Why are scientists who are searching for life on other planets studying archaebacteria? (i already know the answer but this is here because i didn't see it for anyone else)
a. they are similar to organisms found on other planets.
b. they live in conditions similar to those likely found on other planets. (this is the answer)
c. they are rare and abundant on other planets.
d. they are the easiest cells to study without using a microscope.

B. They live in conditions similar to those likely found on other planets.

Explanation:

Archaebacteria involve those bacteria that live in extreme conditions. For instance, halophiles are those species of organisms that live in extreme salty conditions. Archaebacteria are obligate anaerobes that do not require oxygen for its respiration.

Scientists are not sure of the presence of oxygen in other planet and studying the possibility of archaebacteria existing in other planet is higher than other organisms because other higher organisms require proper environment condition for their survival.  

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem