I'm primarily concerned with the Western front. I have read that most of the standing and mobilized armies in Europe were extremely worn down by just the first couple of months, and that they fairly quickly had to call in badly trained reserves.

But, I have also read that soldiers were much more likely to die at the start of their assignment to the front, i.e. when they were green, than later.

So, how many soldiers of the armies that were used in the initial assaults actually survived the entire war? Did most die and were just continually replaced or what?