The Cambrian period is one of the most significant geological time periods. Lasting about 53 million years, it marked a dramatic burst of changes in life on Earth known as the Cambrian Explosion. It is from this period that the majority of the history of life on Earth, as documented by fossils, is found. Called the fossil record, the layering of these mineralized imprints of organisms preserved in sedementary rock have allowed geologists to build a historical record of plant and animal life on Earth.

Capillaries are small thin-walled vessels that permit the exchange of oxygen, carbon dioxide, nutrients, and waste between blood and the body's cells. This process of exchange is called diffusion.

The broadest classification of life splits all organisms into three groups called domains. The three domains of life are bacteria, archaea and eukaryota.

The water then accumulates as runoff and eventually returns to bodies of water or is absorbed into the Earth (infiltration) and becomes part of the water table, an underground resevoir of fresh water.

An element in a solid state has atoms or molecules that are constricted and do not move freely. Solids maintain a constant volume and shape and exist at a lower temperature than liquids or gases.