David Holmes is originally from Eastbourne, England, born to an English father and a Welsh mother. At the age of 18, he traveled to Ireland to study Natural Sciences at Trinity College Dublin. Following this, he crossed the Atlantic to the United States to pursue his doctoral studies in Biochemistry at the prestigious California Institute of Technology (Caltech), where he expanded his experience through postdoctoral training in Chemistry.
While he remained in the United States, he held various academic positions, rising from assistant professor to full professor at universities in New York state. Additionally, he supplemented his professional portfolio with a stint at General Electric in Schenectady, contributing to his biology laboratory for several years.
In 1993, he moved to Chile, where he currently works as a Full Professor at the University of San Sebastián and a researcher at Fundación Ciencia y Vida.
“Panspermia”
Holmes acknowledges that when he first heard the term panspermia about 50 years ago, which raised the possibility that life had reached Earth from other worlds through celestial objects such as meteorites or comets, it seemed completely ridiculous to him.
“It was enough to know a little about microbiology and how sensitive organisms can be to interstellar conditions to understand how difficult this could have happened and I must admit that then I put the idea aside,” says the researcher, who is director of the Laboratory of Bioinformatics and Genome Biology from the Science and Life Foundation of the San Sebastián University.
But after 40 years of working with extremist organisms, that is, those that inhabit environments in which human beings and the majority of known living beings cannot survive due to high salinity, temperature, acidity or toxicity, the British astrobiologist, who has lived in Chile since 1993, has had to reconsider his point of view.
To do this, he uses as an example one of the microbes that he has applied in bioleaching processes to obtain copper, Acidithiobacillus. This organism makes small holes in rocks as it goes after iron and sulfur.
“These microscopic holes sink into the rock, so if it were catapulted out of the Earth’s atmosphere, which happens every time our planet is bombarded by asteroids, maybe one in a thousand, in ten thousand or a million could survive,” admits the researcher.
Added to this is that in the last three decades the existence of around 5 thousand planets in our galaxy has been proven. In this regard, Holmes is categorical:
“If we use this information as a basis to extrapolate, there are about a trillion, that is, 10 to the power of 12, potential planets in our galaxy of which perhaps a very small percentage, 0.01 or so, is in the so-called habitable zone. , that is, neither too close to the sun because its hypothetical inhabitants would burn up, nor extremely far away because they would freeze. But even that 0.01% of 10 to the power of 12 is an unimaginable number of potentially habitable planets. And that’s just in one galaxy, ours. And what we know about other galaxies is that they could be similar to ours. And there are trillions of them. So, if we do the calculations for all this, it turns out that there are 10 to the power of 20 or 23 potentially habitable planets in the universe.”
David Holmes.
Much water
But, in his opinion, what is most fascinating and which has also been recently corroborated, is that in the process of planet formation there is a lot of water and also a lot of carbon. And that is precisely what we are made of. “Perhaps life is assured, my bet is that life will be found and I also believe that that life will be based on carbon and water.”
He recognizes that while other possibilities cannot be completely eliminated, carbon is definitely the most favored because it can form stable bonds, while silicon, which is very similar in many ways to carbon, tends to form rigid structures, such as quartz, rather than the complex, flexible molecular structures that carbon forms in organic compounds, “So I would put silicon aside and focus on carbon.”
– Could there be other different chemistries in the universe?
– A common chemistry is one of the distinctive universal features of the cosmos and is supported by scientific evidence. The universe creates hydrogen from its origin. When it explodes at first in the Bigbang, the elementary particles form hydrogen, but then it moves up the periodic table and becomes helium, and then lithium, and so on. And then all this condenses into stars. The stars begin to burn, and the enormous pressure at high temperature causes the hydrogen to convert to helium and back to lithium. Then we have atoms like sulfur, and eventually iron, and even incredibly heavy elements like lead and others that definitely come from stellar explosions. And these stellar explosions, which we know occur in all galaxies in different parts of the universe, and yet they are the same chemical elements that are being formed. Hence, I am in favor of a life based on carbon, nitrogen, sulfur, phosphorus and oxygen.”
– And how can we try to discover this life now? What are the techniques we are using to try to find it?
– In the case of extrasolar planets we are not going to get there so we have to do it with telescopes, including those in Chile, which can cover the spectrum of the atmosphere of those worlds. The technology is becoming so sensitive that they will soon begin to detect chemicals in the atmosphere of these exoplanets. Water is a fairly easy signal to detect and the presence of oxygen in the atmosphere could be an indicator of life.
