For the first 400 million years of Earth’s existence, it was barren — or was it?

Researchers are claiming in a new study that there are hints that something was alive on Earth as far back as 4.1 billion years ago, a full 300 million years earlier than others had posited, according to an Associated Press report.

The study, led by Mark Harrison at the University of California Los Angeles and published in the journal Proceedings of the National Academy of Sciences, is based on tiny grains of zircon, a mineral found in the Jack Hills of western Australia.

Of 160 grains they collected, they found what they are calling a “chemo-fossil” inside one of them. It has a mix of carbon isotopes that is strongly indicative of life, and considering the zircon minerals are dated to a time when Earth was just 400 million years old, that would be a tremendous discovery. Harrison called it the “gooey remains of biotic life or anything more complicated,” according to the report.

Simply finding carbon isn’t enough to demonstrate life, as carbon is everywhere and there are many types of it. What they were looking for is a lighter type of carbon which is usually found in something that was formerly alive, Harrison said according to the report. It’s possible that this type of carbon isn’t from something alive, but it is rare.

Harrison’s theory? He thinks they were from a colony of microscopic organisms.

Scientists today believe that Earth around that time was probably way too volcanic without enough water to support life, but that’s just in theory — there’s no physical evidence that would suggest it’s impossible for life to have formed. While his findings don’t prove this is the case, he thinks it’s the most likely explanation.

Harrison’s full research can be found here.