1. The Oceans Physical Oceanography

2. Modern Oceanography Challenger expedition investigated ocean currents, water temperature, chemical composition, seafloor, and topography Used nets, bottom dredges, and other tools Later expeditions (such as the ship Meteor) used sonar for the first time

3. Where are we now? Satellites: monitor temperature, currents, and wave conditions Submersibles (underwater vessels): investigate deep ocean trenches Seafloor has been mapped out using side-scan sonar: technique directs sound waves to seafloor at angle

4. Origin of the Oceans Has Earth always had oceans? Radioactive studies show and lava flows offer evidence that water has been abundant throughout Earth’s history Where did the water come from? 1)Comets that occasionally collide with Earth 2)Volcanism: allow water to rise from deep in Earth’s interior

5. Volcanism Gases emitted from volcanic eruptions contain water vapor At one point, episode of massive violent volcanism that released large amounts of water vapor and other gases. As crust cooled, eventually condensed into the oceans Water still being added to hydrosphere by volcanism

6. Distribution of Earth’s Water Oceans contain 97% of water on Earth Sea Level: level of the ocean’s surfaces; rises and falls in response to melting ice caps and during ice ages All oceans are all interconnected as one body of water