Initially, Earth’s atmosphere had no oxygen because oxygen, although abundant, is so reactive that almost all of it was consumed in reactions with minerals, life evolved anaerobically and was confined to simple microorganisms such as bacteria and archaea. It took more than two billion years for photosynthesis to evolve and oxygen to accumulate in the atmosphere. So the presence of oxygen in an exoplanet’s atmosphere could be a strong indication of the presence of life.
A third biomarker that has been mentioned is methane, which is produced by anaerobic microorganisms on Earth. However, it can also occasionally occur abiotically, that is, without the presence of life. “Therefore, although methane is a signal that must be attended to, it is not exclusive to living beings as oxygen is.
– What are the challenges of Astrobiology? What is your projection?
– Borrowing the phrase attributed to Yogi Berra, it is very difficult to make predictions, especially about the future. But anyway, I think we are on a very positive path. In the last 10 or 15 years, we have gone from knowing one planet outside our solar system to thousands of them and that is going to continue with new telescopes in operation such as the Giant Magellan Telescope (GMT), the Extremely Large Telescope (E -ELT), plus Kepler, Hubble, and James Webb. These will continue to refine our ability to identify planets in the habitable zone of stars. In my area of research, I think we will continue to learn how Extremophiles survive, leading to whether they could be found on other planets and moons in environments that would be considered extreme on Earth. Furthermore, they leave “biomarkers” of their present or past existence.
The presence of complex organic molecules, such as amino acids, nucleic acids and other biomolecules, could indicate the existence of life. These molecules can be detected through spectroscopy (the study of the interaction of electromagnetic radiation with matter) during the search for life on Mars, Enceladus and Europa. It will likely be necessary to combine multiple lines of evidence and employ diverse scientific approaches to confidently identify biomarkers on other planets and moons. In addition, it is essential to consider the geological and environmental context of each celestial body to avoid false positives. I just hope it is still alive when they discover life for the first time.
When I referred to the enormous number of exoplanets, I did not mention the moons. If we have 10 to the power of 23 exoplanets, perhaps we have 10 to the power of 25 moons, a percentage of which could be rich in life. It’s simply amazing.
Until a few years ago I believed that there was no possibility of life on them, particularly those in the solar system like Europa and Enceladus, because they were too far away and frozen. But no, the gravitational force causes the ice to melt and life could most likely be at the bottom of your ocean, so it’s very exciting. And those moons are within our range. So we will know, I think within a decade, maybe two, if there is life on those moons. This could be repeated in worlds beyond the Sun.
It will be extraordinarily difficult to find extrasolar moons considering how difficult it was to find planets. But new telescopes may have such resolution that they will be able to find at least the largest ones.
Another variable that we must consider when we search for life on other worlds: time. The existence of humanity and planet Earth is concentrated in a small window of time. That’s a small amount of time on a universal scale. There are many, many planets and many suns that are much older than us. And we know that some of those planets are quite stable. If life developed there and became intelligent, those intelligent beings have had millions of years to evolve further. So where did they evolve? One possibility is that they evolved into computing robots, artificial intelligence robots. So even if they still have organic parts, I don’t know, they are going to be essentially robotic. So where are they? Are we too small, too uninteresting for them? Are we in too small a window of time to be contacted by them? So we have to think that maybe life becomes so intelligent that we no longer recognize it. So we are looking in a certain window of time for the things that we know to look for.
– Artificial intelligence is steadily increasing its presence on Earth. Perhaps we are the last biological generations, and in less than 100 years we will become digital life, beings that transport their minds to electronic devices to transcend. What do you think about this?
– I agree, but I would suggest that perhaps it could be more than a hundred years, perhaps we could talk about at least a thousand years. That is a possible line of evolution for organisms on other planets. At some point in the future humans could adopt an electronic robotic lifestyle or perhaps a mix of both.
– But is that also life or not?
– Well, I had an argument with my daughter about that. I tested ChatGPT under the following conditions. There was an image of a robot holding a skull with a background of devastations and volcanic eruptions, etc. So it was obviously a robot holding the last human skull on Earth. So I told ChatGPT: Please write some Shakespeare-style verses about poor Yorick based on this image (the scene from Hamlet in which the prince of Denmark reflects on life while holding the skull of his friend, the jester of the same name, whose body had been exhumed). ChatGPT came back with something that was absolutely pure Shakespeare. It had the rhythm, the sounds and the thoughts of Shakespeare. That surprised me. So I sent it to my daughter who likes the subject, and she said: Well, yes, but he’s not alive. And I started thinking about it, and eventually I might be alive. What do we mean by being alive? We have neurons buzzing, so we’re sensitive to our surroundings, we’re talking together, and we’re sensitive to that, and we feel things. Why couldn’t a robot eventually have those same capabilities? I think so. But I believe that the transformation into a digital being will take us more than a thousand years.
