Over the last few years, the universe has started to look increasingly friendly to life, and scientists who previously said they didn’t expect to find living things on other planets are beginning to change their tune. NASA’s Kepler telescope may be largely non-functional, but the search for other organisms in the Universe is just beginning.
Last month at the Faraday Institute, astrobiologist Stephen Freeland gave a lecture entitled, ‘Will alien life share our genetic code?’ – a topic which would have been on the border of science fiction a couple of decades ago, but is now a serious question.
Estimates of the number of planets in the universe that support life, the most famous of which is the Drake Equation, focused on a number of factors including
- The number of stars in a galaxy.
- The fraction of those stars which are orbited by planets.
- The fraction of planets per star that can support life.
- The fraction of planets where life evolves.
There are billions of stars in the universe, so number 1 isn’t the limiting factor in this equation. Until recently it was thought that low results for 2 to 4 meant life on Earth was unique, but those estimates have been changing. Recent studies by NASA have revealed many stars in our galaxy that are orbited by planets, some of which might be like ours. Even more interestingly, planets may not need to be Earth-like in order to support life.
We now know that life is more diverse and more tolerant of extreme conditions than people used to think. Acidic pools, hot volcanic lakes, deep-sea vents or oxygen-deprived areas are teeming with life. The organisms you find in those deep, dark or dangerous places might look a little different to what we’re used to, but they’re definitely thriving. Knowledge of these hardy species goes hand-in-hand with the developing idea that life seems to have started on Earth much earlier that previously thought. Estimates of the date for the earliest life are homing in on 3.9 billion years ago (the Earth is thought to be about 4.5 billion years old): a time when environmental conditions were very extreme.
We also know that living things are made largely of some of the most cosmically abundant elements (Carbon, Nitrogen, Oxygen, Hydrogen, Phosphorus and Sulphur) arranged in fairly ‘obvious’ combinations. Around half of the amino acids in our bodies are also found on meteors that rain down on planets all over the universe. The other half looks like a collection of derivatives of the meteoric ones. With today’s calculation of the Drake equation, it might be that the number of planets that contain life could be considerably larger than one!
The most interesting question to us is not just whether life might evolve on other planets, but might intelligent organisms emerge? That’s a difficult question. According to Freeland, the orthodoxy of the last century was that the evolution’s outcome is completely unpredictable. Stephen Jay Gould famously said that (if I can give an updated version of his analogy) replaying the game of life on Earth would result in a different outcome every time. So can we tell whether an evolutionary process on a certain planet would produce sentient life?
The twenty first century challenge to scientific orthodoxy has been led by individuals like Simon Conway Morris who have pointed out that different evolutionary pathways tend to converge on similar solutions, like a bullet shape for swimming through deep water or camera eyes (ones with lenses like ours) for seeing. Convergence happens because the process of natural selection transfers information from the local environment to DNA. Mutations may happen fairly randomly, but the ones that survive are the ones that make sense in the local conditions. In other words, evolution does not create information, but reflects what is already present in the universe.
Freeland’s research has shown that if there is life on other planets, it may use a very similar genetic code to ours (if not completely identical). Why that might be, is explained in my previous blog, Wonderful Code. He is less confident than Conway Morris about the degree of predictability to evolution, that doesn’t mean it’s going nowhere. If conditions in the universe are similar, then maybe life’s solution will be recognisable on other planets?