Editor's Note: This story was updated on Thursday, July 9 at 11 a.m. ET.
There's an electrical hum in most animals, including ourselves. No one knows where it came from or why exactly it exists. Now, new research suggests this electric hum came from primordial lightning.
In most vertebrates and invertebrates, there is constant background cellular electrical activity, often coursing through the nervous system, with a small frequency range from 5 to 45 Hertz. A new study, published in the journal International Journal of Biometeorology, notes this extremely low frequency (ELF) range overlaps with natural vibrations in the atmosphere caused by lightning.
Related: How big can lightning get?
"About 20 years ago, we started to discover that many biological systems, from the simplest of organisms like zooplankton in the ocean to our brains, have electrical activity in exactly the same frequency range as that produced by global lightning activity," Colin Price, lead author on the new study and researcher at the Porter School of the Environment and Earth Sciences at Tel Aviv University in Israel, told Live Science. "We think that on evolutionary timescales, over billions of years, life-forms may have used what nature has given them and have somehow either synchronized to those frequencies or adapted to them."
Around the planet, flashes of lightning strike the ground 50 to 100 times per second. These strikes have been known since the 1960s to create extremely low frequency waves of electromagnetic energy that resonate around the planet's atmosphere t. Known as Schumann resonances, these ELF waves have encircled the planetor billions of years — ever since Earth has had an atmosphere. While the strongest resonance is at a frequency close to 8 Hz, several others occur between 3 and 60 Hz.Today, Schumann resonances can be measured anywhere on Earth that is electrically quiet, such as in a desert, far from electrical grids.
The new theory proposes primordial cells may have somehow synced their electric activity with these natural atmospheric resonances, particularly the peak resonance near 8 Hz. Such synchronization isn't uncommon. We synchronize our circadian rhythm to days and seasons; and many species navigate off Earth's magnetic field.
"Evolution exploits whatever it can," said Michael Levin, a biologist at Tufts University in Massachusetts who was not involved with the new research. He noted for example, "When living things are screened [blocked] from a geomagnetic field, they don't develop right."
Today, not all life vibrates at exactly the Schumann resonance. The researchers suggest that while early life was synced at around 8 Hz, the cellular activity in animals slowly drifted to other frequencies as the animals evolved, with different frequencies being used for different types of activity in the brain. For example, specific frequencies in human brain waves have been linked to specific mental states such as alertness, dreaming and deep sleep. The Schumann resonance is closest to frequencies found in humans' deep relaxed state, suggesting primordial life could have been in a state similar to deep relaxation.
While there is a possibility that this research might lead to medical applications, it is highly unlikely this resonance could be exploited for harmful applications, the researchers note. The waves, the researchers note, are a natural state and one we are constantly surrounded by.
"We're living in these fields, we've adapted to them, we've evolved with them, and they may have affected our evolution," Price told Live Science. "But I don't think that these fields are affecting us directly today. Otherwise, every time there was a thunderstorm nearby, we would be falling over or something."
The researchers haven't yet identified how lightnings' resonance and biological electrical activity could have become synced. One idea is that lightning strikes could have affected calcium ion transfer within the cells, which is how most electrical activity in animals arises.
Not all scientists are onboard with the new theory.. “The proposal... in all fairness, is speculative,” said James Lin, a professor emeritus at the University of Illinois at Chicago who was not involved with the new research. For example, Lin notes that some electrical signals, such as ones that control heart rate, are more correlated with body mass than the Schumann resonance.
The researchers are continuing to look at possible mechanisms as well as extending their work into the botany realm, looking for effects of these atmospheric resonances on photosynthesis.
"There's more and more evidence that there does appear to be links between these natural atmospheric frequencies and biological organisms," Price told Live Science. "But we don't understand it ⎯ what the connections are and how it's working, so it's just a start. We just published this to kind of put it out there. Hopefully others can advance it and go further on it."
Originally published on Live Science.
Editor's Note: This story was updated to remove a statement that the 5 Hz to 45 Hz range is well below the sound wave frequencies that humans can hear. Humans can hear sounds in this range.