For example, modern horses evolved over millions of years from what looked liked smaller horses. While the small ancient horses are in the same direct lineage that provided today's big horses, they are not considered the same species. With that in mind, I can answer your question. And even though such microbes have evolved slowly, they are still only today's descendants of ancient organisms. But this is the best we have for guessing what the ancient organisms actually looked like.
Many scientists believe the hyperthermophile lineages reflect the first organisms on Earth.
Likewise the early ocean was probably hot and had no oxygen, which are both consistent with the conditions almost all hyperthermophiles need to live. So, the beginning of the lineages that lead to today's hyperthermophiles may be almost as old as the Earth. As for other vent microbe species, they ultimately are all descendants of the first hyperthermophiles. One can follow the diversification along the tree of life with similar genetic information, but it's difficult to pinpoint the time when the varied lineages actually began. I really had no idea what I was going to do when I began college other than it would involve science and math in some way.