Some forms of bacteria are known as Archaea
Click on image for full size
To date, the oldest known life forms are certain types of bacteria that have been found in
Australian rocks that date back 3.5 billion years ago. At this time, oxygen was not present
in the Earth's atmosphere, thus these bacteria must have been anaerobic.
These bacteria have been found within rock itself, miles underneath the surface.
Bacteria such as this give off ammonia as a waste product. Thus one way to detect increased activity by such creatures is to measure levels of nitrogen in the atmosphere.
This is page 5 of 20
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games