Marc Verha
Tue, Jul-10-07, 06:16
(From New York Times article today)
Some 380 million years ago, a few pioneering vertebrates first
made the leap from water to land. And today, tens of millions
of their human descendants seek summer amusement by leaping
the other way. According to the travel industry, close to 90
percent of vacationers choose as their holiday destination an
ocean, lake or other scenic body of water.
We may have lungs rather than gills, and the weaker swimmers
among us may be perfectly capable of drowning in anything
deeper than a bathtub, yet still we feel the primal tug of the
tide. Consciously or otherwise, we know we're really all wet.
As fetuses, we gestate in bags of water. As adults, we are
bags of water: roughly 60 percent of our body weight comes
from water, the fluidic equivalent of 45 quarts. Our cells
need water to operate, and because we lose traces of our
internal stores with every sweat we break, every breath and
excretion we out-take, we must constantly consume more water,
or we will die in three days.
Thirstiness is a universal hallmark of life. Sure, camels can
forgo drinking water for five or six months and desert
tortoises for that many years, and some bacterial and plant
spores seem able to survive for centuries in a state of
dehydrated, suspended animation. Yet sooner or later, if an
organism plans to move, eat or multiply, it must find a
solution of the aqueous kind.
Life on Earth arose in water, and scientists cannot imagine
life arising elsewhere except by water's limpid grace. In the
view of Geraldine Richmond, a chemistry professor at the
University of Oregon who often talks to the public on the
wonders of water, Mark Twain put it neatest: 'Whiskey is for
drinking; water is for fighting over.'
Behind water's peerless punch, and the reason it rather than
alcohol or any other lubricant serves as the elixir of life,
is the three-headed character whose chemical name we all know:
H2O. Scientists observe that when two atoms of hydrogen
conjoin with one of oxygen, the resulting molecule displays a
spectacular range of powers, gaining the mightiness of a
molecular giant while retaining the speed and convenience of a
molecular mite.
'Water behaves very differently from other small molecules,'
said Jill Granger, a professor of chemistry at Sweet Briar
College in Virginia. 'If you want something else with similar
properties, you'd end up with something much bigger and more
complex, and then you'd lose the advantages that water has in
being small.'
Because of water's atomic architecture, the tendency of its
comparatively forceful oxygen centerpiece to cling greedily to
electrons as it consorts with its two meeker hydrogen mates,
the entire molecule ends up polarized, with slight
electromagnetic charges on its foreside and aft. Those mild
charges in turn allow water molecules to engage in mild mass
communion, linking up with one another and with other
molecules, too, through an essential connection called a
hydrogen bond. The hydrogen bond that attracts water to water
and to other like-minded players is subtler than the bond that
ties each water molecule's atoms together. But subtlety breeds
opportunity, and from hydrogen bonds many of water's major and
minor properties flow.
With their hydrogen bonds, water molecules become sticky,
cohering as a liquid into droplets and rivulets and following
each other around like a jiggling conga line. Such stickiness
means that water is drawn to the inner plumbing of plants and
will crawl up the fibrous conduits to hydrate even the crowns
of redwood trees towering hundreds of feet above ground.
Pulled together by hydrogen bonds, water molecules become
mature and stable, able to absorb huge amounts of energy
before pulling a radical phase shift and changing from ice to
liquid or liquid to gas. As a result, water has surprisingly
high boiling and freezing points, and a strikingly generous
gap between the two. For a substance with only three atoms,
and two of them tiny little hydrogens, Dr. Richmond said,
You'd expect water to vaporize into a gas at something like
minus 90 degrees Fahrenheit, to freeze a mere 40 degrees below
its boiling point, and to show scant inclination to linger in
a liquid phase.
That's what happens to hydrogen sulfide, a similarly sized
molecule but with its two hydrogen atoms fastened to sulfur
rather than to oxygen; on our temperate world, hydrogen
sulfide has long since reached its boiling point and exists as
a foul-smelling gas. Same for the tidy troika of carbon
dioxide: low freezing point, low boiling point, and, poof,
it's up in the air. But given its vivid power of hydrogen
bonding, water proves less flighty and fickle, with a boiling
point at sea level of 212 degrees Fahrenheit, and a full 180
degrees lying between the tempest of a teapot and the tinkling
of an ice cube at 32 degrees. A vast temperature span over
which water molecules can pool and cling as the liquid assets
we love best.
We rely in myriad ways on water's fluid forbearance, its
willingness to take the heat without blinking. Earth's oceans
and lakes soak up huge quantities of solar radiation and help
moderate the climate. As sweat evaporates from our skin, it
wicks away large amounts of excess heat.
Water also serves as a nearly universal solvent, able to
dissolve more substances than any other liquid. It can act as
an acid, it can act as a base, with a pinch of salt it is the
solution in which the cell's thousands of chemical reactions
take place.
At the same time, water's gregariousness, its hydrogen-bonded
viscosity, helps lend the cell a sense of community.
'Water acts as the contact between biological molecules, not
just separating them, but imparting information among them,'
said Martin Chaplin, a professor of applied science who
studies the structure of water at London South Bank
University. 'In an aqueous environment, all the molecules are
able to feel the structure of all the other molecules that are
present, so they can work as whole rather than as
individuals.'
There's no end to water's chemical kinkiness, including the
way it freezes from the top down and becomes buoyant as it
chills. Most substances shrink and get denser and heavier as
they cool, and expand and lighten as they melt. Water bucks
the norm, and is lighter and airier as ice than when liquid,
and so in winter marine life can find liquid haven beneath the
floating blanket of ice, and so in summer ice cubes bob and
clink in your glass of lemonade. Bottoms up.
