Following up my earlier post, I've been doing some back of the envelope math and here's what I've come up with.
1 gram of antimatter annihilating 1 gram of ordinary matter would release 3 times the amount of energy as the Hiroshima bomb (per Wikipedia). There are 1,000 grams in kilogram.
Therefore, annihilating 1 kilogram of antimatter would release 3,000 times more energy than the Hiroshima bomb. This would exceed the largest nuclear bomb ever, the Tsar Bomba, which released about 1,500 times the energy of the Hiroshima bomb.
Say you take a person of ordinary build who weighs 70 kilograms (154 lbs.). If you took 70 kilograms of antimatter and used it to annihilate that person, the result would be an explosion 210,000 the size of Hiroshima.
That's not enough in and of itself to blow up the Earth. The asteroid that killed the dinosaurs is thought to have released a billion times more energy than the Hiroshima bomb, but the explosion would be roughly 140 times bigger than the largest nuclear weapon ever detonated.
This is just for one person. Freddy was apparently talking about using antimatter to annihilate the remnants of the "old system." It's possible you could quickly start approaching scales that would blow the Earth into pieces.