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I've never understood applying this idea to exoplanets. What if the life there puts sulfur into the atmosphere instead of oxygen? Why would the life elsewhere l

• marcellus23 2y ago
  The point is that if a planet has oxygen, it's a potential marker for life. No one is claiming that a planet that lacks oxygen in the atmosphere must necessarily be lifeless.
• joshuahedlund 2y ago
  It's true that if life exists on other planets, it may not look exactly like life here. But it's also true that there are a small number of elements in the periodic table, and only so many of those are even relatively common in the universe, and only so many of those are useful for reactions, etc, etc. The things that life on our planet use seem to be some of the most obvious candidates to use, if not the most obvious, so if life exists on other planets, it would be surprising if the things that we use are unique or even uncommon across the universe.
• idunnoman1222 2y ago
  Bc the same physics apply there