Emergence on Earth . . . and elsewhere?? | Genesis: The Scientific Quest for Life's Origins

A survey of Origins of Life research from a leader in the field | Genesis: The Scientific Quest for Life's Origins | Robert Hazen

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	• Genesis: The Scientific Quest for Life's Origins Robert Hazen Joseph Henry Press, 2007 - 368 pages average customer review:based on 19 reviews view larger image
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highly recommended

A Personal View from a Scientist

Robert Hazen presents a general feeling for what it is like to be a scientist researching the origin of life. The impression one gets is that there are a lot of ideas about abiogenesis, but not much data with which to sort through these possibilities.

Hazen does an good job of presenting the various hypotheses on the relevant concepts. However, he also ends up talking just as much about the personalities engaged in the research as he does talking about the ideas themselves.

Emergence on Earth . . . and elsewhere??

Putting it back to front, Hazen lists the three likely scenarios for life's origins: a chemical process leading to metabolism, a chemical process leading to replication, or a combination of the two. The remainder of the book is an exploration of the ideas centered on the way life was started on this planet and the researchers who have conceived or tested them. The list of scientists involved is extensive, but in this finely crafted work, Hazen is able to introduce them, describe their work - and his own - clearly and effectively. With the advantage of arriving at "Life's Origins" studies from an "outside" discipline - geophysics - the author brings a fine sense of detachment to this presentation.

In any other account on this topic, the opening would inevitably be a reference to Charles Darwin's "warm little pond". The "warm little pond" idea was tested in 1953 by Stanley Miller, who figures significantly in this story. Darwin's "first cell" clearly required simpler precursors to be assembled and put in operation. As an earth scientist, Hazen is more interested in the role played by chemistry and physics than cell biology, and so begins the book with water's changing properties under increased temperature and pressure. This situation plays a more significant role in life's beginnings than we might guess, since one scenario for the initial steps lies deep in the Earth where water, essential to life, lies buried in rocks, hot and compressed. As it turns out, that water is home to living things - microbes that may not reproduce for over a thousand years, as contrasted with the microbes in your gut that reproduce every twenty minutes. It's a major change in scenarios, going from a little pond to the restrictive environment of the Earth's depths, but Hazen shows how each circumstance has contributed to better understanding of how life came to be. Further, the mechanisms are simple enough to be readily applied on any planet with a suitable environment.

The author weaves a number of research accounts into a broad tapestry he calls "emergence". The point of emergence is that there are no great leaps - life had to be built up through a succession of small, cumulative steps. Each step was a chemical process in the proper environment contributing some minimal change that ultimately became what we now call life. Carbon, he reminds us, is the key, but it does little by itself. Water is an essential factor, because its components are essential to building organic molecules. Each of the steps, so far as they are known, are described and fit into the role of life. More important, and in a significant departure from many books on this topic, Hazen describes the laboratory experiments that have verified suppositions or raised new possibilities about life's formation. Field work is not ignored here. The author describes the discovery of life around sea-floor vents and the implications of the Murchison Meteorite - which delivered dozens of types of amino acids - those famous "building blocks" of life to an Australian paddock. How do these highly diverse scenarios merge to produce the trees, pet turtles and people around us we see today?

That's what remains to be revealed. The gaps in the processes leading to the first true cell must be closed with descriptions of how various components came together. Many researchers have contributed to resolving those "hows" [there's more than one], and it's in this area that Hazen's three-option conclusion is so significant. For most organic chemical processes to take place, the operation requires protection from interference - a surrounding defensive environment. How does a complex carbon molecule build a protective "shell" while it's busy with its own affairs making new compounds? If the shell already exists - and those lab experiments now demonstrate how that can happen, how does the carbon assemblage break in and take sanctuary from a hostile world? Teasing out the answers to these questions has been the work of many scientists, particularly over the past couple of generations.

