Marine life

Many things live in the sea.

Some are big like whales. Some are too small to see.

They live in salt water. This salt comes from rocks on land.

Tiny things in the water make the air we breathe. This helps our whole world. The ocean is a very big home. Do you like the ocean?

The ocean is a massive home for life. It covers 71 percent of our world. By volume, the ocean provides 90 percent of all living space on Earth.

Marine life includes many different kinds of living things. Some are huge, like the blue whale. Others are tiny microbes. These are organisms so small you cannot see them with your eyes.

Most marine life is made of these tiny parts.

Living things in the sea have different roles. Some are autotrophs. These are makers that use sunlight to grow. They include algae and seagrass. Other life forms are heterotrophs. These must eat other things to get power.

Life in the ocean has a very old story. The first life forms lived in the deep sea. They lived near hydrothermal vents. These are openings in the ocean floor. Over a long time, life changed and grew. Some life even moved from the sea to the land. This helped new worlds grow on shore.

The ocean is a massive home for all kinds of living things. This is called marine life. It includes everything from tiny microbes to the huge blue whale. By volume, the ocean provides about 90 percent of all living space on Earth.

Most of this space is filled with microscopic organisms. These are so small you cannot see them with your eyes. Scientists have found more than 242,000 different species in the sea. They think there might be two million more species waiting to be found. Researchers describe about 2,300 new species every single year.

Living things in the sea have special jobs to do. Some are called autotrophs, which are the makers. These organisms use sunlight or energy from chemicals to grow. Examples include cyanobacteria, algae, and seagrass. Others are called heterotrophs, which are the eaters. These living things must eat other organisms to get energy. This group includes animals, fungi, and many protists. Some fish even travel long distances between different regions. These migratory species help move energy through the ocean. Some organisms, like corals, even help build new land by making reefs.

Life in the ocean has a very long history. The earliest life forms lived in the deep sea. They lived near hydrothermal vents in the Archean oceans. These were tiny organisms called prokaryotes. Later, a big change called the Great Oxygenation Event happened. This changed the chemistry of the water. It led to the rise of eukaryotes, which are more complex cells.

Eventually, the Cambrian Explosion occurred. This was a time when many moving animals became common. Some life even moved from the sea to the land. This helped new ecosystems grow on the shores.

Water is the most important part of this world. It is often called the solvent of life. Most of the water on Earth is salty. About 97.5 percent of all water is saline. The average ocean has about 3.5 percent salt. This salt mostly comes from rocks on land.

Most of our water is in the oceans. The deepest part is the Challenger Deep in the Mariana Trench. It is located in the Pacific Ocean. The oceans also help control the weather on Earth. They act like a large heat reservoir for the planet.

We can even look for life in space. Scientists think moons like Europa might have oceans. Europa is a moon that orbits Jupiter. It may have a large saltwater ocean under its ice. This ocean could be twice as big as Earth's ocean.

Another moon called Enceladus also has an underground ocean. It even vents warm water from its surface. Studying marine life helps us understand our own world. It also helps us wonder about life on other planets.

Marine life, also called sea or ocean life, includes all organisms living in salt water. This encompasses animals, plants, algae, fungi, protists, and single-celled microorganisms. It also includes associated viruses within saline habitats. These habitats range from the vast oceans to coastal lagoons and estuaries.

Marine life is incredibly diverse and vast. Scientists have documented over 242,000 marine species so far. However, they estimate that two million species may still be undiscovered. On average, researchers describe about 2,300 new species every year. By volume, the oceans provide about 90% of the living space on Earth. This makes the ocean a vital sanctuary for life throughout geological history.

Organisms in the ocean are categorized by how they obtain energy. These roles are known as autotrophs and heterotrophs. Autotrophs are the "producers" of the ecosystem. They include photosynthetic organisms like cyanobacteria, algae, and seagrass. These organisms use sunlight to create energy. Some rare autotrophs are chemoautotrophs. They use energy from chemical oxidation to convert inorganic molecules into organic compounds.

Heterotrophs are the "consumers" that must eat other organisms to survive. This group includes all animals, fungi, and many protists. Marine animals are often divided into vertebrates and invertebrates. Vertebrates include fish, marine mammals, reptiles, and seabirds. Invertebrates include everything else, such as many mollusks and crustaceans.

Marine life plays a critical role in regulating the planet. Primary producers like chloroplastic algae and cyanobacteria perform photosynthesis. This process produces oxygen and sequesters carbon. This activity significantly influences the chemistry of the atmosphere. Other species, like migratory fish, move energy between different global regions. These are often called keystone species because they are vital to their ecosystems. Some organisms even shape the physical world. For example, corals build reefs that can create new land through accumulation.

The history of marine life began billions of years ago. The earliest life forms were anaerobic prokaryotes. These were simple cells like archaea and bacteria. They lived in the Archean oceans near deep-sea hydrothermal vents. Later, the Great Oxygenation Event changed marine chemistry. This event likely caused many anaerobes to go extinct. However, it also allowed eukaryotes to evolve through symbiogenesis. This is a process where surviving organisms live together in a cooperative way.

Complex life eventually emerged during the Neoproterozoic era. This led to the Avalon Explosion of sessile macrofaunae. Later, the Cambrian Explosion saw a rise in actively moving animals. These marine organisms eventually moved into fresh waters, helping terrestrial ecosystems develop.

Water is the fundamental requirement for all marine life. It is often called the "universal solvent" because it dissolves many substances. The Earth's hydrosphere includes oceans, lakes, and even underground waters. The world ocean covers 71% of the Earth's surface. It has a mean depth of about 3,700 meters.

The total mass of the world ocean is 1.35 metric tons. This is about 1/4400 of the Earth's total mass. Most of the water on Earth is saline. About 97.5% of Earth's water is salt water. The average salinity is about 3.5% salt per kilogram. Most of this salt comes from the weathering of rocks on land.

Understanding the ocean also helps us search for life in space. Some moons in our solar system may have marine environments. Europa, a moon of Jupiter, likely has a large saltwater ocean. This ocean exists beneath a thick crust of solid ice. It is estimated that Europa's ocean could be twice the volume of Earth's. If hydrothermal vents are active there, it might support multicellular microorganisms. Saturn's moon, Enceladus, also appears to have an underground ocean. This moon actively vents warm water from its surface. These discoveries show how important water is for potential life.

Scientists study these complex systems through marine biology and biological oceanography. They use many tools to understand how life interacts with the physical sea. They look at everything from microscopic phytoplankton to massive blue whales. Phytoplankton can be as small as 0.02 micrometers. In contrast, large cetaceans reach incredible lengths. By studying the connections between species and their environment, we learn how the ocean protects our shorelines and regulates our climate. The ocean acts as a massive heat reservoir for the entire planet.