailed and technical account of current theories of the origin of life than is attempted in most books for a general audience. The book is in four parts: the history of enquiries into the origins of life, the basic biological facts that need to be accounted for, the "arena" in which life emerged, and the varieties of theories which try to explain the emergence of life.
Freeman Dyson -- Origins of Life
Cambridge University Press, 1999: In this short book Dyson focuses on two essential characteristics of "life": replication and metabolism. He outlines the two types of theories of life's origin: those which assume replication came first (the majority) and those which assume metabolism was first.
André Brack, ed. -- The Molecular Origins of Life: Assembling Pieces of the Puzzle
Cambridge University Press, 1998: This is a collection of papers by a number of experts in the subject. Most papers present detailed accounts of the ancient environments in which life could have arisen and of possible chemical pathways leading to life.
Harold J. Morowitz – Beginnings of Cellular Life: Metabolism Recapitulates Biogenesis
Yale University Press, 1992: Morowitz offers a relatively brief monograph that sets out his own views of how cellular life came about. In his model, cells originate first, followed by proteins, with genes coming last. Much attention is given to the biochemistry hypothesized to be involved in the origins of life.
Christian de Duve – Blueprint for a Cell: The Nature and Origin of Life
Carolina Biological Supply Company, 1991: de Duve, a Nobel laureate, lays out in technical but comprehensible details the essentials of cell biology and how it could have originated. The first half of the book covers the elements of cell biology, while the second explores the physics and chemistry that could have led to the origin of cells.
A. G. Cairns-Smith -- Seven Clues to the Origin of Life
Cambridge University Press, 1985: The question of how life may have arisen on Earth is addressed in the spirit of a detective story. The author eventually develops his theory that clay played an essential role in the chemical reactions that led to life.

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