What is drive Level? What are the effects of excessively high drive level?

A.

Drive level is the power applied to the crystal by the oscillator circuit.
The drive level can be calculated as follows:
​where I is the current entering the crystal unit, and Re is the effective resistance of the crystal.
Additionally, Re can be estimated as: If the drive level exceeds the specified limits significantly, that will cause no oscillating, frequency deviation, or higher resistance. It is recommended to incorporate a current-limiting resistor (Rd) in the design or to use XTAL with a higher drive level specification to avoid the crystal operating beyond its limits.