Originally Archaea was thought to be part of Bacteria, and was thought to be the most ancient group of bacteria. Because of this they used to be called Archaebacteria, however with modern advancements in gene sequencing the scientific community has realized that they shouldn't be part of the bacteria Kingdom. The reason for thinking that they were an ancient kingdom was that they have adapted to living in some of the harshest environments on the planet1.. Because of this they were only broken out of the Prokaryots group in 19773.. Currently we think we Know about 377 of an estimated 502 living species2..
Discovery:The first place we observed Archaea was actually in the hot springs of .Yosemite National Parkeven if they were only a few meters apart. Another area where they were discovered flourishing is inside of deep sea thermal vents, some can even survive in areas of radioactivity. Because of locations like those mentioned above they are often considered extremophiles, however not all members of Archaea live in such extreme environments1.. Even though we have learned a lot about archaea in the past 40+ years they are still one of the most mysterious kingdoms on this planet, and their is still plenty of research to be don to learn more about them.
If you were to look at an Archaea and a bacteria under a microscope you would be forgiven for thinking that they were the same as bacteria because visually they are very similar (this is another part of the reason they were originally considered bacteria). LIke bacteria they don't have organelles or interior membranes or a nucleus, they usually have their cell membranes attached to a cell wall. Some also use one or more flagella to move around similar to bacteria3.. However genetically they vary greatly from bacteria on account of their adaptations to survive such hostile environments.
Reproduction:Because Archaea don't have nucleus to undergo reproductions like mitosis, and because of this they also don't release any spores. They do however undergo a process called Binary Fission, this is a form of asexual reproduction. Because Binary Fission is a form of asexual reproduction they exchange genetic material through a process called Horizontal Gene Transfer3..