Water and the dinosaurs

Water continually cycles among the oceans, atmosphere, land, and underground reservoirs, so water is reused through organisms and bodies of water. A cautious inference follows: a glass of water today could contain molecules that were once part of a dinosaur, but this cannot be established for any particular glass. Nor can Earth’s water inventory be said without qualification to be “exactly the same as during planetary formation”: its origin, exchange with the interior, and changes over geological time remain under study. [1–4]