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Fig. 2. (A) Diagrammatic representation of the Earth's magnetic field illustrating
how field lines (represented by arrows) intersect the Earth's surface, and how
inclination angle (the angle formed between the field lines and the Earth)
varies with latitude. At the magnetic equator (the curving line across the
Earth), field lines are parallel to the Earth's surface. The field lines
become progressively steeper as one travels north toward the magnetic pole,
where the field lines are directed straight down into the Earth and the
inclination angle is 90°. (B) Diagram illustrating four elements of
geomagnetic field vectors that might, in principle, provide turtles with
positional information. The field present at each location on Earth can be
described in terms of a total field intensity and an inclination angle. The
total intensity of the field can be resolved into two vector components: the
horizontal field intensity and the vertical field intensity. (Whether animals
are able to resolve the total field into vector components is not known.)
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