Calcium is even more plentiful on Earth than magnesium. The silvery, semi-soft metal easily forms compounds with both oxygen molecules and water. In nature it is typically found as calcium carbonate, or limestone. Calcium is a key component in the structures of living things including bones, teeth, shells and exoskeletons. Calcium is also an important substance for manmade structures because it is used to make plaster, cement, drywall and other building materials.

Shiny and soft, strontium forms compounds with oxygen and other oxides such as carbonate (CO₃), nitrate (NO₃), sulfate (SO₄) and chlorate (ClO₃). Salts derived from strontium compounds burn red and are used in fireworks and signal flares.

Unlike the transparency of beryllium, X-rays cannot penetrate barium. Barium sulfate is commonly used to aid in using X-rays to detect problems in the digestive tract. This compound is insoluble in water and coats the esophagus, stomach and intestines when swallowed. Barium nitrate and barium chlorate are used in fireworks to give off green light when heated. Barium is also an ingredient in paint pigments.

Radium is white in color and soft and shiny like the other alkaline earth metals. However, its radioactivity sets it apart from the rest of its group. Soon after its discovery by the Curies in the late 1800s, radium was used for medical therapies and to make glow-in-the-dark clocks and watches. Decades later the use of radium ceased when people discovered the dangers of radiation. Today radium is used in the treatment of certain types of cancers.