A traditional circular argument used by creationists is that this planet must be perfect because it was designed by their god; they know it was designed by their god because it's perfect. They call this the 'Goldilocks' argument and seem jolly pleased with it. Basically, they seem to inhabit a fantasy Panglosian world in which everything is for the best in the best of all possible worlds - if you ignore all the bad bits and imperfections.
But a new study by René Heller of McMaster University in Hamilton, Ontario, Canada, and colleagues has shown that, far from being perfect for life, this planet could have been very much better and in ways which shouldn't have been at all difficult for an omnipotent creator who made the Universe. In fact, these planets may be fairly common in the Universe.
To be habitable, a world (planet or moon) does not need to be located in the stellar habitable zone (HZ), and worlds in the HZ are not necessarily habitable. Here, we illustrate how tidal heating can render terrestrial or icy worlds habitable beyond the stellar HZ. Scientists have developed a language that neglects the possible existence of worlds that offer more benign environments to life than Earth does. We call these objects “superhabitable” and discuss in which contexts this term could be used, that is to say, which worlds tend to be more habitable than Earth. In an appendix, we show why the principle of mediocracy cannot be used to logically explain why Earth should be a particularly habitable planet or why other inhabited worlds should be Earth-like.
Superhabitable worlds must be considered for future follow-up observations of signs of extraterrestrial life. Considering a range of physical effects, we conclude that they will tend to be slightly older and more massive than Earth and that their host stars will likely be K dwarfs. This makes Alpha Centauri B, which is a member of the closest stellar system to the Sun and is supposed to host an Earth-mass planet, an ideal target for searches for a superhabitable world.
Heller, René and Armstrong, John. Superhabitable Worlds, Astrobiology. January 2014, 14(1): 50-66. doi:10.1089/ast.2013.1088.
Of course, the simple facts and inevitability of evolution are perfectly adequate for explaining why life appears to be more or less perfectly adapted to the present conditions on Earth, without the need to invoke magic, but living things being very well suited to the conditions in which they evolved is not at all the same as those conditions being perfect for living things to live in. Evolution can mold a species to the environment but it can do nothing at all about the planet itself.
Evolution can't influence gravity or the magnetic field of the planet, or what meteorites might smash into it. Nor can it affect the process of plate tectonics or the rate at which the sun is burning up its fuel, nor what will become of the planet when the sun blows up.
In fact, evolution of life can only influence the evolution of environments to a limited extent and none of it can be planned and made the purpose of evolution, so Earth has many environments such as arid deserts, arctic icecaps, permafrost, snow-covered mountain ranges and deep ocean trenches where only highly specialised organisms can exist and where life, for the most part, is a rarity and where life for most of Earth's species would be impossible.
But, a planet perfect for life would be one where life was abundant everywhere, where the planet had a longer life in which evolved life could flourish and mature. The environment would be such that basic maintenance activities like respiration, body temperature stability, etc took minimal effort, and the planet would be protected from meteorites, comets and dangerous solar radiation.
René Heller and colleagues analysed a range of factors which could have produced a better planet for life. For example, Earth is not in the centre of the habitable zone around the sun as creationists like to pretend. In fact it is close to the inner edge of this zone. As the sun gets hotter, in the next 1-2 billion years, Earth will become a hot, uninhabitable rock like Venus. Life has been on Earth now for about 3.5 billion years so we are already well beyond halfway to heat-death extinction even if Earth manages to survive a runaway greenhouse effect.
Had Earth been a little larger and orbiting an orange star it could all have been so much better. The star would be around for about 7-10 billion years instead of the 5-6 billion we get. The higher gravity would have meant shallower seas and low, rounded hills on chains of islands in warm seas - exactly the conditions which have the highest biodiversity on Earth.
A slightly higher gravity would have made the atmosphere a little denser, so it would have been easier to take in oxygen and respiratory systems could have been smaller and taken less effort. Flight would have been easier for larger creatures. It would also have increased plate tectonic activity without dramatic and destructive earthquakes, tsunamis, volcanoes and upheavals of mountain-building that Earth has experienced. This, in turn would have increased the core temperature and the magnetic field, so helping to deflect dangerous solar radiation.
We already know that the orange star, Alpha Centauri B, our sun's nearest neighbour, hosts a rocky planet which is already 6 billion years old. This planet is probably too close to its sun to host life but we are now discovering that exoplanets (i.e. planets outside our solar system) are common. There were clearly very many far better planets the creationists' supposed creator could have put us on.
I wonder if any of them can explain why he didn't. I don't suppose it's anything to do with the authors of their favourite book of facts not knowing there were other suns and planets for it to choose from or better ways of constructing this one to make it more suitable for life.
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