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It includes the ground you walk on and the ocean floor. crystal: One grain of a mineral that may have a regular shape and smooth sides. element: A substance made of only one kind of atom. field guide: A book with facts and pictures that is used to identify different kinds of animals, plants, rocks, shells, and other things in nature. fossil: Imprints made by ancient plants or animals, or preserved parts of plants and animals. An index fossil appears in only a few layers of rock. These help scientists figure out the age of similar rock layers far away.

What does this have to do with office buildings? Limestone is often used to build offices, banks, and other public buildings. Next time you’re in the library, check out the walls and floors. You just might see a fossil! gs! r Rubbin u o Y t e rg Don’t Fo ntown llect “dow co bings of You can aking rub paper off m y b ” s fossil l the easy! Pee Hold them. It’s red wax crayon. lo e a dark-co in paper over th n th f yo o ra e c c e th a pie e side of paper in th b u R . fossil r the forth ove e back and n until you see th ate o d ti e c e th ir d te one il.

Your body stores minerals too. You get the minerals you need from the food you eat. Milk and cheese contain calcium, which hardens your teeth and bones. Meat and some vegetables contain iron, which helps your blood cells make hemoglobin, a substance needed to carry oxygen to other cells. Your nerves need sodium to do their job. You can get it from salt. You also need potassium, iodine, and zinc to help keep you healthy. Hot chocolate has calcium and iron. Beef is high in iron. Bananas have a high potassium content.