Life's origins researchers are an irascible lot, sometimes. It's a bit discouraging to read that Stanley Miller, who broke new ground [or perhaps not - German Walter Löb had performed similar work decades before], by generating amino acids in a flask, dismisses the notion of sea-floor vents generating life-promoting processes. And former astronomer Thomas Gold inexplicably rejects any contribution from space to the establishment of life here. The most compelling anecdote in this book however, is of an almost overage PhD student who works out how organic molecules can use - or adapt - the methods rocks use making in crystals. Nick Platt considers this establishes the underlying conditions needed for those molecules which "stack" in layers to create areas leading to the formation of "an information-rich molecule" - RNA, then DNA . Hazen negotiates these troubled conceptual waters with assurance, providing us with a compelling story - or set of stories - relating our beginnings. [stephen a. haines - Ottawa, Canada]

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A survey of Origins of Life research from a leader in the field

Hazen surveys then-current ideas and research on the origins of life. He makes considerable effort to keep it exciting and personal by including stories of research as it happens. I especially appreciated the non-magical discussion of emergence in early chapters; it is a phenomenon which unfortunately is used as an excuse by some to hide or inject magic into the process. Hazen reviews what has been done and what has not been done in the exploration of various ideas about prebiotic chemistry, the RNA World theory (which is accepted by most biologists today) and current cellular life, and attempts to bridge the various stages. The book may leave the reader with the impression that the field is rather chaotic with huge scientific challenges remaining, since Hazen does not come to many conclusions. Unfortunately this impression seems to be accurate. Perhaps young proto-scientists should view this in a positive light: there is still a lot of scientific discovery remaining.

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An interesting book for the layman about an exciting scientific question

As Robert Hazen explains, the complexity we see in the world is not at odds with the Second Law of Thermodynamics. What happens is that in the presence of an energy flow, patterns form in systems which help dissipate that energy.

We need complexity and patterns for life to evolve. Once life begins, evolution can produce more and more complex life forms. But how do we get to the first life form? As the author says, we need prebiotic evolution. Three scenarios are considered. One is that metabolism came first, and that once started, chemical evolution led to replication and membranes. Another is that replication came first, either RNA or a precursor. And the third is that life began as a cooperative phenomenon arising between metabolism and genetics. Hazen seems to like the third possibility, but he does not pick any. I'll pick an option, however: I like the first one. Life reduces carbon dioxide, and I like the idea of chemical evolution getting started once some rudimentary sort of metabolism existed.

The author tells us about some of the specific metabolism-first models. An early one was Sidney Fox's protenoid model. This model was popular at first, and it has been challenged in more recent times, but I think it is worth studying. Another idea Hazen covers is Christian de Duve's "Thioester World." However, de Duve fails to specify the exact chemistry he has in mind to get to life in this manner. Again, I think de Duve's ideas merit serious study. And the final of the metabolism-first ideas is Gunter Wachtershauser's Iron-Sulfur world. This is pretty specific: hydrothermal vents contain carbon dioxide, water, ammonia, hydrogen sulfide, and energy. This is an autotrophic model: the prebiotic structures manufacture their own nourishment rather than simply obtain it from some sort of prebiotic soup. My wild guess is that this is the wrong track: life led to RNA, and I think such delicate molecules as RNA would be tough to produce in such an environment. In addition, we'd need better evidence for specific metabolic cycles that are consistent with this model. But once again, I think these ideas merit careful study.

Next, we read about the "RNA world." RNA is indeed a very special molecule. Once it exists, it can replicate and it can make proteins. That suggests that replicators may have come "first," maybe with a precursor to RNA and then RNA itself. I don't quite buy this argument, because I do not see how we go through chemical evolution to produce something as complex and delicate as RNA without a succession of metabolizing structures which incrementally improve.

Hazen then discusses what sort of replicators must have preceded RNA. Perhaps some PNA (peptide nucleic acid)? We get to read about some a very speculative idea: a "PAH world" (PAHs are polycyclic aromatic hydrocarbons). I think this is very interesting: the idea is to come up with something much more resilient than RNA even if it is far less efficient as a replicator.

