Archaebacteria are able to survive in harsh conditions because of branched lipid chain in the cell membrane which reduces the fluidity of the cell membrane. Archaebacteria are the oldest organisms living on the Earth. They are unicellular prokaryotes and belong to the kingdom, Archaea. They were first discovered in 1977 and classified as bacteria. Most archaebacteria appear like bacteria when observed under the microscope. However, they are quite different from bacteria and eukaryotic organisms.