It was critical.. As you know cells are microscopic and cannot be seen with the naked eye. Without a microscope it probably wouldn't have been discovered.
The right answer is compression.
There are basically two types of constraints that deform rocks: compression and tension constraints. In compression, forces converge; they can be coaxial or not.
The deformation of a card set under compression constraints illustrates the difference: In the case of a coaxial compression constraint, the cards will be arched. If the stresses are not coaxial, shear will develop; the card game is deformed by sliding the cards on top of each other:
<span>the bird will hibernate instead</span>
