An inland sea is a shallow sea

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

 that covers central areas of continents during periods of high sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 that result in marine transgression

Transgression (geology)

A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water...

s. In modern times, continents stand high, eustatic sea levels are low, and there are few inland seas, none larger than the Caspian Sea

Caspian Sea

The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

. Modern examples might also include the recently (less than 10,000 years ago) reflooded Persian Gulf

Persian Gulf

The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...

, and the South China Sea

South China Sea

The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...

 that presently covers the Sunda Shelf

Sunda Shelf

Geologically, the Sunda Shelf is a south east extension of the continental shelf of Southeast Asia. Major landmasses on the shelf include the Malay Peninsula, Sumatra, Borneo, Java, Madura, Bali and their surrounding smaller islands. It covers an area of approximately 1.85 million km2...

.

At various times in the geologic past, inland seas have been greater in extent and more common than at present.

• A vast inland sea extended from the Gulf of Mexico
  Gulf of Mexico
  The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
  
   deep into present-day Canada
  Canada
  Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
  
   during the Cretaceous. See the Western Interior Seaway
  Western Interior Seaway
  The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
  
  .
• At the same time, much of the low plains of modern-day northern France and northern Germany were inundated by an inland sea, where the chalk was deposited that gave the Cretaceous
  Cretaceous
  The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
  
   Period its name.
• The Amazon
  Amazon River
  The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
  
  , originally emptying into the Pacific, as South America rifted from Africa, found its exit blocked by the rise of the Andes about 15 mya. A great inland sea developed, at times draining north through what is now Venezuela before finding its present eastward outlet into the South Atlantic. Gradually this inland sea became a vast freshwater lake and wetlands where sediment flattened its profiles and the marine inhabitants adapted to life in freshwater. Over 20 species of stingray
  Stingray
  The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
  
  , most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon, which is also home to a freshwater dolphin
  Dolphin
  Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
  
  . In 2005 fossilized remains of a giant crocodilian, estimated to have been 46 ft (14m) in length, were discovered in the northern rainforest of Amazonian Peru
  Peru
  Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
  
   http://www.dailytimes.com.pk/default.asp?page=story_12-9-2005_pg6_6.
• In Australia
  Australia
  Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
  
   the promise of an inland sea is often said to have been one of the prime motives of inland exploration during the 1820s and 1830s. Although this theory was championed by the explorer Charles Sturt
  Charles Sturt
  Captain Charles Napier Sturt was an English explorer of Australia, and part of the European Exploration of Australia. He led several expeditions into the interior of the continent, starting from both Sydney and later from Adelaide. His expeditions traced several of the westward-flowing rivers,...
  
  , it enjoyed little support among the other explorers, most of whom were more inclined to believe in the existence of a Great River which discharged into the ocean in the north-west corner of the continent.
• The Baltic Sea
  Baltic Sea
  The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
  
   is a brackish
  Brackish water
  Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
  
   inland sea, arguably the largest body of brackish water in the world (other possibilities include the White Sea
  White Sea
  The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...
  
  ). It occupies a basin formed by glacial erosion.

External links

Geology Project - Inland Sea Movement Through Time