The earliest known life-forms on Earth are fossilized micro-organisms, found in hydrothermal vent holes in the seafloor. These were most probably chemosynthetic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material. Scientists have also recently found that hydrothermal vents at the bottom of the ocean are hot enough to emit enough light (mostly in the infrared spectrum) to support photosynthetic bacteria.
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