What group of archaebacteria live on the surfaces of swamps, marshy lands, and intestines of cows?

Methanogens or methane producing bacteria.

Explanation:

This bacterium uses carbon and hydrogen as a carbon and energy source to metabolize and produce methane. Methanogens are halophiles, meaning they flourish in environments that have a high salt concentration. This bacterium play a vital role in the ecosystem by removing excess hydrogen from the air produced during anaerobic respiration.

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