Some 380 million years ago, a few pioneering vertebrates first
made the leap from water to land. And today, tens of millions
of their human descendants seek summer amusement by leaping
the other way. According to the travel industry, close to 90
percent of vacationers choose as their holiday destination an
ocean, lake or other scenic body of water.
We may have lungs rather than gills, and the weaker swimmers
among us may be perfectly capable of drowning in anything
deeper than a bathtub, yet still we feel the primal tug of the
tide. Consciously or otherwise, we know we're really all wet.
As fetuses, we gestate in bags of water. As adults, we are
bags of water: roughly 60 percent of our body weight comes
from water, the fluidic equivalent of 45 quarts. Our cells
need water to operate, and because we lose traces of our
internal stores with every sweat we break, every breath and
excretion we out-take, we must constantly consume more water,
or we will die in three days.
Thirstiness is a universal hallmark of life. Sure, camels can
forgo drinking water for five or six months and desert
tortoises for that many years, and some bacterial and plant
spores seem able to survive for centuries in a state of
dehydrated, suspended animation. Yet sooner or later, if an
organism plans to move, eat or multiply, it must find a
solution of the aqueous kind.
Life on Earth arose in water, and scientists cannot imagine
life arising elsewhere except by water's limpid grace. In the
view of Geraldine Richmond, a chemistry professor at the
University of Oregon who often talks to the public on the
wonders of water, Mark Twain put it neatest: 'Whiskey is for
drinking; water is for fighting over.'
Behind water's peerless punch, and the reason it rather than
alcohol or any other lubricant serves as the elixir of life,
is the three-headed character whose chemical name we all know:
H2O. Scientists observe that when two atoms of hydrogen
conjoin with one of oxygen, the resulting molecule displays a
spectacular range of powers, gaining the mightiness of a
molecular giant while retaining the speed and convenience of a
molecular mite.
'Water behaves very differently from other small molecules,'
said Jill Granger, a professor of chemistry at Sweet Briar
College in Virginia. 'If you want something else with similar
properties, you'd end up with something much bigger and more
complex, and then you'd lose the advantages that water has in
being small.'
Because of water's atomic architecture, the tendency of its
comparatively forceful oxygen centerpiece to cling greedily to
electrons as it consorts with its two meeker hydrogen mates,
the entire molecule ends up polarized, with slight
electromagnetic charges on its foreside and aft. Those mild
charges in turn allow water molecules to engage in mild mass
communion, linking up with one another and with other
molecules, too, through an essential connection called a
hydrogen bond. The hydrogen bond that attracts water to water
and to other like-minded players is subtler than the bond that
ties each water molecule's atoms together. But subtlety breeds
opportunity, and from hydrogen bonds many of water's major and
minor properties flow.
With their hydrogen bonds, water molecules become sticky,
cohering as a liquid into droplets and rivulets and following
each other around like a jiggling conga line. Such stickiness
means that water is drawn to the inner plumbing of plants and
will crawl up the fibrous conduits to hydrate even the crowns
of redwood trees towering hundreds of feet above ground.
Pulled together by hydrogen bonds, water molecules become
mature and stable, able to absorb huge amounts of energy
before pulling a radical phase shift and changing from ice to
liquid or liquid to gas. As a result, water has surprisingly
high boiling and freezing points, and a strikingly generous
gap between the two. For a substance with only three atoms,
and two of them tiny little hydrogens, Dr. Richmond said,
You'd expect water to vaporize into a gas at something like
minus 90 degrees Fahrenheit, to freeze a mere 40 degrees below
its boiling point, and to show scant inclination to linger in
a liquid phase.
That's what happens to hydrogen sulfide, a similarly sized
molecule but with its two hydrogen atoms fastened to sulfur
rather than to oxygen; on our temperate world, hydrogen
sulfide has long since reached its boiling point and exists as
a foul-smelling gas. Same for the tidy troika of carbon
dioxide: low freezing point, low boiling point, and, poof,
it's up in the air. But given its vivid power of hydrogen
bonding, water proves less flighty and fickle, with a boiling
point at sea level of 212 degrees Fahrenheit, and a full 180
degrees lying between the tempest of a teapot and the tinkling
of an ice cube at 32 degrees. A vast temperature span over
which water molecules can pool and cling as the liquid assets
we love best.
We rely in myriad ways on water's fluid forbearance, its
willingness to take the heat without blinking. Earth's oceans
and lakes soak up huge quantities of solar radiation and help
moderate the climate. As sweat evaporates from our skin, it
wicks away large amounts of excess heat.
Water also serves as a nearly universal solvent, able to
dissolve more substances than any other liquid. It can act as
an acid, it can act as a base, with a pinch of salt it is the
solution in which the cell's thousands of chemical reactions
take place.
At the same time, water's gregariousness, its hydrogen-bonded
viscosity, helps lend the cell a sense of community.
'Water acts as the contact between biological molecules, not
just separating them, but imparting information among them,'
said Martin Chaplin, a professor of applied science who
studies the structure of water at London South Bank
University. 'In an aqueous environment, all the molecules are
able to feel the structure of all the other molecules that are
present, so they can work as whole rather than as
individuals.'
There's no end to water's chemical kinkiness, including the
way it freezes from the top down and becomes buoyant as it
chills. Most substances shrink and get denser and heavier as
they cool, and expand and lighten as they melt. Water bucks
the norm, and is lighter and airier as ice than when liquid,
and so in winter marine life can find liquid haven beneath the
floating blanket of ice, and so in summer ice cubes bob and
clink in your glass of lemonade. Bottoms up.