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Scientists are looking for an earth-like habitable exo planet. If an exo planet is earth-like (in terms of gravity, atmosphere, light, water etc.), then it must have gone through an evolution process (hot gas fireball to present earth), which means that there must have been some chemical processes creating DNA.

Isn’t it must that every earth-like habitable exo planet have some kind of life-form and ecology already present?

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  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Jan 9, 2022 at 10:26
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    $\begingroup$ If the planet is sufficiently Earth-like to have free oxygen in its atmosphere, then it is certain that it has life; because free oxygen is a highly reactive gas, and cannot exist in the atmosphere of a planet unless something is replenishing it constantly. If all plant life on Earth died, the oxygen in the atmosphere would surely find something to oxidize and would be completely gone in short time, geologically speaking. (Not so short a time on human scales, of course, but what are a few million years in the geological history of a planet?) $\endgroup$
    – AlexP
    Commented Jan 9, 2022 at 10:28

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Similarly structured alien life is dangerous

Don't overdo the search for a matching planet. When it is too similar, that is already hosting life, your project could fail..

1. Planet already occupied ? Watch your step !

When life exists already, some of the life forms you find could be intelligent, humanity infringing upon their Galactic Right to survive.. or the colony could already be occupied, by other colonizers from elsewhere. For the issues that could arise with that, ref How to keep the peace after an attempt to colonize an inhabited planet?

2. Too good: when it has DNA, biome incompatibility results in toxicity everywhere

Suppose life on your inhabitable planet is based on CHO, and organisms have DNA, or DNA-like molecules with a similar function.

Your safe and viable agriculture will have to be completely isolated from the planet's biome. Any area used for agriculture must be disinfected first, killing all local life. Reason: many genetic incompatibilities will render alien life toxic for humans. Humans would have to remain in isolation. Extinguishing the alien biome (also deep underground) outdoors could be far more difficult than isolated, biosphere-based agriculture, as performed on a lifeless planet. You'd probably need the same facilities, at first..

Even if your planet's properties seem perfect, you can't expect Earth

A perfect Earth copy will do of course.. but you won't find that. A planet in the Goldylock zone, which looks less comfortable, that is without any life, say Mars-like, will be more appropriate for colonization. Agriculture in isolated/protected environments would be safe. Meanwhile, humans could terraform the planet by introducing water, CO2 and plant life. Terraformation will take time, but in the end, you'd have a greenhouse and O2, resulting in an Earth-like biome and working agriculture outdoors.

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Short answer is no. We don't know yet exactly what chemical processes could create DNA. Or how this process is triggered. It is possible that you have all the right conditions but not the exact right chain of events to trigger the reaction. Even if you did what's to say that DNA would evolve into a full ecology. It could just as easily be destroyed long before it has time to evolve into anything.

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