I understand he wants to kill half of the population in each planet, but:
* Are the lifeforms going to be like half of each species by individual, by the kilo..?
* Or will it be half of the total life, so it wouldn't matter how much of each species is present?
* Is he considering viruses a form of life?
* Will be half of each age, for example half of kids, half of adults, half of old people..?
* Will it be randomized in terms of location? For example, half every x square meters?

So many questions...