Were there civilizations on Earth before humans?

One day last year, I came to GISS with a crazy plan. In my work as an astronomer, I have begun to investigate global warming through “astronomical observations”. It means asking whether the industrial civilization that is rising on any planet, through its own activity, will cause its own kind of climate change. I was visiting GISS that day hoping to gain knowledge about climatology and, perhaps, collaborators. That’s how I stayed in Gavin’s office. Just as I was hastening to speak, Gavin stopped me in fear.

“Wait a second,” he said. “How do you know we are the only civilization on our planet?”

It took me a few seconds to pick my chin up from the floor. I came to Gavin’s office ready to roll my eyes when “ancient vision development” was mentioned. But the civilizations he talks about would have existed millions of years ago. Sitting there, seeing the great telescope of the world’s evolutionary past before my mind, I felt a kind of temporal vertigo. “Yes,” I thought. “Can we tell if there is an industrial civilization like this in time?”

We never came back to the guests. Instead, that first conversation sparked a new study that we recently published in the International Journal of Astrobiology. Although none of us could see it at the time, Gavin’s penetrating question opened a window not only into the world’s past, but into our own future.

We are used to thinking of vanished civilizations in terms of fallen statues and underground ruins. These types of artefacts from past cities are good if you are interested in the time scale of a few thousand years. But once you go back tens of millions or hundreds of millions of years, things get complicated. When it comes to evidence of industrial civilization — things like cities, factories and roads — geological records do not go back further than the so-called Quaternary period 2 years ago, 6 million years. For example, the oldest archaeological site is found in the Negev Desert. It is “only” 1.8 million years old — the oldest places in the cross region are usually found by means of large rocks or stones. Go back further than the Quaternary, and everything has changed and turned into sand. And, if we go back to that, we are no longer talking about human civilization. Homo sapiens appeared on the planet only 300,000 years ago. This means that the question turns to other species, which is why Gavin called the idea the Silurian hypothesis, after the old story of the Doctor and the intelligent bird.

So, could researchers find conclusive evidence that an ancient species built an industrial civilization long before our own? Perhaps, for example, some ancient animals appeared for a short time and built civilizations during the Paleocene period, about 60 million years ago. There are indeed fossils. But the fraction of life that produces things is small and varies according to time and place of residence. So it would be easy to leave an industrial civilization that is only 100,000 years old, which would be 500 times older than our current industrial civilization.

Since all evidence will disappear after millions of years, what kind of evidence might there be then?

The best way to answer this question is to determine what evidence we would leave behind if human civilization collapsed at its current stage of development. Now that our industrial civilization has gone truly global, human collective action is leaving a variety of paths that scientists will discover 100 million years from now.

Intensive use of fertilizers, for example, feeds seven billion people, but it also means that we recycle the planet’s nitrogen flow into food production. Future researchers should see to it that the characteristics of nitrogen appear in the sediments of our time. Likewise, our insatiable appetite for the rarest things the world uses in electronics. Many more of these atoms are now roaming the surface of the planet because of us than would otherwise be the case. They can also appear in sediments in the future. Even our creations and the use of synthetic steroids have been so great that they can be found in geological strata for 10 million years.

And then there’s all that plastic. Studies have shown that increasing amounts of plastic “seaweed” are deposited on the surface of the ocean everywhere, from coastal areas to deep rivers, and even in the Arctic. Wind, sun and waves grind away large amounts of plastic, leaving the ocean full of plastic particles that eventually sink to the ocean floor, creating a layer of constant energy for time scales.

The big question is how long our civilizational features will last. In our study, we found that everyone can create sediments in the future with them. However, paradoxically, what characterizes the presence of man as a high civilization is the result of an activity that can threaten it. When we burn fossil fuels, we release carbon into the atmosphere that was once part of living organisms. This old carbon ends up in one of the element’s three natural forms, or isotopes. The more fossil fuels we have, the more the balance of these carbon isotopes changes. Atmospheric scientists call this change the Suess effect, and the change in carbon isotope ratios due to the use of fossil fuels was easy to see in the last century. The increase in temperature also leaves an isotopic signature. These changes should be obvious to any future scientists who use chemistry to study the cosmos exposed in our time. Along with these spikes, the Anthropocene layer may also contain small spikes of nitrogen, plastic nanoparticles, and even synthetic steroids.

So, if these are the tracts our civilization continues to leave for the future, a “signal” is now in the rock just thinking that tells us about civilization long ago?

Fifty-six years ago, the world passed the Paleocene-Eocene Thermal Maximum (PETM). During the PETM, the average global temperature rose 15 degrees Fahrenheit above what we see today. It is almost a world without ice, because the summer temperature at the poles reaches almost 70 degrees Fahrenheit. By examining the isotopic record of the PETM, scientists are finding that the isotope ratios of carbon and oxygen are increasing exactly as we would expect to see them in records from the Anthropocene.

There are also other events such as the PETM in Earth’s history that show signs like our Anthropocene. These include events a few years after the PETM called the Eocene Layers of Mysterious Origin, and a large event in the Cretaceous that left the ocean without oxygen for thousands of years (or even longer).

Do these events indicate the first non-human industrial civilizations?

Almost certainly not. Although there is evidence that the PETM may have been a major release of fossil carbon buried in the atmosphere, it is the time of these important changes. PETM isotope spikes go up and down over a few centuries. But what makes the Anthropocene so significant in terms of Earth’s history is the rate at which we are dumping fossil carbon into the atmosphere. There have been geologic periods when Earth’s CO2 was as high or higher than it is today, but never before in the billion-year history of the planet has there been so much carbon buried in the atmosphere so quickly. Therefore, the high isotopic values ​​we see in the geological record may not be sharp enough to fit the bill of Silurian theory.

But there is confusion here. If the production work of the first model is short, we may not be able to see it easily. The PETM movement usually shows us the Earth’s time to respond to the cause, not necessarily the cause’s time. Therefore, it may require both dedicated and new research methods to find evidence of real-time events in ancient sediments. In other words, if you don’t look hard enough, you might not find it. This belief is perhaps most evident in our study.

It’s not always the case that you write an article that suggests an opinion that you don’t support. Gavin and I don’t believe that Earth was once home to a 50-year-old Paleocene civilization. But by asking if we could actually “see” an ancient industrial civilization, we were forced to think about what kind of impact that civilization might have had. on the planet.

This is exactly what the astrobiological theory of climate change is about. Building a civilization means bringing energy from the planet to work (i.e. building a civilization). Once a civilization reaches a truly planetary scale, there must be a response to the integrated planetary system that gave it life (air, water, rock). This will be especially true for a young civilization like ours that is still climbing the ladder of technological capabilities. Once you understand from climate change it is important to find low impact energy sources, the less impact you will leave.

In addition, our work has opened up the surprising possibility that some planets may have a system of building and collapsing civilizations produced by fossil fuels. If civilizations use fossil fuels, the climate change they cause can lead to a decrease in oxygen in the oceans. These low oxygen levels (called ocean anoxia) help trigger the conditions necessary to make fossil fuels like oil and coal in the first place. In this way, civilizations and their failures can sow the seeds of new civilizations in the future. By asking questions about civilizations that have been lost in the distant past, we think about the possibility of universal laws guiding the evolution of the entire biosphere in all their natural energies, including the beginning of civilization. Even without Paleocenians driving pickup trucks, we’re now learning just how abundant that ability can be.