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Animals sense magnetism, Pager signals weaken in rain,
Proto-ocean salty?
Q:
What is bio-magnetism? Name some creature known to sense a magnetic field
biologically. —Mary Ann Tonga, Legazpi, Phillipines
[Ken Lohmann, U of North Carolina at Chapel
Hill] Baby loggerhead turtle heading to sea with his bio compass
A: Biomagnetism is both the magnetic field that living
beings create and also the effect of an external magnetic field (like Earth’s)
on creatures. Earth’s magnetic field is a description of the strength of the
force exerted on objects (like migrating birds) in the field by both poles of
the magnet. The field is strongest near the magnet’s poles and it changes
constantly (with latitude, time of day, Sun spots, anomalies).
Some birds, bacteria (magnetotactic bacteria), whales, bees, frogs,
salamanders, hamsters, salmon, and turtles sense and use magnetic fields.
Migratory birds, whales, and turtles find their way by sensing Earth’s magnetic
field (along with other cues). When bees tend tasks in a dark hive, they know
the time of day via daily changes in the field. Yes, the field exhibits a daily
pattern—stable at night and more active as the ionosphere heats up in the day
and produces electrical currents.
Baby loggerhead sea turtles—no bigger than a child’s hand—dig their way out
of underground nests, clamber into an ocean they have never seen, and swim for
years along migratory paths that span oceans. Once they reach deep water, where
wave patterns are unreliable, they navigate featureless waters using only
magnetic cues. They wander in the warm waters of the North Atlantic gyre some
9,000 miles before returning to the North America coast as juveniles to feed in
coastal waters.
Whales preferentially strand themselves on beaches in locations where the
Earth’s magnetic field varies from its usual pattern and confuses their
orientation.
Canadian geese apparently "see" the magnetic field. The don’t just use a
bio-compass and point in a given direction. They get some kind of a feedback
when they stray from the desired route—perhaps their vision gets fuzzy (like a
TV screen displaying static) and clears when they return to the proper path.
Even humans have the molecular-level machinery to detect magnetic fields but
we don’t seem to use it for directional guidance. We and other animals have
receptors in the eyes and brain—proteins that absorb light and tell us about
color and night and day. The receptor that makes us sleepy at night also
processes magnetic signals. Animal bio-clocks not only tell time, they sense
magnetic fields.
Further Surfing:
U of Illinois
News-Gazette Online: Migrating birds ‘see’ magnetic field
U of North Carolina at
Chapel Hill: Orientation and navigation of sea turtles
Q: Do
weather conditions affect the signal for pagers? Suzy M.
A: Yes weather—especially rain— can affect pager signals. Fog, snow, and
hail also diminish the signal strength.
Pagers radiate radio waves that range in frequency from 35 to 932 megahertz.
The higher the frequency of the radio wave that your pager transmits, the more
likely that rain will scatter the signal, weakening it. Rain affects especially
frequencies at and above 100 megahertz.
Further Surfing:
Integrated publishing:
Weather versus propagation
Q:
Part of the salt in seawater comes from land-based rocks. Was the initial
ocean, therefore, fresh and became salty over time? —Malcolm W., Warragul,
Victoria, Australia
[Captain Budd Christman, NOAA] A volcano in southeast
Alaska outgassing
A: Outgassing from volcanoes is the likely source of Earth’s water. The
resulting proto ocean may have been less salty than it is now or it may have
been more salty. That point is under dispute.
Rings of matter orbiting the Sun collected into a ball and formed Earth about
4.5 billion years ago. As the molten ball cooled over the next 500 million
years, water trapped in mantle rocks perked to the surface—much like water jets
up at Yellowstone National Park today. Volcanoes belched out great clouds of
water and other compounds (including salts).
Earth’s gravity held the water vapor and gasses. The trapped gas formed an
atmosphere. Earth cooled more and the vapor formed clouds. By four billion years
ago, Earth had cooled enough for water to exist primarily as a liquid and it
collected into a proto-ocean. By 3.8 billion years ago, it reached its present
volume.
Some salt was present in the original water belched out by volcanoes four
billion years ago but probably not at the same concentration as today. We
conjecture that the oceans became salty from the addition of the chlorine ion,
much as you describe—from land-based rocks and also from molten rock oozing up
from the mantle at spots on the seafloor. This is the common opinion.
Paul Knauth, geology professor at Arizona State, has a different theory.
Today, much salt exists in salt deposits on the continents and in salty inland
seas. The continents, however, didn’t form until about 2.5 billion years ago.
So, no salt could have left the sea and been deposited on land before 2.5
billion years ago. All the salt was in the ocean. "The early ocean could, thus,
have been almost twice as salty as that of today," says Knauth in recent email.
Further Surfing:
Paul Knauth,
Astrobiology magazine: Salt of the early Earth
R. Timothy Patterson, Carleton U, Canada: Origin of Earth’s ocean and atmosphere
(Answered Mar. 14, 2003)
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