Which element is the most abundant?

The most abundant element depends on where you look. In the universe as a whole, hydrogen dominates, accounting for roughly 75 percent of all ordinary (baryonic) matter by mass, followed by helium at about 24 percent; together these two lightest elements make up almost everything, since they formed in the first minutes after the Big Bang. On Earth, the picture is very different. Oxygen is the most abundant element in the Earth crust, making up about 46 percent by mass, largely locked up in rocks and minerals combined with silicon, the second most abundant. In the human body, oxygen is again the most abundant element by mass, mostly because our bodies are largely water. So while hydrogen rules the cosmos, oxygen dominates our planet solid crust and our own bodies.