It's in your body, the food you eat and the beverages you drink.
All forms of life need it, and if they don't get enough of it, they die. In some places, it's treasured and incredibly difficult to get.
In others, it's incredibly easy to get and then squandered.
Atoms of each element contain a characteristic number of protons.
Over the centuries, our view of light has changed dramatically.
A popular way to determine the ages of biological substances no more than 50,000 years old is to measure the decay of carbon-14 into nitrogen-14.