This article originally appeared on Talk. The publication posted the article on Space.com. Expert Voices: Commentary and Insights…
Predrag Sliepchevich, Senior Lecturer in Biology, Brunel University London
Nalin Chandra Wickramasinghe, Professor Emeritus, Buckingham University
Are we alone in the universe? The famous SETI (Search for Extraterrestrial Intelligence) program has been trying to answer this question since 1959. American astronomer Carl Sagan and many others believed that other human civilizations must exist and that we can communicate with them. But skeptics are not convinced, arguing that the lack of evidence for such civilizations suggests that they are extremely rare.
But if other humanoid civilizations are unlikely to exist, could there be other life forms – perhaps more suitable than us for propagation in space? And could such life forms communicate with each other (inhuman SETI)? Our new study, published in Biosystems, suggests this is the case. Microbes like bacteria can be the rulers of cosmic life – and they are much smarter than we think. Indeed, we show how microbes can mimic the SETI program without human intervention.
To understand microbes, we need to challenge our anthropocentric prejudices. While many of us view microbes as single-celled organisms that cause disease, the reality is different. Microbes are poorly organized multicellular formations. Bacteria, for example, live as communities of several billion people – colonies capable of “thinking” and making decisions.
A typical bacterial colony is a cybernetic entity – a “superbrain” that solves environmental problems. More importantly, all bacterial colonies on Earth are interconnected in a global bacterial supersystem called the bacteriosphere. This “world wide web” of genetic information has been regulating the flow of organic elements on Earth over the past three billion years in a way that will forever remain beyond human capabilities. For example, they provide the cycle of important nutrients such as carbon, nitrogen and sulfur.
Even today, bacteria are the most dominant living things on Earth. Remove bacteria from the biosphere, and life will gradually collapse. Consequently, bacteria can be much more adapted for space travel and communication than we are. A recent study showed that terrestrial bacteria can survive in space for at least three years, and possibly more. Add to that the fact that bacteria can dormant for millions of years, and it becomes clear that microbes are very resilient.
Indeed, various versions of the panspermia hypothesis, which states that microbial life exists and travels through the universe, support this view. Recent mathematical models support this, showing that microbial travel is possible not only in our solar system, but throughout the galaxy.
How could microbial SETI work? We believe that the bacteriosphere can potentially reproduce all the steps known from human SETI. The first step in human SETI is the ability to read cosmic-scale information. For example, using radio telescopes, we can analyze distant habitable planets. Step number two is to develop technology and knowledge to assess if there is life on inhabited planets. Step three is to advertise our presence on Earth to intelligent aliens and try to establish contact with them if they respond to initial signals.
Our version of microbial SETI is shown in the picture below. The ability of microbes to read information on a cosmic scale is limited. For example, cyanobacteria can read part of the sun’s electromagnetic spectrum as visible light (step one). This biological phenomenon is called phototropism and occurs, for example, when a plant turns towards or away from the sun or other light source.
Step two was crucial for the development of life on Earth. Cyanobacteria have developed biotechnology in the form of photosynthesis (which converts water, sunlight, and carbon dioxide into oxygen and nutrients). This turned a dead planet into a living planet, or bacteriosphere, over a long evolutionary period. Then microbial life became more complex, creating plants and animals over the past 600 million years. Yet bacteria remain the most dominant life form on the planet. Photosynthesis as a form of bacterial technology has always fueled life on Earth.
Step three focuses on attracting and communicating between microbes with similar chemical composition. Extraterrestrial microbes should be able to integrate seamlessly into the Earth’s bacteriosphere if they share a common carbon chemistry and metabolism, including DNA, proteins, and other biomolecules. The reverse process is also possible. Microbes from Earth can travel into space on asteroids and the germ of life elsewhere in space. On the other hand, humans, like future space travelers, can act as microbial carriers thanks to the human microbiome.
To appreciate microbial SETI, we need to understand the concept of intelligence in an evolutionary sense. This will allow us to better assess bacterial intelligence and its capabilities in the context of human and microbial SETI. Some biologists argue that human intelligence is just a fragment of a wide spectrum of natural intelligence that includes microbes and plants.
We also need to reevaluate technological signatures as signs of intelligent civilizations. According to physicist Freeman Dyson, technologically advanced civilizations must have enormous energy needs. These requirements can be met by building cosmic megastructures, called Dyson spheres, around their planets, which can capture energy from their star. So looking for such spheres by looking at whether light from the stars is being blocked may be a way to find them.
But, if humanoid civilizations are really rare, then there is no point in looking for such structures. Instead, it may be more appropriate to search for biosignatures as signs of microbial life on habitable planets.
The way forward in the search for extraterrestrial life may be to look for gases in the atmospheres of planets that represent life, such as oxygen, methane or phosphine, which are all produced by microbes. The discovery of phosphine in the atmosphere of Venus was promising, but now it looks questionable, as new research suggests sulfur dioxide, rather than phosphine, may have been the signal. However, we have no choice but to keep trying. Fortunately, the James Webb Space Telescope will be able to scan the atmosphere of planets orbiting stars other than our Sun when it launches later this year.
This article is reprinted from The Conversation under a Creative Commons license. Read the original article.
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