Here’s a simple math exercise for you:
Suppose aliens come and want Earth intact but kill off all the troublesome humans. How big a hole would they need for a mass grave big enough to dump every body on Earth into ?
They’d need a hole the size of the Grand Canyon.
Fortunately for them, God knew they’d be coming and made advanced preparations.
My first thought was that Meteor crater might do.
The "average" human is say 1.6m tall, 0.5m wide and 0.25m thick giving a typical body volume of 0.2m3 times 6,000,000,000 gives a volume of 1.2km3.
Assuming Beringer Crater is a cone (it actually has more volume) it is 1.6 km diameter, and 190m deep giving a volume of 0.12
That ain't gonna work.
A conical hole 3Km in diameter, and 0.5km deep would do.
OTOH They could just as easily render us all down for oil...
I estimate the corpses of all 6 billion human beings contain less cubic feet of space than a hole 1 mile X 1 mile X 1 mile.
But then again, it is pretty late for me. I could be wrong.
BTW, why ask that question?
I read somewhere that all the 6 billion people in the world could fit into the state of Texas, with plenty of room to spare for everyone. Don’t know if I would like to see that many people in Texas, though...
They’d need a capacity of at least 6.3 billion. Humans are troublesome practically by definition.