Seashells are formed out of the calcium-rich outer mantle tissue of mollusks and certain other marine animals. The shells are made almost entirely from calcium carbonate excreted over a protein network generated by the top layer of the animal's body.
Creatures that create seashells are not the only animals that protect themselves with hard exterior body parts. For example, turtles and tortoises also make shells composed mostly of calcium. However, their structure is dramatically different.
Seashells are exoskeletal structures devoid of living cells. Turtle shells are more intimately connected to the turtle and contain blood vessels and other living material, including bones. The shells also contain nerves, while seashells do not.
Mollusks and other shell-bearing marine animals develop shells soon after birth. As they grow, they enlarge their shells by secreting additional protein around the sides of the shell and covering that network with calcium carbonate. This is a gradual and continuous process. Turtle shells also grow gradually, but without chemical secretions. These shells are part of the turtle's skeleton and grow proportionally with its other bones.
When mollusks die, their soft bodies decompose. Their shells, however, remain intact for a long time. These empty shells are often appropriated by hermit crabs, which use them as a temporary home. Once a hermit crab grows too large for a shell, it discards it and searches for a new one.Learn More
Seashells, which are the exoskeletons of mollusks such as snails, clams and oysters, form from the bottom up starting with mantle tissue located underneath and in contact with the shell. The mantle secretes proteins and minerals to form layers. Mollusk shells have three separate layers: the uncalcified outer layer called the proteinaceous periosteum, a calcified prismatic layer and a calcified inner layer called nacre.Full Answer >
Mountains are formed by the movements of the Earth's crust and tectonic plates. Movements deep beneath the Earth's surface cause a variety of reactions, which results in different types of mountains. Mountains can form as a result of volcanic activity, the collision of two tectonic plates or movement along a fault line.Full Answer >
Onyx is a type of agate known as chalcedony, formed by intergrowths of silica minerals. The chert form of quartz is also used to make onyx jewelry items.Full Answer >
Visible light is created when electrons that are located inside atoms return to their ground state after being in an excited state, according to the University of Hartford. Light is radiant energy, meaning it is electromagnetic radiation that can be seen with the human eye.Full Answer >