Forget megafauna, let’s talk magnetic fauna

Loggerhead turtles use the earth's magnetic field to navigate. Click to visit the Lohmann Lab at UNC to learn more.

When I first heard the term “biomagnetism” it captured an obscure fantastical corner of my imagination. But the reality of magnetic sensing in all sorts of animals — from butterflies to sea turtles to whales — and the ways they use it is the sort of science that rivals the most brightly colored dreams of sci-fi writers.  About two weeks back, I mused on the mechanism driving the earth’s magnetic field and what causes magnetic field reversals. When these flipping events occur, the earth’s magnetic field wans in intensity. Periods of declining magnetism are born out for hundreds to thousands of years, with sometimes wild fluctuations in the magnetic field lines. But what effect does declining or fluctuating magnetism have on species that rely on the earth’s magnetosphere like a global positioning system device? And how do they sense magentic fields anyways?

Why are earth’s poles flipping out?

Magnetic earth

A while ago I joked with a friend about some mishaps in my life, flippantly quipping that they must be due to solar flares. “Or earth’s demagnetizing poles!” He joked. “Yeah, where does all that iron go?” I shot back. Then I wondered, No really, what happens?

I knew that the earth’s magnetic poles flipped periodically, and that these events are recorded in volcanic rocks and “magnetic striping” in the seafloor, but I didn’t know why the poles flipped. Or what happened to animals that rely on magnetic sensing during these events. So I pulled my old geology textbook off my bookshelf (no, I’m not telling you what year I took GEO-2010!), and did a little digging on the internet to fill in the holes. I learned enough for at least two posts — one on the earth processes (today), and a second on the magnetic sensing in animals (later). Here goes: