I spent an enjoyable day with my daughter earlier this year in quest of sand grains around the upper reaches of the Chesapeake Bay, and it turns out that we were following in the footsteps of Robert Hazen. Also in common with Hazen, I find the idea of everything that we don’t know more exciting than what we do, and I play the trumpet (assuming a broad definition of the word “play”). But there the similarities end – Hazen does fundamental and extraordinary science and plays the trumpet professionally. Senior Research Scientist at the Carnegie Institution of Washington’s Geophysical Laboratory and the Clarence Robinson Professor of Earth Science at George Mason University, Bob Hazen was interested in sand grains in the Chesapeake because of the patterns they form when energized by waves, and how these phenomena relate to the origins of life on Earth.
The work of Hazen and his colleagues is breathtaking in its scope and groundbreaking in its implications. They have just made the news – even reported in The Economist – with their idea that, over the Earth’s 4.5 billion year history, minerals have evolved (see Eureka alert ). Not, of course, in exactly the same way that life has evolved, but in a way that intimately ties organic and inorganic evolution together. They describe how perhaps two-thirds of the more than 4,000 known types of minerals today are directly or indirectly linked to biological activity, and how the meager mineralogical diversity of the early Earth was boosted, in just the same way that biodiversity was, by primitive microbes ridding themselves of toxic oxygen, the development of oceans, and plate tectonics (which, it seems, may have begun much earlier than we thought – see Eureka alert). It’s not just the minerals of coral reefs and oysters, but the exotic products of plant roots and microscopic life in alkaline lakes and other extreme environments.
This collaboration between the realms of what we choose to define as the organic and the inorganic is something that has long fascinated Hazen. He has, by some standards, radical views on the development of the first life on Earth, dismissing the generalities of the “primordial soup” (which were once more being bandied about on British TV this week) and the throwing up of scientific hands at a problem that is just too remote and essentially unknowable. In answer to his own provocative question of how geochemistry turned into biochemistry, Hazen applies his belief in the principle that “life is a cosmic imperative,” driven by simple rules in the way nature works to generate complexity. Hence his interest in Chesapeake Bay sand grains.
He sees “emergent complexity” as a fundamental characteristic of many natural systems that are made up of large numbers of individual components, or agents, which together are capable of producing far more complex phenomena than they can on their own (like the sandbanks of my first post). In his own words, “I think the most compelling scenario for life’s origins is based on the concept of emergent complexity. We observe, over and over in nature, when lots of objects, lots of particles, like sand grains or stars or molecules, or cells, when they interact, they tend to yield structures that are far more complex, that have behaviors that are far beyond anything that the individual sand grain, or star, or cell, could do itself. This kind of emergent complexity is the key to understanding the origin of life. The origin of life was a sequence of emergent steps. First, lots of small molecules came together to form larger molecular structures, structures that were able to condense and form structures like cell membranes, and so forth. And then, some of those molecules actually began to self–replicate – groups of molecules making copies of themselves, and therefore growing at the expense of all of the surrounding atoms and molecules and using energy from their environment. And ultimately, that self–replicating system, the emergence of that system led to the kind of competition and natural selection that drove the evolution into the first cells and beyond.”
Take large numbers of individual components – for example, sand grains – energize them – for example with waves or wind – and complex patterns emerge. “I have spent a lot of time thinking about this while walking on the Chesapeake Bay where there is a smooth, slippery kind of rock called blue marl. It has small amounts of sand coating parts of it. You can watch as the wave action laps across these sand grains. What I’ve done is measure [the density of] these sand grains.” Hazen found that as the number of sand grains per square centimeter increased, patterns of increasing complexity developed. The most complex and organized state was reached at a density of about 10,000 sand grains per square centimeter, when the sand formed highly ordered ridges with darker grains concentrated along the top. But when the density increased by a factor of 10 to about 100,000 sand grains per square centimeter, no new structure appeared (AAAS). Sand is a granular material and granular materials indulge themselves in all sorts of bizarre behaviors, many of which demonstrate emerging complexity (some of which will be the subject of a future post). Just look at these examples of patterns formed simply by vibrating sand grains (photos courtesy of Paul Umbanhowar). The dishes at the top are around 12 cms across, each hexagon approximately 0.6 cm. They seem strangely organic. Which they are not, of course, but are these examples of emergently complex patterns, of frameworks and architectures, within which geochemical molecules might have “evolved” into biochemical ones?
Hazen also works on the ways in which complex systems might emerge on the surfaces of individual mineral grains – did the distinctive surface topography of individual sandgrains within these larger-scale systems provide the templates for the “cosmic imperative”? Zachary Adam, an astrobiologist at the University of Washington, has recently suggested that radioactive sand grains in beaches of the early Earth could have provided the chemical energy to assemble the building blocks of cells into the complex molecules of life – could radioactivity be another source of energy to drive Hazen’s emergingly complex systems? (New Scientist)
The ideas of Bob Hazen and his colleagues on organic and inorganic evolution and the intimate relationships between geochemistry and biochemistry have implications far beyond our own Earth and our own origins. "For at least 2.5 billion years, and possibly since the emergence of life, Earth's mineralogy has evolved in parallel with biology," says Hazen. "One implication of this finding is that remote observations of the mineralogy of other moons and planets may provide crucial evidence for biological influences beyond Earth." Phoenix may not have found little green microbes (previous post), but is the mineralogy of life to be founds in its scoops of Martian sand?
[Robert Hazen is a polymath and a Renaissance man. In addition to his research, he is widely respected in science communication, for his thoughtful views on the interfaces between science and religion, and for his music. He is the author of more than 230 articles and 17 books on science, history, and music, including Genesis, The Scientific Quest for Life's Origins. See his webpages for details and downloadable pdf’s of both research and “General audience science writing” – I particularly enjoyed Creation myths: What scientists don’t and can’t know about the world, available here ]