| As everyone knows, the toxic molecule DHMO is all around us. Also, the very air we breathe is toxic. However, the link between the two is relatively simple - the deadly process known as photosynthesis.
Way back when, before the dinosaurs, life happily munched on safe hydrogen sulphide or even hydrogen itself. At some point, the evil technology was invented by some cunning algae out to destroy the world. Instead of splitting safe fuel, the potentially destructive 'water' was used to provide protons. This inevitably produced oxygen as a toxic byproduct.
Although tolerable for a while (couple of million years?), the inevitable result was mass extinction of the peaceful anoxic species and the domination of the photosynthetic organisms. A record of this time is written in the rocks, where iron oxide is deposited in bands from around this time. Salvation came in the form of bacteria that could detoxify this terrible gas, reducing it back again into DHMO. Soon everyone started carrying around these purification factories and a balance between the destructive plants and the benign animals was restored. | 
