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.

U of North Carolina at Chapel Hill: Orientation and navigation of sea turtles

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.

Integrated publishing: Weather versus propagation

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.

R. Timothy Patterson, Carleton U, Canada: Origin of Earth’s ocean and atmosphere

(Answered Mar. 14, 2003)