We might compare the vast and hostile expanse of space with the deep ocean floors of the Earth. They take up vast regions of the planet’s surface, and they have never seen sunlight. They are underwater continents of crushing pressure and constant darkness.
It’s a place that for the most part is totally empty of any form of life, being too dark, too cold, and too high in pressure to be hospitable.
However, spread thin throughout this underwater world are small cracks in the Earth's crust. When this happens, magma mixes with cold seawater, heating it from 60-400°C. Minerals released from the magma solidify around the points of contact, eventually creating layers of sediment that form a chimney-like structure on the deep ocean floor, from which jets of smoke erupt. Some have been discovered to be 15 stories high.
On these underwater structures, called hydrothermal or deep sea vents, entire ecosystems of life have evolved. They feed on the minerals of the vents and bask in their heat, and have complex communities of life just like any other ecosystem, but are totally dependent on their vent.
The hydrothermal vent occur so rarely in the vast underwater landscape of the deep ocean, and the distances between them are so vast, such that the life living on one deep sea vent have often evolved totally independently of one another over periods of millions of years.
To reiterate: None of the creatures on one deep sea vent have any connection or awareness of other vents, of other ecosystems living on any of those vents, or even of the rest of the world existing.
An ecosystem of life, including crabs, shrimp, and mollusks on a deep sea vent. They are all white as their bodies do not waste energy creating pigmentation, when there is no light other than what comes from the occasional submersible.
These ecosystems can be considered to be metaphors, for life existing on planets orbiting stars, pinpricks of energy in the vast darkness of interstellar space. Without incredible technology, forms of life will evolve independently, unaware of each other, and never crossing the vast chasm of space separating them.
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