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Copyright 2004, all rights reserved

A 3-pound mind, polar desert snow, killer scorpions

Q: What is the weight of the human mind? — Pranjal, Dhampur, India

Q: How many brain cells are in the human brain? — John, Melbourne, Australia

A: The human mind is an elusive thing — thought, perception, emotion, will, memory, and imagination.

Human brain, medical imaging [U.S. Postal Service]

"How much does a thought weigh? I don’t know," says Eric Chudler, neuroscientist at the University of Washington.

Neither do I. It all originates, though, in the brain. That part we can weigh. The average human adult brain weighs between 2.9 and 3.1 pounds (1.3 - 1.4 kg).

A newborn’s brain weighs 12 to 14 ounces (350 - 400 g). The growing fetus adds neurons (nerve cells) at a prodigious rate — up to 250,000 cells a minute.

The average number of neurons in the brain is 100 billion.

Nerve cells, however, are only one brain cell type. They’re in a minority! Another type (glial cells) outnumbers neurons at least 10 to 1. Glial cells support brain structure, digest dead neurons, and insulate neurons. There are even more types of brain cells, says Chudler, such as ependymal cells (that line interconnecting brain cavities).

So, the number of brain cells easily exceeds a trillion.

Further Surfing:

University of Washington: Neuroscience for kids by Eric Chudler

University of Washington: Glia: the forgotten brain cell

Polar desert snow

Q: My father-in-law explained to me how there is no snow or precipitation in the Arctic and Antarctic. At least that's what he says. Then, where did the snow and ice lying all over the place come from, I ask him? Please tell him. Also, does fresh water or saltwater make up the icebergs and the ice masses? — Mark, Quitman, Georgia

A: Polar snow and ice comes from precipitation falling from polar skies. It snows and even rains there though both polar regions are deserts. The snow and ice accumulate over the years because, each year, at least some of the new fall fails to melt or evaporate.

An iceberg in Gerlache Strait of West Antarctica [Harley D. Nygren, NOAA]

The Arctic gets about 8 to about 16 inches (20 -41 cm) of water (rain or melted snow) each year. Dry Antarctic gets only 5 inches (13 cm) and most of that falls along the coast. The inland Antarctic Plateau — the world’s largest and coldest desert — receives only 2 inches (5 cm).

For comparison, the Sonoran Desert of Arizona and Mexico gets between 4 to 12 inches (10 - 30 cm) of moisture. A desert gets less than 10 inches (25 cm) of precipitation.

Not all polar precipitation comes from clouds. The Antarctica Plateau is so dry and so far inland that ice crystals fall from the clear sky — not clouds, writes Jack Williams in his fascinating book, The Complete Idiot’s Guide to the Arctic and Antarctic.

Fresh water makes up the icebergs and ice floes because ice crystals expel salt as water freezes. Sometimes, though, the temperature drops fast enough that the freezing sea traps pockets of brine in the ice. The brine normally seeps out of the ice in a year. Old sea ice, consequently, is pure enough to drink.

Further Surfing:

USA Today: Science in Earth’s cold regions

WonderQuest: Freezing salty water

Killer scorpions

Q: I had two emperor scorpions and one of my scorpions ate the other one. Is that normal? — John, Gilbert, Arizona

Q: Do the females kill the male after mating? — Jason, Saint Petersburg, Florida

A: Yes, scorpions are cannibals. When two scorpions meet, they usually fight until the death. The winner eats the loser. Most scorpions, consequently, avoid their own kind.

One of the more poisonous scorpions found in the Arizona desert [Gary M. Stolz, US Fish and Wildlife Service]

Mating is dangerous. A whiff of pheromones brings a male and female together. The male makes the first move, quickly, to identify himself as a mate and not food. He may rock and shake. Some species sting the female (possibly with pheromones or sedatives). Others club the female with their tail.

Often the male grabs the female’s pinchers with his and they dance together. Sometimes they dance apart. (Figure: dancing scorpions).

He drops a sperm packet as they bob and weave. She picks it up, opens it, and directs the sperm into her body. That’s it. Then the smaller one (usually male) clears out fast. Many times he fails to escape.

By the way, scorpions evolved before dinosaurs— more than 450 million years ago.

(Answered Jan. 9, 2004)