The obligate aerobes need oxygen for their survival, while the obligate anaerobes do not. The obligate aerobes are the species that attain the energy for the process of aerobic respiration with the help of oxygen as the ultimate electron acceptor for the electron transport chain.
On the other hand, obligate anaerobes are the species, which get poisoned by the usual levels of atmospheric oxygen, and thus, get killed in the existence of oxygen.
1.5billion I don't know don't be so harsh?
Answer: It is a carbon residue left by a decaying organism.
This picture of the fossil is different from other fossils in terms of its impression. This is an example of compression fossil which is formed by the compression of something on it. The leaves of the tree got stuck on the rock and created an impression on it.
It is different from other fossils in the terms that it does not contains the actual part of the organism, it is just an impression.
