Including us humans, we have to breathe oxygen all the time. We can go without food for seven days and water for three days, but most people can't live for three minutes without breathing!
On June 2nd, 20021year, a paper published in Nature, a top academic journal in Britain, showed that the oxygen content in the oceans and lakes on the earth was declining sharply. Will it continue into the atmosphere in the future, and will life on earth be dangerous?
After the oxygen content in the ocean decreased, the oxygen content in the lake also began to decrease.
Since the end of 20 19, a study involving scientists from 17 countries shows that the oxygen content in the oceans on the earth has been declining for the past 50 years. From 1950s to 20 19, the oxygen content in the ocean decreased by 1%~2%, and it is expected to reach 265438+.
That is, more than 90% of marine life activities, so the continuous decline of oxygen content will have a devastating impact on marine ecology, and rich marine life is one of the main sources of human protein!
Another study shows that lakes and oceans are also facing a sharp drop in oxygen content. Researchers have investigated more than 400 lakes in the United States and Europe, and found that the oxygen content in lakes has also dropped sharply, while the data in the journal Nature shows that the oxygen content in lakes has dropped much more than that in the ocean:
In other words, the oxygen content of lake water is more than twice that of ocean. Scientists' research shows that the main reason for the decrease of oceans and lakes may be related to the increase of temperature and the decrease of transparency caused by water pollution!
Kevin C Ross, a professor of biology at Rensselaer Institute of Technology, said that the factors affecting transparency came from sewage, fertilizers and runoff from cars and power plants. This really means that many fish habitats may become unsuitable for fish in the future.
When the sixth mass extinction happened.
Since the Cambrian explosion of life, the earth has experienced five mass extinctions, namely:
Among them, the extinction event in the late Devonian was caused by the sharp decline of oxygen content, but there are different opinions on why it caused hypoxia. A more reliable opinion is that a large number of plants multiply, leading to an increase in weathering, a large increase in iron entering the ocean, and eutrophication of the water system, leading to a major anoxic event in the ocean!
At present, the reason is that global warming leads to the decrease of dissolved oxygen, and a large number of chemical fertilizers enter the ocean and lead to eutrophication, which seems to have the same effect as the extinction event in the late Devonian!
However, the sixth extinction of life has already begun, even if the great hypoxia event did not occur!
On June 2, 2020, the BBC published a report with a scary title, "The earth is facing the sixth mass extinction, endangering human survival and the continuation of civilization". There is a lot of data that makes people shudder:
Moreover, this speed has exceeded the speed of the prehistoric mass extinction, because the time of mass extinction in those years has been extended to 100 to 10 million years, and this time it is the speed of extinction visible to the naked eye. If it goes extinct at the present rate, it will only take a few hundred years and the earth will become bare. One man's army is the only one!
For example, the spread of buttercup led to the extinction of amphibians in many parts of the world, which is the most typical extinction caused by human activities. 20 18 In May, a paper in Science magazine showed that the spread of Ranunculus ternatus is highly consistent with human global trade activities and has a strong correlation with human activities!
Dodo, homing pigeon and Strada manatee died out earlier, while Platts wild horse, high-nosed antelope and clouded leopard in Taiwan Province are more recent, and even many of them disappeared in the history of the earth before scientists discovered them!
Many other animals are threatened by human beings, such as Ethiopian wolves, Javanese rhinos, parakeets with yellow ears, Ganges crocodiles and California Bay porpoises, and elephants that are almost extinct because of ivory trade.
Further reading: dissolved oxygen
Oxygen is a nonpolar molecule. In fact, it is difficult to dissolve in polar water molecules, so it only dissolves rather than reacts, or oxygen molecules are "embedded" in the gaps of water molecules. This "solubility" is related to many factors, such as increasing the contact area between water and air, or lowering the temperature, such as:
Under a standard atmospheric pressure, a liter of water can only dissolve about 9 mg of oxygen, which is about 1/35 of the oxygen content in the air. Only 6.9 mg oxygen can be dissolved at 35, and 14.6 mg oxygen can be dissolved at 0.
Oxygen in water is the source of oxygen exchange for fish. The minimum oxygen demand of most fish is 1mg/L, which seems to be much higher than the dissolved oxygen at room temperature. However, due to the concentration of local fish, the oxygen content will drop sharply, which is also related to the impurities in the water and the air pressure at that time. So before the thunderstorm, the air pressure drops and the fish will float.