Are we getting closer to figuring out the rough process by which life originated? Well, maybe so. But I think we have a very long way to go. On the other hand, that's one of the things that makes this field so exciting.

I recommend this book.

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Theories of life's origins

Hazen surveys the theories of life's origins, organizing them by the stage of producing life to which they pertain, the creation of: biomolecules (e.g. simple amino acid); macromolecules; self replicating systems. Unfortunately, theories are not neatly packaged like that, and Hazen is not all that disciplined about when to present material; for example, he does not like to break up a discussion of a scientist's work, except for his own. In fact he would rather sequentially discuss different theories than to attempt a synthesis, taking a kind of an historical approach. Still, he usually writes clearly, and recapitulates frequently, so while I didn't come away with as firm a grasp of the material as I would like, I enjoyed the book a lot, and am eager to read another good book on the subject. I exclude the section on emergence, which could have been mostly eliminated, and certainly been much better written.

I was most surprised by the fact that there are all kinds of sources for biomolecules, including outer space. Also, rocks and minerals can potentially play multiple roles in the emergence of life: providing energy, catalyzing reactions, concentrating biomolecules selectively, and even, as clay particles, promoting the multiplication of lipid vesicles and the incorporation of RNA into these vesicles. One of the most intriguing theories is one of the newest: that the pyruvates, biomolecules which are abundantly formed even in the absence of life, can form a kind of scaffolding to collect the bases which are the key components of RNA. It is not then too big a jump to think the bases might link and forma proto RNA, and we know RNA can catalyze energetic reactions as well as its own duplication.

One advantage of the historical approach, is that the reader develops a healthy skepticism, to mirror Hazen's. Hazen describes important failures as well as successes. I was greatly surprised to learn that the proportion of light carbon to heavier carbon in a molecule cannot be used as a guaranteed indicator that the molecule was created by a life form. Also, unlike most authors, Hazen, despite being a positive, relatively humble person, does not mind being critical of other scientists, especially those with big egos, and those willing to abuse graduate students.

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Life on Earth arose nearly 4 billion years ago, bursting forth from air, water, and rock. Though the process obeyed all the rules of chemistry and physics, the details of that original event pose as deep a mystery as any facing science. By what process did life actually begin? How did non-living chemicals become alive? Where, when, and how did life emerge on the blasted, barren face of our primitive planet?

Author Robert Hazen is one of the world?s foremost scientists seeking answers to these questions. As an astrobiologist at the Carnegie Institution in Washington, D.C., Robert Hazen has spent many years dealing with the fundamental mechanisms of life?s genesis. As an active research scientist, he is experimentally tracing the spellbinding sequence of events that led to the complicated interactions of carbon-based molecules.

Conducting experiments that subject the mix of elements found near deep-ocean vents to the high temperatures and crushing pressures of those lightless depths, he hypothesizes that life may well have begun in such a place, nourished by a rich mixture of minerals and organic compounds and energized by geotectonic forces. Other scientists believe that life may have originated on Earth?s surface, where ocean waves repeatedly lapped a rocky shoreline. Theories abound. But with Hazen as our guide, we are witness to the first, tentative steps towards life, then privy to the breathtaking drama that rapidly unfolds.

Genesis throws the debate over life?s origins into brilliant relief, tracing the efforts of scientists all over the world as they confront nature?s most enduring mystery. We are taken out of the lab and into the field to meet the key players, witness the debates, and participate in the discoveries and disappointments that are leading inexorably to a plausible explanation for the momentous beginning of life. The theory of emergence is poised to answer a multitude of questions ? even as it raises the possibility that natural processes exist beyond what we now know, perhaps beyond what we even comprehend. Genesis tells the tale of transforming scientific advances in our quest for life?s origins. Written with grace, beauty, and authority, it goes directly to the heart of who we are and how we got here.

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