The Problem Is Not the Template. It Is Having Only One.
Kai Finster at Aarhus University was precise about this in our conversation. Astrobiology uses Earth as its model system not because scientists lack imagination, but because Earth is the only confirmed example of life that exists. You cannot build a detection framework around things you have never observed. If you want to design an instrument to look for life on Mars, you need to know what you are looking for, and the only evidence you have for what life looks like comes from here.
This is not a failure of the field. It is a constraint imposed by the problem itself. The criticism essentially asks scientists to search for something they cannot characterise, using criteria they cannot define, with instruments calibrated to detect nothing in particular. That is not a more open-minded approach. It is no approach at all.
The deeper issue is that Earth's biochemical solutions are probably not arbitrary. Water is not the solvent for life on Earth because life on Earth happened to like water. Water has physical properties, including its heat capacity, its behaviour as a solvent for ions and organic compounds, its role in spontaneous membrane formation, that make it extraordinarily well-suited to supporting the kind of organised chemistry that life requires. Kai put it plainly: "If you need a solvent, this is a very common solvent. So it's the most common solvent in the Universe."
Those properties are not Earth-specific. They are consequences of water's molecular structure, which is the same everywhere in the universe. The argument that we should not use water as a search criterion because it is Earth-centric is equivalent to arguing that we should not look for carbon chemistry because carbon is the most common reactive element in the universe. The ubiquity is not a bias. It is the reason the search is scientifically justified.
The Counter-Argument and Why It Survives Poorly
The strongest version of the critique is not that we should abandon Earth-based criteria entirely, but that we should hold them loosely and remain alert to life that looks sufficiently different that our instruments would not flag it. That is a reasonable caution. It is also largely what the field already does.
Astrobiology does not claim that life must use water, or that it must be carbon-based, or that it must have DNA. It claims that these are the most probable solutions given what we know about chemistry and physics, and therefore the most rational places to start. The ExoMars mission's primary goal is not to confirm that Martian life looks exactly like Earth life. It is to find organic compounds. If something organic is there, the next question is what kind. That is an open question, not a closed one.
The critics are essentially demanding that science skip to a level of openness that requires no assumptions. But science runs on assumptions. The method is to make assumptions explicit, test them, and revise them when the evidence requires it. Using Earth's biochemistry as a starting template is an explicit assumption. Finding life on Mars that uses mirror-image amino acids would revise it. Finding life that uses no amino acids at all would revise it further. That is how the method is supposed to work.
What Is Actually at Stake
Kai made a point that I keep returning to. If Mars life is found and it uses the same biochemical solutions as Earth life, that result is at least as significant as finding life that looks completely alien. Because it would mean that those solutions are not contingent on Earth's particular history. They are the solutions. Water works, membranes work, DNA-like information storage works, because they are probably the best available answers to universal problems that any form of life must solve.
That would not be a disappointing result. It would be a deeply clarifying one. It would tell us that the universe is in some sense biased toward a specific kind of chemistry, that life, wherever it arises, tends to find the same tools. The implications for how common life might be would be significant.
The alternative, life using completely different chemistry, would also be significant, and for different reasons. It would tell us that there are multiple viable paths, that life is more inventive than our one example suggests, and that our search criteria may need to expand dramatically.
Both outcomes are worth pursuing. Both are best pursued by starting from what we know. The criticism that astrobiology is anthropocentric mistakes the starting point for the conclusion. The field knows it is reasoning from a sample of one. That awareness is not a blind spot. It is the central intellectual challenge that makes the work interesting.