Is that still the case with the discovery extremophiles that exist on chemical vents deep under the ocean and far away from the sun? Or rather, how sure are we that they're the same form?
Yes. All known life shares an (assumed) last common universal ancestor (LUCA, presumed extinct), and there is significant evidence pointing that way.
We can infer properties and function by looking at genes shared between archea and bacteria that most likely came from such an ancestor; this paints a picture of a DNA-based anaerobic thermophile (think hydrothermal vents) with a membrane and simple anti-virus defenses (CAS).
