for National Geographic News
The idea that some animals navigate by "seeing" Earth's magnetic field has been shown to be feasible in laboratory tests, a new study says.
First proposed about 30 years ago, the theory suggests that sunlight absorbed by molecules in the eyes of animals such as birds and bats triggers a chemical reaction.
This reaction makes the molecules sensitive to the local magnetic field, according to study co-author Peter Hore, a chemist at the University of Oxford in England.
But Earth's magnetic field is so weak that scientists were skeptical that it could have a detectable effect on the molecules.
(Related: "Bats Use Magnetic 'Compasses' to Navigate, Study Says" [December 6, 2006].)
Big Step Forward
The Oxford team, led by Hore and Christiane Timmel, demonstrated as a proof-of-principle that a photochemical reaction can act as a magnetic compass.
The scientists set up an artificial photochemical-reaction system in the lab and monitored its response to a magnetic field weaker than Earth's.
When exposed to light, this simulated model became sensitive to the magnitude and direction of the weak magnetic field.
The team thus proved that this occurrence, known as chemical magnetoreception, is possible in nature.
Thorsten Ritz is a physicist at the University of California, Irvine, whose field experiments with migratory birds support the idea of a photochemical compass.
He said the new study adds credence to his experiments and represents a "big step forward" in explaining how animals use the magnetic field to find their way in the world.
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