Obviously plants and bacteria would be considered life. But we've never detected plants or bacteria on other planets, or any other life. When you hear about "earth like " planets they're only talking about the planets size and how much energy it receives from its star, because that's all we can know about them.

If we knew there was vegetation, that would be proof of life. Plants are alive.

But we can't see exoplanets in enough detail to detect these things. The closest we can get is detecting the composition of the atmosphere.

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Bacteria would constitute life.

Having bodies of water does not.

A 15% to 30% oxygen atmospheric content would be a pretty good indicator of some sort of life.

I believe when scientists mention ‘earth type’ the only variable they are referring to is distance from the host star to be able to support life. If life exists or existed…?

Speculations of life perhaps but proof would require observing some form of life, which hasn't happened quite yet

> bodies of water

Not proof of life. Just a far better chance that life exists, as we know it.

> vegetation on land

Proof of life. Plants are considered as living things because they fulfill all the characteristics of living things.

Plant life began began colonizing land 500 million years ago, during the Cambrian Period, around the same time as the emergence of the first land animals.

Microscopic organisms (microbes) left signals of their presence in rocks about 3.7 billion years old. Microbes would also be considered life as microbes are social creatures that live in communities shaped by cooperation and competition, and they change their behavior, sometimes for the worse, depending on the company they keep.

Keep in mind that Mars and Venus would both be counted as "earth-like exoplanets" if we spotted them from similar distances.

We haven't seen any chemical signatures that are unique to life in any exoplanet atmospheres so far afaik - but that's not saying much since numerous biological processes mirror geological ones but just go faster, at least in terms of processes that produce enough gases to show up in atmospheric absorption spectra.

In short, we have no evidence that cellular life (let alone anything bigger) exists on other planets - but also no evidence that it doesn't, due to the limited abilities of our best instruments.