Ever since human beings looked out to the sea, they have wondered what was out there. We first began to dive for food. The first sailing vessels made the world smaller and brought together many cultures that had previously remained isolated. The first crude diving bells allowed us to work underwater for extended periods of time. As ship construction techniques continued to advance, we were able to venture farther out to sea. New lands were discovered, and the world was revealed to be round. Advances in diving technology led to diving suits and the first submarines. As we began to dive deeper into the sea, we began to understand how deep the oceans really were. And in spite of the high pressures and cold temperatures, life flourished in the depths. As we mapped the ocean floor, the complexity of this alien world became apparent. The discovery of hydrothermal vents stunned the scientific community when an entire ecosystem of life was discovered that needed no sunlight to survive. In this section of Sea and Sky, you can explore these major milestones and discoveries and learn about the history of ocean exploration. Click here for a list of credits and sources.