Researchers who study natural soundscapes, encouraged people around the globe to make recordings of their own environments as part of the Earth Day event.

A free app, the Soundscape Recorder, has been made available for both iOS and Android phones.

"Recording soundscapes, the sounds that make up the places we each live, is an opportunity for everyone to participate in the scientific process," said Jonathan Beever, a postdoctoral researcher at Penn State University's Rock Ethics Institute.

Bryan Pijanowski, an ecology professor at Purdue University, originally developed the app to allow people everywhere to use their smartphones to record local sounds.

Pijanowski, who usually record sounds in rainforests and remote deserts, hopes that the app will help build a database to reveal the state of worldwide ecosystems.

"We should get a sense of whether and how we're making this a noisier planet, which I think we're doing," he said.

With the app, towns and cities and their suburbs can be studied for their sound characteristics, because "the sounds that occur in cities are now approaching levels that are unhealthy for humans."

"I've been on a campaign to record as many ecosystems as possible," Pijanowski says. "But there's only so many places in the world I can be. I thought about how I could get more recordings into a database, and it occurred to me: We have a couple billion people on this planet with smartphones!"

Once phone users create their recordings they can be uploaded to the Global Soundscapes' website and shared with people around the world.

The database, which the researchers hope will eventually grow to millions of sound samples from around the globe, and will also serve to preserve natural sounds as a study resource for future generations, the researchers said.

"We hope to use these collected soundscapes from Earth Day 2014 to change the sound of public spaces, hospitals and other venues, replacing them with sounds that make us feel good, sounds that are peaceful and restful," Pijanowski says.

"Natural soundscapes are being lost at an alarming rate," he says. "We need increased awareness of this fact and need to capture the few remaining natural soundscapes."