How has the amount of water on Earth changed over the last billion years?

global warming, mass heating

Explanation:

is this a psat question, if so do not cheat try your best.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products