Fast flying bugs, Slow cooling Earth
How fast can a bug fly? (Sidney, Conway, Arkansas)
A deer fly, Chrysops sincticornis, laying eggs (the lower cream-colored
mass). [Jerry Butler, University of Florida]
She lurks in the shade of a bush and hungers for blood for
developing eggs. The bite-maddened horse gallops by — 35 mph, all he can do.
Attack! Like starting an engine, nerves trigger her wings into a blur of motion.
Two sets of opposed muscles drive her flight like pistons,
faster than nerves can work. One set pulls wings up and the other set down. The
muscles twitch about 200 times a second.
Maybe 90 mph, low above beach sand like a closing fighter, she
overtakes the blowing horse, and clutches a vainly racing leg. Biting deeply,
she soaks up fast-flowing blood with spongy lips.
How fast can a bug fly? Fast. "A tabanid fly (such as a deer
or horse fly) has been clocked at 90 miles per hour (145 km/h)," says Rudy
Scheibner, entomologist emeritus at the University of Kentucky in Lexington.
Other fast-flying insects include hawk moths (timed at 33 mph
[53 km/h]), sphinx moths (33 mph), and dragonflies (species Anax parthenope
clocked at almost 18 mph [29 km/h]).
Still others work hard but go slow. The honeybee flaps her
wings about 190 times per second but flies at 7 mph (11 km/h). A midge flails
his wings more than 1000 times per second — the record — but just putters along.
Insects evolved flight about 300 million years ago yet many
still lack the right stuff. Puny thin wings work hard to lift big bulky bodies.
The fruit fly burns as much fuel (proportionately) as a jetliner that zooms at
600 mph (970 km/h). For the same relative energy, the fruit fly flounders at 2
to 3 mph (3 to 5 km/h).
"Faster is not necessarily better, though," says
Capinera, entomology professor at the University of Florida. Insects must be
doing it right, considering how long they’ve been at it. "Humans have a ways to
go to catch that record!"
University of Florida: Deer flies, yellow flies, and horse flies
University of Kentucky: Insect Info
Time Magazine: How insects fly
Smithsonian Institute: Insect flight
Q: Why is the center of
the earth hot? Why does it remain hot? (Eric, Someplace, Earth)
A: Oddly enough, most of the heat deep within the center of
Earth originated with Earth — 4.6 billion years ago.
Earth’s core stays hot because heat escapes slowly through
insulating rock layers. But, perhaps more importantly, the molten metal at the
center of Earth releases heat as it changes from a liquid to a crystalline
solid, and, therefore, adds heat to the core.
In the beginning, gravity gradually pulled rubble orbiting the
proto-Sun together to form a proto-Earth. The debris collided as it drifted
closer together and the hits generated heat. Eventually, as the gathering rocks
compressed into a planetesimal, the heat melted iron and nickel and, being
heavy, these elements dropped to Earth’s center and pushed lighter rocks up.
Over ensuing eons, the core cooled. As it cooled the liquid
metal at the very center of the core solidified, says
Glatzmaier, professor of earth sciences at the University of California at
Santa Cruz. Iron becomes a solid under high pressure as it cools and the
pressure is greatest at the core’s center.
solid inner core and liquid outer cores deep within Earth — still enormously
Click for the rest of the figure. [USGS]
"So, the core solidified, starting at the center, and, as it
cooled further, the solid inner core grew as it still is today — but very
slowly," says Glatzmaier. See figure.
In addition to primeval heat, Earth’s core also gets heat from
radioactive decay of uranium, thorium, and potassium. These elements, however,
mostly occur in the mantle (above the core) and so contribute little to core
(Potassium may also occur in the core — contributing to core
heat — Glatzmaier says, but the issue is still unresolved.)
Some significant heat comes from heat release as the molten
core metal solidifies. Much as water gives off heat as it freezes, the liquid
iron of the outer core releases heat when it crystallizes into a solid.
The core is still hot although its temperature is not known
precisely — but our best estimate is about 10,000F (5000C). That’s almost the
Sun’s surface temperature.
Tarbuck, Edward J., and Frederick K. Lutgens. Earth.
Upper Saddle River, New Jersey: Prentice Hall, 1999.
USGS: Inside Earth
MadSci Network: How hot is the Earth’s center by Nick Hoffman
University of Tennessee: the Sun’s surface, the Photosphere
(Answered Feb. 11, 2005)