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More than 99 percent of all species, amounting to over five billion species, [7] that ever lived on Earth are estimated to be extinct. [8] [9] Estimates on the number of Earth's current species range from 10 million to 14 million, [10] of which about 1.2 million have been documented and over 86 percent have not yet been described. [11]
The most notable effects of eutrophication are vegetal blooms, sometimes toxic, loss of biodiversity and anoxia, which can lead to the massive death of aquatic organisms. [8] Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce.
Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply [1] [2] and 90% of habitable space on Earth. [3] Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. [4]
Eutrophication is a common phenomenon in coastal waters, where nitrogenous sources are the main culprit. [21] In coastal waters, nitrogen is commonly the key limiting nutrient of marine waters (unlike the freshwater systems where phosphorus is often the limiting nutrient).
In the absence of a magnetic field, charged particles from the Sun will deplete the atmosphere and further increase the Earth's temperature to an average of around 420 K (147 °C, 296 °F) in 2.8 billion years, causing the last remaining life on Earth to die out. This is the most extreme instance of a climate-caused extinction event.
Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients.It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. [1]
Fish can endure short periods of reduced oxygen. Depleted oxygen levels are the most common cause of fish kills. Oxygen levels normally fluctuate even over the course of a day and are affected by weather, temperature, the amount of sunlight available, and the amount of living and dead plant and animal matter in the water. [8]
A rock, seen at low tide, exhibiting typical intertidal zonation. A specimen of the shell Pinna nobilis exposed by low tide. Because intertidal organisms endure regular periods of immersion and emersion, they essentially live both underwater and on land and must be adapted to a large range of climatic conditions.