Early explorers were often driven by curiosity and a need for territory. They wanted to know about other people, if they were stronger than themselves, or would they make good partners in trade?
There was also a curiosity about the ocean. In the 1400s many men believed that the world was flat. As they looked at the horizon, it looked as if the world ended somewhere over the sea. As these people surveyed the setting of the sun every day, it appeared that the ocean swallowed the sun each evening. Plus there was also fear that there would be sea monsters that would devour any that would invade their territory. Then some explorers decided to take it upon themselves to face the unknown and travel to the horizon on the vast ocean. They discovered that the sea was not the end of the earth, and that the sea was a place to be respected, not because of the monsters, but because of the vastness and the relentless storms that could be faced. Plus no matter how far west they traveled the setting sun still set further west.
There was also a considerable wonder as to what was under the sea, and how deep the water truly was. This was a puzzle that remained until technology developed the correct instruments that allowed these early oceanographers to go beneath the surface. When they did explore they saw such beauty. Fish of all types and sizes and plants that could grow, even in limited life and so much more. These excursions led to even more questions such as: Is it possible to reach the bottom of the ocean? How would underwater life differ as this exploration continued? When the H.M.S. Challenger set off to examine this still strange world, they were able to answer many questions and help fellow scientists think up many more. They were able to discover the depth of the ocean, by measuring in various areas. They also were able to discover that, even at depths where there was no visible light, there was still life. This life was vibrant with colors and had adaptations which allowed them to see in the darkness.
As time continues, people still turn to the oceans to discover the history of the earth, as some of this history from the surface has been eroded away, they look at tides and currents to answer questions on weather and climates. There are even those that look to the ocean to find treasure, either that was thrown over board a ship or on a sunken ship.
At times the ocean has been called one of the final frontiers, this is because the more we discover from it, the more there seems to be to learn.