Just 2.3 billion years ago, the air surrounding the Earth was completely oxygen free. For the then primitive forms of life, this circumstance was a present.
Unicellular bacteria that lived in the primeval ocean did not need oxygen to maintain their vital functions. Then something happened.
How did oxygen appear on earth?
Scientists believe that with the development of some bacteria "learned" to extract hydrogen from water. It is known that water is a combination of hydrogen and oxygen, therefore the by-product of the hydrogen extraction reaction was the formation of oxygen, its evolution into water, and then into the atmosphere.
Some organisms have adapted over time to live in the atmosphere with new gas. The body has found a way to curb the destructive energy of oxygen and use it for the controlled breakdown of nutrients, during which the energy used by the body to maintain its vital activity is released.
This method of applying oxygen is called breathing, which we use daily, and sow the day. Breathing is a way to divert the oxygen threat from itself: it has made possible the development on Earth of larger organisms - multicellular, already complex in structure. In the end, it was thanks to the appearance of breathing that evolution gave birth to man.
Where did oxygen come from on earth?
Over millions of years, the amount of oxygen on earth has increased from 0.2 percent to the current 21 percent of the atmosphere. But not only the bacteria of the oceans are to blame for the increase in oxygen in the air. Scientists believe that the colliding continents were another source of oxygen. In their opinion, during the collision, and then with the subsequent divergence of the continents, large quantities of oxygen were released into the atmosphere.
How? As a result of collisions and divergences of the continents, huge sedimentary rocks descended to the seabed, entraining a large amount of organic matter. If this did not happen, then oxygen would be spent more on the digestion and oxidation of these organic substances. Since they became inaccessible to oxidation, a peculiar saving of oxygen occurred, and its volume in the atmosphere became larger.
Escape from oxygen
Some organisms managed to adapt and even benefit from the presence of oxygen in the atmosphere. However, most organisms did not tolerate changes in living conditions and became extinct. Some species of living things were saved by hiding from oxygen in deep gaps and other secluded places. Many still live happily in the roots of legumes, capture gaseous nitrogen from the atmosphere and use it for the synthesis of amino acids (building blocks of protein) of plants.
The botulism bacterium is another fugitive from oxygen. It is found in meat, fish, plants. If during the preparation, the botulism stick is not destroyed by the high temperature during cooking, then it can then multiply intensively in canned food, which are prepared from the above products.
This is because there is no air access to the cans. If you eat foods infected with botulism sticks, you can be dangerously sick.
