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Speed of scent, end of world, Alces alces

Q: What is the speed of scent? If sharks can smell at great distances, how fast does the scent of blood or anything else travel in water or air? What permits scent to travel in water? — Michael, Washington, D. C.

A bluefin tuna attacked by a shark while being reeled in. [Jose Cart, NOAA]

A: A bluefin tuna strikes the baited hook. Blood flows.

The blood slowly spreads out in the still sea. Minutes pass. In perfectly still water, the odor molecules randomly bop against one another and nearby water molecules. Gradually, the blood molecules move apart and eventually a few of the billions of jostling molecules bumble their way to a shark’s nose.

Those few blood molecules are enough. A shark’s sense of smell is 10,000 times more acute than a human. She can detect half a pinch of amino acids (the basic ingredient of blood) dissolved in a large swimming pool of water mixed with 92 tons of salt! The shark closes fast as angler and tuna struggle. The shark attacks! Soon, little tuna remains.

How long does it take for the blood to diffuse through the sea? The warmer the water temperature, the faster the diffusion. The more blood, the faster it scatters. How fast the blood molecules migrate through the sea also depends on the speed and direction of sea currents.

Random movements of the blood molecules, however, take significant time because they don’t travel far before they collide with another blood or a water molecule. That’s why we stir coffee with a spoon to speed the motion of sugar molecules. Food coloring dropped into a glass of water takes minutes to disperse throughout the glass.

Odors waft through air much faster than they do through water because an odor molecule’s free path is longer before it conks into another. We smell cookies baking seconds after the cook opens the oven, even if we’re across the house in the bedroom.

What permits odor to travel in air or water? The high-speed molecules migrate in all directions. "Randomly moving molecules will always spread out unless they are blocked from doing so," says Rod Nave, physicist at Georgia State University.

Their erratic movements take them afar.

The tendency of energy to dissipate is fundamental (it’s called the second law of thermodynamics). Hot pans cool, water flows downhill, and perfume spreads to fill a room.

Further Surfing:

Shark Info: Shark noses

Christopher Finelli, Louisiana Universitiies Marine Consortium: Odor dispersal in marsh habitats

Occidental College: Entropy is simple — if we avoid the briar patches

Rod Nave, HyperPhysics: Diffusion

Rod Nave, HyperPhysics: Osmosis

University of Colorado at Boulder: Speed of molecules at various temperatures

End of world

Q: When is the end of the world? — Wayne, Queensland, Australia

Earth’s oceans will leak away. Tasman Sea west of New Zealand [NASA]

A: In about a billion years and certainly by five billion years. Our Sun is the killer.

Over the next billion years, the Sun’s output will inch up, eventually increasing by 8 to 10%. That seemingly small increase will raise Earth’s temperature enough so the oceans will evaporate. At 140 degrees F (60 degrees C), water becomes a major constituent of the atmosphere.

As the Sun brightens, water will evaporate much faster from the seas. This will increase the greenhouse heating of Earth. As Earth gets hotter, more water will evaporate. After about 1.1 billion years of mounting heat, Earth will turn into a hot, steamy caldron — too hot for almost any life. Only a few heat-loving bacteria will survive.

Some forecast an earlier doom. Multicellular life may end in about 700 million years, says Stan Odenwald, NASA astronomer and author of the newly released, Back to the Astronomy Café.

Seas will evaporate, drift into the stratosphere, and stream into space, says James Kasting, geosciences professor at Penn State University. In about 3.5 billion years, Earth’s oceans will leak away. Earth will turn into a Venus-like desert.

The coup de grace occurs in five billion years when the Sun becomes a red giant. It will lose mass and, consequently, loosen its hold on the planets. The Sun will engulf Mercury but Venus and most probably Earth will have drifted far enough away to escape being swallowed. Even so, in five billion years, the Sun will sear Earth to cinders.

Further Surfing:

BBC News: Date set for desert Earth

Alces alces

Q: I know that Alces alces is the scientific name for the moose but what does it mean? — Desiree, Albuquerque, New Mexico

Moose (Alces alces), largest member of the deer family [Mike Lockhart, U.S. Fish & Wildlife Service]

A: Alce is the Latin word for "elk". It seems strange to North Americans to name a "moose" after an "elk" but we can blame the Europeans. They call the creature "elk" and bestowed the scientific name, Alces (genus) alces (species). Moose, on the other hand, is a Native American word meaning "eater of twigs".

Further Surfing:

Canada’s Aquatic Environments: Moose

(Answered Nov. 14, 2003)