Subject: Can we mathematically estimate how long evolution should take?

It seems that the process of evolution requires a certain amount of time, 
for all the mutations, some species dying, others surviving, etc.  I am 
wondering if there is any mathematical way to estimate how long this 
should take, from amoebas to humans (how many necessary mutations, the 
odds of each one, the length of a generation, etc).  Then, how does this 
number compare to the history of life on Earth?  I am a firm believer in 
evolution, but this seems like a fair question, and would help respond to 
the nagging question "how could purely random mutations create scuh 
complex beings?"

Re: Can we mathematically estimate how long evolution should take?