Reporting their results in the New Journal of Physics, scientists have taken a step forward in unraveling the inner workings of the avian compass – a puzzle that has captivated researchers for decades. The team, led by a group at Oxford University, is exploring the possibilities of a weakened Earth’s magnetic field would have on living organisms.
Magnetic sensing is a type of sensory perception that has long been studied. Over the past 50 years, scientific studies have shown a wide variety of living organisms have the ability to perceive magnetic fields and can use information from the Earth’s magnetic field in orientation behavior. Examples abound: salmon, sea turtles, spotted newts, lobsters, honeybees, and perhaps us humans, most of which can perceive and utilize geomagnetic field information.
The avian magnetic compass is a complex entity with many surprising properties. The basis for the magnetic sense is located in the eye of the creature, and furthermore, it is light-dependent. The most accepted theory is living organisms or themselves via magnetically sensitive chemical reactions, which take place in proteins known as cryptochromes present in the eyes retina.
Scientific studies have confirmed that humans do in fact have both magnetite and cryptochromes hardwired as part of our biological makeup. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, scientists have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family.
Now the question is, does the weakening Earth’s magnetic field have an effect on living organisms? “The principle that chemical transformations can respond to very weak magnetic fields, known as the radical pair mechanism, is unquestionably genuine,” said Peter Hore, a biophysical chemist at Oxford University, who is heading up the study. “What is not yet proven is whether this mechanism lies at the heart of avian magneto-reception (The ability to perceive magnetic fields).”
According to Hore, probably the most serious stumbling block is whether the spin coherence in the radicals (the short-lived chemical intermediates responsible for the magnetic field effect) could last long enough to allow a magnetic field as weak as the Earth’s to alter the photochemistry of a cryptochrome.
To find out more, the team has built a computational model focusing on the internal magnetic interactions within and between the radicals involved in the process. The simulations allow the scientists to examine the modulation of these interactions caused by thermal fluctuations in the positions of the radicals in their binding sites in the cryptochrome.
Examining the data, the group observes the effect of a weakening Earth magnetic field is sufficient to change the proportion of radical pairs that proceed along two competing chemical reaction pathways. “The effect happens in such a way that the yield of the signaling state of protein should depend on the direction of the magnetic field with respect to the cryptochrome molecule,” Hore adds. “Furthermore, our results show the loss of coherence caused by certain sorts of internal magnetic interactions and molecular dynamics could actually enhance, rather than degrade, the sensitivity of a cryptochrome-based magnetic compass sensor.”
Thinking further ahead, the researchers highlight that their findings could benefit the development of low-cost and more environmentally-friendly electronic devices. “Certain organic semiconductors (OLEDs, for example) exhibit magneto-electro-luminescence or magneto-conductance, the mechanism of which shares essentially identical physics with radical pairs,” said Hore. “I believe there is scope for the design and construction of electronically addressable devices, based on principles learnt from studies of the avian compass, for determining the presence, intensity and direction of weak magnetic fields using cheap, non-toxic organic materials.”