The Peculiar Properties of Ice - Evolution News & Views

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The Peculiar Properties of Ice

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Water is an odd little molecule. Liquid water is abundantly available here on Earth, but it's elusive in other parts of the universe. Liquid water is vital to life's existence, but it only exists in a limited range of temperatures and pressures. Solid and gaseous states are much more abundant. Conveniently, Earth happens to have the appropriate temperature and pressure range to host water in all of its phases.

One of water's many strange properties is that its solid state is less dense than its liquid state. With most compounds, it is the other way around. We see this property every day. The ice cubes in your glass of water float, rather than sinking to the bottom of the glass. This property may not sound very impressive, but it has important implications for life on Earth. When lakes and oceans freeze, the frozen water remains on top, allowing abundant sea life to exist in the water below. Furthermore, because ice does not sink to the bottom of lakes or the ocean, the sun's rays will eventually melt the ice during the warmer parts of the year. This would not be possible if water behaved as most substances do.

Ice itself has many interesting properties, particularly the way it crystallizes. Researchers are still studying the way water crystallizes into ice. Wilson Bentley was the first to photograph ice crystal structures, otherwise known as snowflakes. He determined that snowflakes usually have six prongs (or axis of symmetry) although some have four. He also concluded that each ice crystal is unique, a lesson that many of us learned in grade school thanks to Bentley's extensive studies on snowflake morphology.

However, as it turns out, there are many other types (or phases) of ice than just the typical snowflake or ice cube that we are used to seeing, although these phases are difficult to find naturally and are typically made in the lab. These different phases are formed by subjecting ice to various temperatures and pressures, causing a change in the crystal structure. For those familiar with chemistry, some of these phases have ordered oxygen atoms but disorded hydrogen packing. Other ice phases have areas of order amid disorder, or "localized order."

The study of the properties of ice from various sources, both terrestrial and stellar, is now a thriving area of research. Thorston Bartels-Rausch and colleagues wrote a sixty-page review article, "Ice structures, patterns, and processes: A view across ice fields," in ArXiv. In it they discuss the many areas of ice research as well as research questions that still remain to be explored. This article delves into everything from basic molecular packing structures, to ice in outer space (astrophysical ice), to atmospheric ice, to sea ice, all of which have remarkably varied properties. It is an interesting article that brings together diverse fields of ice study pointing to new possible lines of research on avalanche prediction, the composition of comets, climate change, and the origin of life.

These ice studies have implications for evolution and intelligent design. First, sea ice is quite sensitive to changes in temperature and pressure. This does not mean that ice will melt easily; on the contrary water requires quite a bit of energy to change from one phase to another. That's another important requirement for maintaining life on Earth. The authors indicate that the crystalline properties of ice are sensitive to temperature and pressure changes. They speculate that this is perhaps why the origin of life would likely occur in sea ice rather than in a hot environment:

Owing to its being a multiphase system, sea ice reacts under small temperature variations with strong property changes. In this way sea ice renders many conditions and processes conducive to the generation of life...
As we reported here, there are some fundamental problems that still need to be addressed for an ice-packed origin of life to be feasible. A cold origin-of-life scenario may seem to solve some difficulties with molecular stability and nucleotide concentration, but the tradeoffs, including a slower reaction rate, make this scenario untenable.

Rather than sea ice as a possible origin of life, the authors also point out that cometary ice studies are important because chemicals that are typically necessary for the formation of amino acids and nucleotides have been found in such ice. They speculate that perhaps the molecules necessary for the formation of RNA were brought to Earth inside a comet, and seeded the origin of life. This may or may not be the case, but it only transfers the question of "how did life begin" to a different location while leaving unaddressed the inherent problem of information arising from merely chemical mechanisms.

The second implication for evolution and intelligent design is that ice's properties seem eerily well suited to allow life to thrive on Earth. Ice is less dense than liquid water, allowing abundant sea and ocean life to survive cold temperatures, as mentioned above. Water, in all of its phases, has a remarkably high heat capacity, which means that it does not heat up or cool down very quickly. This plays a role in moderating temperature extremes on Earth as well as maintaining oceanic life.

Lastly, Earth's being in just the right temperature and pressure range for all three phases of water to exist allows for the formation of ice cores, a kind of natural time capsule. Ice cores have made possible the discovery of many aspects of Earth's history, including past climate change, nearby supernovae, and volcanic eruptions. It's another of the suite of favorable conditions that, as Richards and Gonzales argue in Privileged Planet, allow for life but also for human scientific investigation.


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