There are plenty of things we can’t kill and, in fact, live on things we might use to kill them. Extremophiles that live in environments nothing else can. Bacteria that live off gamma radiation. We would have to dedicate ourselves to ridding all life on purpose to kill everything. We would have to live long enough to be the last things to kill if that was the goal.
True, it would be difficult to completely turn Earth into a lifeless rock, but I think humans are up to the task.
There are plenty of things we can’t kill and, in fact, live on things we might use to kill them. Extremophiles that live in environments nothing else can. Bacteria that live off gamma radiation. We would have to dedicate ourselves to ridding all life on purpose to kill everything. We would have to live long enough to be the last things to kill if that was the goal.