Prokaryotes: Prevalence of Prokaryotes

Prokaryotic cells are incredibly abundant and diverse, found in various environments from soil to extreme conditions like hot springs and deep ocean beds. There are thousands of known types, with many more yet to be discovered. In the 1970s and 1980s, new findings led to a reclassification of prokaryotes into two major groups: archaea and bacteria. These groups are the oldest and simplest life forms on Earth, yet they are the most abundant.

What are the two major groups into which prokaryotes are divided?

Why are archaea and bacteria considered the simplest organisms on the planet?