Geobiologist Alexis Templeton thinks it matters:
We humans tend to see the world as a solid rock coated with a thin layer of life. But to scientists like Templeton, the planet looks more like a wheel of cheese, one whose thick, leathery rind is perpetually gnawed and fermented by the microbes that inhabit its innards. Those creatures draw nourishment from sources that sound not only inedible, but also intangible: the atomic decay of radioactive elements, the pressure-cooking of rocks as they sink and melt into the Earth’s deep interior—and perhaps even earthquakes.
And the implications for finding life on Mars?
Finding that life will be a challenge. With existing technologies, a probe sent to Mars could drill no more than a few feet below its hostile surface. Those shallow rocks might contain signs of past life—perhaps desiccated carcasses of Martian cells, sitting inside the microscopic tunnels that they chewed into the minerals—but any living microbes are likely to be buried hundreds of feet deeper. Douglas Fox, “Meet the Endoterrestrials” at The Atlantic
The fact that many life forms in these extreme environments live on hydrogen suggests that the earliest organisms did so. But we might do well to be careful here: It could be that these organisms devolved from life forms with more complex diets because that is how they survived in these places (devolution).
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See also: Researchers: Horizontal gene transfer may have helped early microbes move out of hot springs
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ET life might be huddled under hydrogen blankets