Science Background

Pensacola Barrier Islands
The sediment that reaches our beaches comes from a very small drainage area. In fact, virtually all the particles are from erosion of the southernmost portion of the Appalachian Mountains. The fast moving streams bring mostly grains of clear white quartz the short distance across the coastal plain to the Gulf. The westward longshore current deposits it as pure white sand along the coast and barrier islands of the seashore. Seashells contribute to the white sand of the west coast of Florida, but their sand isn't as white as Pensacola beaches. (See http://www.nps.gov/archive/guis/extended/MIS/MNature/Geology.htm).

Physics of erosion
Much of weathering and erosion is related to physical concepts. For example, the amount of rock that weathers in a sand storm is related to the mass of the sand and the speed with which it hits the rock. The size of particles that a stream can carry is related to speed of the stream. The energy of the stream comes from the conversion of its potential energy from being on a mountain to kinetic energy.

Karst topography
Limestone is easily dissolved by acids produced by organic matter. In some places the limestone is covered by sandstone or other harder, less dissolvable rock. If water, particularly acidic water, can get through the upper stone layer, it can dissolve and erode the limestone. This process can result in the formation of caves. If the upper rock is thin, the roof of the cave can cave in, resulting in a sinkhole. Florida has a lot of limestone which has resulted in many sinkholes in the state, though they are not so common in northwest Florida.

In January 2007 Sac Actun, an underwater cave in the Yucatan Peninsula, was determined as the longest underwater cave system in the world (95 miles). In June, nearby Ox Bel Ha was measured as longer (102 miles). Mammoth Caves in Kentucky is the world's longest cave system, with 365 miles explored.

Chalk and limestone
In this experiment we use chalk instead of limestone. Both are calcium carbonate. (Some chalk is now gypsum, hydradated calcium sulfate.) Calcium carbonate is the main component of seashells, snails, and eggshells. It is common as an antacid and in some toothpastes. Calcium carbonate reacts with vinegar to create carbon dioxide (the bubbles you see) and calcium acetate. The calcium carbonate that becomes limestone is created by single cell organisms that take up calcium from sea water to create calcium carbonate shells. When they die or discard their shells, the shells fall to the sea floor. Over time they are compacted to become limestone.

One type of creature that makes calcium carbonate shells is the coccolithophores, a type of single celled organism. An image of one shows the calcium carbonate plates. They are visible in satellite images as bright aquamarine patches (Bering sea, Ireland). Another good image is in the November 2007 National Geographic in Where in the World?

Basic procedure
Key Knowledge
Science Background
Script Idea
Barrier Islands
Alternate Ideas
Printable Version of this Information