This picture above shows the simple and broad diagram of what a Archaea cell would look like.
Archaea was not always its own Domain. It used to be a kingdom combined with Bacteria called archaeabacteria. It now is its own independent Domain.
It has many biochemistry differences to other organism life. Since the differences were so great, it is now known as the ThreeDomains. Classifying Archaea stayed difficult, since most of the organisms have never been studied in the laboratory. They were only looked at throughthe analysis of the archaea’s nucleic acids in the environmental samples. The vast majority of Archaea have never been discovered compared to the other Domains.
Archaea are found to be the oldest organisms found on Earth. The Theory of Endosymbiosis says that life evolved from the Archaea. The oldest Archaea found dated back 3.5 billion years. Since Archaea are only prokaryotes and prokaryotes do not have displayed morphologies, the fossils are hard to categorize as Archaea. Therefore, lipids are used to detect if the fossil could be Archaea or not. 
Below are two different organisms that could be found in this Domain. Click on them to learn about different organisms that are classified in Archaea.
Check out another domain by clicking the button below :)