Sentence:  Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert <WSD>water</WSD> and carbon dioxide into carbohydrates and waste oxygen using solar energy. 
Meaning of the word marked with <WSD> tags:  (Q283) A substance (of molecular formula H₂O) found at room temperature and pressure as a clear liquid; it is present naturally as rain, and found in rivers, lakes and seas; its solid form is ice and its gaseous form is steam.