Alan Stahler: Distilleries everywhere
August 22, 2018
Our planet Earth is a gigantic distillery … distilling, not booze, but metals and minerals and water.
The rocks and minerals we find in the foothills are different from those in the Coast Ranges … and there's gold in them thar foothills … all thanks to distillation.
Look toward Mars (close to the moon tonight). Mars, too, was once a distillery, but is it still? As you look toward Mars, you're also looking toward a spacecraft, now halfway between Earth and Mars.
The first interplanetary spacecraft to launch (last May) from California, will look for evidence that present-day Mars is a still a distillery.
Yeast, fermenting sugar to make wine and beer, excrete ethanol (ethyl/grain/drinking alcohol) as a waste product. But ethanol is toxic — it's the active ingredient in many "sanitary wipes."
Toxicity limits how much ethanol yeast can pee into their bathwater. Twelve percent seems to be about max. Not coincidentally, wine is twelve percent alcohol.
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Suppose you want a stronger concoction. Water boils at 212 degrees Fahrenheit, ethanol at 173 degrees — almost 40 degrees cooler. Put a pot of wine on the stove, heat it up, and the ethanol will boil before the water.
Collect the vapor rising from the brew, cool it down to condense it back to liquid, and you've got brandywine … burn wine … brandy.
Most of the substances in the soil and the oceans don't evaporate easily, but water does. Gaseous water — water vapor — rises into the sky, where it cools, condenses to form cloud droplets, and then rains down. The atmosphere thus distills pure water from sea and soil.
The highest clouds we commonly see are "mares' tails." Wispy cirrus ("hair") clouds tell us that it's cold up there. Cirrus are made of crystals of ice — not frozen water droplets, but ice that formed as water molecules latched onto one another to build crystals, without ever going through the liquid state.
Ice forms at the Martian poles, north and south, in the same way — it never rains on Mars. But the Martian poles are so cold, another type of ice also forms, molecule-by-molecule.
The thin Martian atmosphere is almost entirely carbon dioxide. When winter reaches one of the Martian poles, it gets so cold that carbon dioxide forms a layer of "dry ice" over the water ice.
Enough carbon dioxide turns to ice that atmospheric pressure drops. (When the moon again goes dark, local astronomers will set up scopes for the public; we expect to see one or both of the Martian polar caps.)
Miles beneath our feet, temperatures climb high enough to melt minerals in rock … but not all the minerals. Down below, another distillery is at work.
When molten minerals make their way to the surface, they may erupt from volcanoes. If they don't make it quite to the surface, they may slowly solidify — slowly enough to grow large crystals.
The granitic rocks of the foothills solidified down below, later to be uncovered after the miles of rock above had eroded away. Granitic rocks are made of minerals that melt at fairly low temperatures (a thousand-plus degrees Fahrenheit, or so).
The volcanoes of Hawaii erupt minerals that melt at higher temperatures — 2,000 degrees or so — and form different sorts of rocks.
When water is hot, and under pressure, it can dissolve an amazing variety of substances — substances like gold, and quartz. Heat and pressure and water, together, create the rock-distilleries beneath our feet.
A volcano is thus excellent evidence that distillation is occurring.
The first spacecraft to orbit Mars discovered volcanoes, but with no evidence of having erupted recently. Is Mars still distilling its rocks or is it a dead planet?
The spacecraft, now halfway there, will set down on Mars on the Monday after Thanksgiving.
Alan Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at firstname.lastname@example.org
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