The Most Astounding Fact (Neil DeGrasse Tyson)

[saras]

2. "Life" in that case, may mean bacteria miles down in solid rock.

With a reasonable combination of chemical, biological, and nuclear weapons, we could pretty much eradicate multicellular life from the planet. We'd have to explicitly target important systems like the ionosphere and deep oceans rather than just big cities, but I think we could do a pretty thorough job. Remove the ozone layer with the longer-lasting gases, ramp up the production of the more effective greenhouse gases, poison the country's major aquifers, strip the vegetation with long-lasting poisons, vaporize a few thousand tons of plutonium into the air...

I think he vastly underestimates the damage we could do if we really set our minds to it.