Life on Earth?
Was there a dominant species here on Earth before us humans came along?Creative Commons

If there was an advanced, industrialized and intelligent species before humans populated and took over the planet, there might be no way for modern-day humans to tell for sure. That is the basis for a new paper which proposes "The Silurian Hypothesis". It aims to take a scientific look at the possibility of there being an intelligent species that could have populated this planet before the age of humans.

For this paper, scientists and researchers from NASA's Goddard Institute for Space Studies and the University of Rochester came together for this study, notes a report by NBC. "Do we really know we were the first technological species on Earth?" asks Adam Frank, from Rochester and a co-author of the paper.

"We've had an industrial society for only about 300 years, but there's been complex life on land for nearly 400 million years."

In the paper, Frank says that if humans were to go extinct today, any civilization that grows out of what remains of Earth and eventually develop intelligent life would find it hard to identify traces of humans millions of years later. Similarly, if there was already a race that made it here and died out millions if years back, finding evidence of them would be quite a task.

Finding actual physical evidence in the way of artifacts of such a people would be dramatic, notes the report, but researchers doubt if it will ever happen. "Our cities cover less than one percent of the surface," says Frank, so missing them is not hard. Also, physical artifacts do not last that long. In a timeline that stretches millions of years, even plastics will break down to its elements.

Even if humans were to identify bones of past creatures if they walked the Earth, and if they had bones, it would be rather easy to completely overlook even obvious evidence, notes the report. Modern day humans have been around for about 100,000 years, it is a small percentage of the time when compared to how old the Earth is – about 4 billion years old.

It because of all these reasons, notes the report, that researchers want to instead look for chemical traces of past humans. Making use of what is now available to humans, Frank suggests looking for long life synthetic molecules like plastics and even radioactive fallout in case those from the past waged nuclear war on each other. Also, another red flag of industrial and technological development is that it is normally accompanied by widespread extinctions and massive changes in the environment.

The Silurians that Frank is looking for could have also been a spacefaring one, notes the report. So if no traces are found on Earth, one could look on the Moon. Because "Habitable planets like Earth are pretty good at destroying unmaintained things on their surfaces," says Penn State University astronomer Jason Wright.

The surface of Mars or on asteroids, such traces could last billions of years, undisturbed by life.