Covering nearly three-quarters of the Earth's surface, water is the source of all life on our planet. Water-borne transportation has allowed exploration of much of the globe and facilitated the rise and fall of great empires. Beneath the surface of our oceans, lakes, rivers, and wetlands lies a physical record of humankind preserved in prehistoric and historic shorelines, shipwrecks, inundated cities, harbor works, and other traces of our past.

Archaeology is the scientific study of the human past through investigation of artifacts (the physical remains of cultures), structures, the use of animals and plants, and human remains. Its goal is greater knowledge about past human culture and behavior. Underwater archaeology carries these studies into a specialized environment, one containing numerous challenges and rewards for archaeological investigators.

The majority of underwater archaeologists specialize in the study of nautical archaeology: the study of ships, shipping, and the construction and operation of all types of prehistoric and historic watercraft. For these specialists, shipwrecks are the focus of research, many of which (but by no means all) may be found underwater.

Other types of sites in the underwater archaeologists' domain include: ancient land sites inundated after the last ice age; sinkholes or bogs where people placed offerings or buried their dead; cities and harbors now submerged from sea level change or earthquake; and dwelling, agricultural, and industrial sites along rivers, bays, and lakes. Underwater archaeologists make extensive use of historical records such as ships' plans, logs, and manifests; explorer's accounts; old maps; and legal, business, and tax records. They also study long-term geologic changes to locate submerged early man sites.

Putting it All Together
The practice of underwater archaeology is truly interdisciplinary, combining the methods of various allied fields of study including anthropology, chemistry, ethnography, geology, history, naval architecture, oceanography, and paleography -- to name only a few.

Although much underwater archaeology is conducted with standard scuba equipment, using simple measuring, mapping, and drawing techniques, archaeologists have borrowed special methods for working in the underwater environment from marine science as well as commercial and military diving. Technologically sophisticated projects use both acoustic and magnetic remote-sensing equipmbpent for detecting underwater archaeological sites, and acoustic, optical, infrared, and robotic methods for pinpointing, mapping, and documenting sites.

Archaeological Conservation
Underwater archaeology does not always involve excavation, but when material is removed for detailed study, laboratory facilities available to preserve the artifacts are essential. The miraculously well-preserved condition of objects is more apparent than real.

Photos courtesy Projecto HMS Swift and Ships of Discovery

During lengthy immersion, artifacts react chemically with the water and sediments surrounding them.. Sudden removal from their watery environment and exposure to air can set off a chain of chemical and physical reactions in the objects that can lead to their destruction.

Conservators are specialists who work with archaeologists to preserve artifacts for study and display. The conservation of objects takes much longer than their actual excavation, and the long-term care of a collection of excavated objects is expensive and time-consuming. Unless proper facilities and resources are available, it is often best to leave objects in their underwater environment. Conservators also work with archaeologists and site managers to monitor the condition of sites and artifacts left in place to preserve them for future generations.