Origin and Distribution of Earth's Water

Origin of the Oceans

• Scientists believe Earth's water came from either a distant source (like comets or meteorites) or a local source (like volcanoes), or a combination of both.
• Comets and meteorites are possible distant sources of Earth's water.
• Volcanic activity released large amounts of water vapor and other gases into the early atmosphere. This water vapor eventually condensed to form the oceans.

Distribution of Earth's Water

• The oceans hold about 97% of Earth's water.
• Fresh water makes up the remaining 3% and is found in ice caps (Greenland and Antarctica), rivers, lakes, and underground sources.
• The northern hemisphere has slightly more water than land.
• In contrast, the southern hemisphere is almost entirely covered by water.

Sea Level

• Sea level changes over time, affected by melting ice (during warm periods) or expanding glaciers (during ice ages).
• Tectonic forces also influence sea level by lifting or lowering portions of the Earth's crust.
• Scientists link rising sea levels to melting glaciers due to global warming.

Ocean and Atmosphere Interaction

• Oceans release atmospheric oxygen.
• Oceans act as a large reservoir of carbon dioxide.
• Oceans influence large-scale atmospheric moisture and heat circulation patterns.

Chemical Composition of Seawater

• Salinity measures the amount of dissolved salts in seawater.
• Seawater is denser than freshwater, and its density increases with salinity.
• Estuaries are areas with lower salinity, often where rivers meet the ocean.

Ocean Movements: Waves

• Waves are rhythmic movements that carry energy through water.
• Wind blowing over the ocean's surface creates waves.
• The highest point of a wave is the crest, and the lowest point is the trough.
• Waves become breakers when their height increases, and length decreases as they approach the shore.

Ocean Movements: Tides

• Tides are the periodic rise and fall of sea levels.
• High tide is the highest point of water rise.
• Low tide is the lowest point of water fall.
• The gravitational pull of the Sun and Moon affects the tides.

Ocean Movements: Influence of Tides

• Lunar tides are significantly stronger than solar tides due to the Moon's proximity to Earth.
• Spring tides occur when the Sun, Moon, and Earth are aligned, resulting in higher high tides and lower low tides.
• Neap tides happen when the Sun, Moon, and Earth form a right angle, causing lower high tides and higher low tides.

Ocean Movements: Currents

• Surface currents are wind-driven water movements primarily affecting the top few hundred meters of the ocean.
• These currents follow predictable patterns driven by global wind systems.
• Gyres are closed current circuits influenced by continents. Currents are deflected either north or south by land masses.

Ocean Movements: Upwelling

• Upwelling is the upward movement of ocean water.
• Upwelling occurs when surface water is moved offshore, causing deeper, colder water to rise to the surface to replace it.