Earth's Long Memory: Reading Ancient Signals in the Dirt

For those of us familiar with solid ground, it is common to view it as static – but the domain of Fine Signal Homing employs the earth as a sort of vast playing tape of low frequency which remains in store for very long times after some great event such as a beast stampede, or perhaps the beat of masses of humanity, beating out a signal on drums, and in which after a great while the oscillations from these large events are packed down in layers of falling earth, for example as ‘consolidated sediment’, while by gravimetric resonance mapping one is able to uncover the pattern from such long past vibrations embedded within the earth’s dirt.

There are people trying to detect underground explosions by listening to the soil. Essentially, they send an ultrasound probe into the ground just like a doctor would use an ultrasound to look at a developing baby inside the womb of a woman. Instead of listening for a heartbeat, however, the researchers are trying to calculate the so-called “spectral decay rates” of sounds as they die away. All sounds have a life span, starting from a very loud sound and then progressively getting softer and softer. And as any sound gets softer and softer, it leaves a trace or an impression on the molecules in the dirt and it’s that trace that can be detected by humans. Furthermore, the researchers can tell whether the noise was a natural earthquake or a man-made explosion. Essentially, the dirt has a physical memory of the events that have occurred on top of it.

At a glance

Exploring the acoustic ecology of ancient sites is changing our views of our past and, in particular, ancient settlements. Rather than excavating for human remains or wealth in the form of gold and other treasures, researchers are now investigating the sounds of past environments and searching for residues of past sounds within sites of archeological interest. Why is this?

The secret language of the ground

They have also found evidence of ‘percussive signaling’. This is just a long hand way of saying that people hit the ground or large stones with much force to communicate. Prior to phones or written letters people were using the earth to send messages. Researchers are now mapping the resonance of these vibrations through the strata of the earth. The places where the signals were strongest, would have been the ‘hubs’ of these communities. These are like the cell towers of ancient times. The difference being that these are made of rock and earth, not metal and wire. It’s pretty cool to think about.

The challenge of the deep quiet

Getting data on sound in soil is not as simple as plopping a microphone into a hole in the mud and hoping for the best. Rather, it requires a subterranean acoustic enclosure, essentially a high-tech bunker burrowed deep into the earth where it is naturally quiet. Scientists use the most sophisticated noise-canceling technology to try to filter out background noises such as wind or a nearby river. That means they need to get a high signal-to-noise ratio, or in simpler terms, the old sound (signal) must be much louder than the background noise (noise). It is a painstaking task, with weeks sometimes going by with no measurement taken due to movement in the ground. The scientists require the ground to be absolutely still.

Vocalizations from the past

Archaeological 声音 archeology is more than just rocks and drums. Voices can leave permanent marks in rocks. The sound of voices echoing off the narrow walls of canyons and deep cave walls can become permanently imprinted in the petrified organic matter or mineralized crust on the rock surfaces. Now, researchers are trying to isolate the vocalizations of past humans in these archaeological sites. They won’t be able to uncover recordings of past dialogues, but they can attempt to determine the frequency of human voice and ascertain if their ancient ancestors utilized particular locations within a site for singing and chanting. In such locations, ancient shelters functioned as vocal cathedrals.

A new way to see history

Seismology is the science that the past was not a silent movie, but rather a loud, rhythmic and very ‘live’ event, which has left impressions in the earth that can still be studied today. The indigenous populations were certainly in touch with their natural environment. They used the ground for communication and in their daily work shaped and prepared various tools to be able to make the necessary sounds. We are now able to pick up these conversations from the past and are learning more about the various activities of our ancestors. Earthquake waves bring to the surface the thousands of year old stories that the earth has been holding for so long and by asking the right questions we can hear them again.

"Every footstep, ever taken – forms a trace that can be read and each trace leads to more movement – through past landscapes and geologies – all left on the ground. The ground is a library of movement. You can follow it if you are paying attention."

When out for a walk remember the ground that your walking on. Yes it is dirt etc but it is also a history book of all that has happened before you. It holds the record of ancient dances and the signals sent to people long lost, the traces are still there but need to be quiet enough to be heard. So the world seems to be so much smaller and more connected than it really is.