There are mainly 5- oceans on the earth, they are called the Atlantic ocean, Pacific ocean, Indian ocean, Arctic ocean and southern oceans. All these oceans flow into each other.There are oceans currents, they travel between them. There is thermohaline ciculation , which sometimes takes thousand sof years to complete one circulation. So in this sense we can call it one large ocean in the world. This fact was true probably 250 million years ago. The world was covered in a single large ocean. This is because the 71 percent earth is covered with water. The scientists has discovered more than 230,000 marine living creatures, and they think this is ten time more which is not dicovered.

There are also further subdivision of oceans, the Antartic ocean is considered as the extension of the Indian ocean, pacific ocean and Atlantic ocean. Arctic ocean is also considered the sea of the Atlantic ocean, the smaller portion of the oceans are called, the sea, bays, gulfs and straits. The caspian Sea, it has not out flow, its suface area is 371,000km2. It is bounded by northern Iran. There are 130 rivers which provide inflow to the Caspian sea.

The Black sea, it is bounded to Europe and Anatolia, it is inland sea like the Caspian sea. It has area 436,400km2, its maximum depth is 2206m. It joins the global ocean system. The Mediterranean sea, it is connected to the Atlantic ocean, it is bounded by the land of Europe and Anatolia. It is only 14km wide. Its depth is 1500m. Now the question arises, how many oceans are there, we can say there are five oceans or there is one ocean that is The World Ocean , or the Global Ocean. Because the all oceans are interconected with the continuos circulation.

The physical properties of the oceans are, the area of the world oceans is 361×10⁶ km² and its volume is 1.3 billion cubic kilometers. Its average depth is 3790m and maximum depth is 10923m. The expese of the oceans covers the 66 percent of the earth surface. The total mass of the oceans is 1.4×10²¹ kg, that is 0.023 percent of the earth mass. The oceans water looks blue, the reason is the natural color of water is slightly blue, when we see the water in large volume, it is looked clear blue. The deepest point of the oceans is located in the Pcific ocean.