Sea water is the salty water found in oceans and seas, covering more than 70% of the Earth's surface. It is a complex mixture of water, dissolved salts, organic materials, and gases. Here are some key characteristics of sea water:

1. **Salinity**: Sea water has a high salt content, averaging about 35 grams of dissolved salts per liter. This salinity is mainly due to the presence of sodium chloride (table salt), along with other salts like magnesium, calcium, and potassium.

2. **Color**: The color of sea water can vary from deep blue to green, depending on factors such as depth, sunlight, and the presence of algae or other organisms. It often appears blue because water absorbs colors in the red part of the light spectrum and reflects and scatters blue light.

3. **Temperature**: Sea water temperatures vary widely depending on location, depth, and season. Surface temperatures can range from just above freezing in polar regions to over 30°C (86°F) in tropical areas.

4. **Density**: Sea water is denser than fresh water due to its salt content. This higher density affects ocean currents and marine life buoyancy.

5. **pH**: The pH of sea water is typically around 8.1, making it slightly alkaline. However, ocean acidification caused by increased CO2 levels is gradually lowering this pH.

6. **Marine Life**: Sea water is home to a vast array of marine life, from tiny plankton to large whales. Its nutrients support complex ecosystems and food chains.

Sea water plays a crucial role in regulating the Earth's climate, supporting marine ecosystems, and providing resources and recreation for humans.