Grade 06 - Chapter 2: Oceans and Continents - Notes

Earth's Surface: 

The Earth’s surface is divided into two main types: land and water. Around 71% of the Earth's surface is covered by water, while land makes up only 29%. 

Land is distributed into large landmasses called continents, and water is mostly found in large bodies called oceans. 

Continents: 

Continents are the large landmasses on Earth. There are seven continents: 

• Asia: The largest continent, home to more than half of the world’s population. 
• Africa: Known for its diverse wildlife, it is the second-largest continent. 
• North America: Includes countries like the USA and Canada. 
• South America: Known for the Amazon Rainforest and Andes Mountains. 
• Antarctica: The coldest continent, covered with ice and uninhabited by humans. 
• Europe: Known for its rich history and culture, Europe is smaller but densely populated. 
• Australia: The smallest continent, often referred to as "the island continent." 

 Continents as Landmasses:

These are continuous expanses of land that are distinct and separate from each other, each with its unique geographical features, climate, and ecosystems. 

 Oceans: 

Oceans are vast bodies of saltwater that cover most of the Earth's surface. There are five oceans: 

• Pacific Ocean: The largest and deepest ocean, located between Asia and the Americas. 
• Atlantic Ocean: The second-largest ocean, separating the Americas from Europe and Africa. 
• Indian Ocean: Located mainly between Africa, Asia, and Australia. 
• Southern Ocean: Surrounds Antarctica and is known for its cold waters. 
• Arctic Ocean: The smallest and shallowest ocean, located around the North Pole. 

 Oceans’ Importance:

Oceans play a critical role in regulating the Earth’s climate, providing food, and supporting marine life. They are also important for trade and transportation. 

 Marine Ecosystems: 

The ocean is divided into different zones based on depth, each home to various species. The sunlight zone (near the surface) supports most marine life, while the deeper zones have creatures adapted to darker, colder environments. 

 Types of Marine Life: 

• Plankton: Tiny organisms that drift in ocean currents and are a vital food source for many marine creatures. 
• Fish: Oceans are home to numerous fish species, ranging from small fish like sardines to large predators like sharks. 
• Marine Mammals: Whales, dolphins, and seals are examples of marine mammals that live in the ocean. 
• Coral Reefs: These are diverse underwater ecosystems, often referred to as the "rainforests of the sea." Corals are tiny animals that build large structures where many marine species find shelter and food. 

 Importance of Ocean Life: 

• Biodiversity: Oceans are rich in biodiversity, housing countless species of plants, animals, and microorganisms. 
• Food Source: Many humans rely on the ocean for seafood, and marine species form a major part of global diets. 
• Oxygen Production: Oceans contribute significantly to the Earth’s oxygen supply through the photosynthesis of marine plants and algae. 
• Climate Regulation: Marine life, particularly plankton, helps regulate carbon dioxide levels, affecting global climate patterns. 

 Threats to Ocean Life: 

• Pollution: Plastic waste, oil spills, and chemical pollutants severely affect marine ecosystems. 
• Overfishing: Excessive fishing depletes fish populations, disrupting the balance of marine life. 
• Climate Change: Rising ocean temperatures and ocean acidification pose a threat to coral reefs and other marine species. 

 Land and Water Distribution: 

The Northern Hemisphere contains more land, while the Southern Hemisphere is dominated by water. Most of the continents are located in the Northern Hemisphere. 

The land and water distribution affects climate, weather patterns, and biodiversity. 

 Ocean Disasters: 

Ocean Disasters include natural events like tsunamis, hurricanes, and storms that originate in or are influenced by the oceans. These disasters can cause significant damage to coastal areas and affect human life. 

• Tsunamis: Huge ocean waves usually caused by underwater earthquakes or volcanic eruptions. 
• Hurricanes/Cyclones: Powerful storms that form over warm ocean waters and can lead to heavy rainfall, flooding, and strong winds. 

 Geographical Features: 

Mountains, valleys, rivers, and plains can be found on continents, while trenches, ridges, and coral reefs are features of the oceans. 

 Plate Tectonics:

The movement of Earth's plates can cause changes in landmasses, create mountains, and lead to earthquakes, which can also trigger ocean disasters like tsunamis. 

 2004 Indian Ocean Tsunami 

When did it happen? 

On the morning of December 26, 2004. 

Where did it happen? 

• The tsunami mainly affected countries around the Indian Ocean, including:India (especially Tamil Nadu and Andaman & Nicobar Islands) 
• Indonesia 
• Sri Lanka 
• Thailand 
• Maldives 
• Bangladesh, Somalia, and other coastal nations 

What caused the tsunami? 

• A powerful undersea earthquake (magnitude 9.1–9.3) struck off the west coast of northern Sumatra (Indonesia). 
• This earthquake happened because of a sudden movement of tectonic plates beneath the ocean. 
• The quake caused the seafloor to rise and displace a huge amount of water, creating massive tsunami waves. 

What is a tsunami? 

• A tsunami is a series of giant sea waves caused by an underwater earthquake, volcanic eruption, or landslide. 
• These waves move very fast and can be extremely destructive when they reach land. 

How powerful was it? 

• The waves reached heights of 10 to 30 meters (as tall as a 10-storey building) in some places. 
• It traveled across the Indian Ocean at speeds up to 800 km/h (as fast as a jet airplane). 

What was the impact? 

• Millions were left homeless. 

• Coastal villages were wiped out. 

• There was huge destruction to homes, schools, and fishing boats. 

Relief & Help 

• Many countries and organizations around the world sent aid, food, and rescue teams. 
• Governments built early warning systems to alert people if a tsunami is likely to happen again. 
• The tsunami occurred a day after Christmas in 2004. 
• It’s one of the largest natural disasters in modern history. 
• It led to the development of the Indian Ocean Tsunami Warning System. 
• Scientists now monitor earthquakes under the sea to reduce the risk of such disasters.