First of all, on the issue of depth, documentaries have reported from the sea to the Mariana Trench, so the deepest part must be the Mariana Trench, which is more than 10,000 meters deep. But the Mariana Trench is not the focus of the documentary's description. The documentary focuses on two environments: one is the seabed more than 1,000 meters deep, and the other is a mid-ocean ridge that is 2,000 to 3,000 meters deep.
The film not only introduces the appearance of the creatures in these environments, but also some functions that the creatures have evolved to adapt to the environment. But actually for me, my biggest concern is how creatures survive in these two environments. 1. For the first creature to live on the seabed more than 1,000 meters deep, the principle of "big fish eats small fish" still holds true, but what "small fish" eat is something worth studying. One thing for sure is that there are no plants here - the depth of more than 1,000 meters under water cannot penetrate, and there is no way to carry out photosynthesis. It is also mentioned in the documentary that "marine snow" ( marine snow ) is one of the important ways for creatures to obtain energy here. The "snowflakes" that continue to fall from the upper water body are mainly organic debris, and these organic materials include animal carcasses, phytoplankton, protists, and some animal excrement. With the help of mucus secreted by plankton and bacteria, these small particles slowly clump together and become larger and larger, and over a period of weeks, can grow to a diameter of several centimeters until they fall to the seabed.
If there are large biological remains that can sink, the creatures living near the seabed are even more excited, such as the sperm whale carcass that sank to the bottom of the sea. This phenomenon is called whale fall . When the whale carcass sinks to the seabed, it attracts a type of shark first. When these sharks, who have been hungry for almost a year, bite at the remains of sperm whales, the smell of blood will attract more sharks. At the same time, some small predators will also gather, and soon a natural biological gathering will form around the sperm whale remains.
There is one thing worth thinking about here. On the seabed where the density of organisms in the deep sea is very small, such a dense collection of organisms has gathered in a short period of time. Many organisms must have come from far away. So how did these creatures have such keen senses? When I was collecting data, I found a deep-sea "Telescopefish ( Telescopefish )". The fish is about 15 centimeters long and has tubular eyes that resemble telescopes. So it is conceivable that this kind of physical feature can allow the telescope fish to see farther, so the range of perceiving the surrounding environment is wider. There is also a fish mentioned in the film, the head is a transparent large-finned posterior anal fish ( Barreleye ). Its eyes are also telescope-shaped and look straight up. To improve their field of vision, their heads have also evolved to be transparent. The transparent head may also act as a lens, helping it to focus light. These fish use stronger vision to detect farther, so what methods do other fish use to perceive wider and sharper?
2. Another biome that lives in mid-ocean ridges looks even more hostile. Not only is the depth deeper, but there are also volcanic eruptions from time to time. There are three times as many volcanic eruptions on the ocean floor as on land. But strangely enough, the biome here is much richer and more complex. In fact, it is because of this volcanic environment that such a rich biome exists. Undersea volcanoes are different from terrestrial volcanoes because magma cools and solidifies more easily in the presence of water. And there will be a large number of hydrothermal vents ( Hydrothermal vents) around these volcanoes , these vents eject minerals, and have a certain temperature (60-464 ° C), providing an environment for biological survival.
In this environment, many bacteria that rely on chemical synthesis (chemosynthetic) thrive. Because a large number of minerals are dissolved in seawater, these autotrophs will use these sulfides, especially hydrogen sulfide, to synthesize some organic compounds. Some Amphipods and Copepods prey on these fungi directly . And some larger organisms will prey on some primary consumers to form a food chain.
Another important component in this environment is the giant tube worm . These tube worms have no mouth and no digestive system, and act like parasites to absorb nutrients produced by autotrophic bacteria on their tissues. The tubeworm's red crown contains hemoglobin, which binds to hydrogen sulfide in seawater and transports it into its body for supply to bacteria.
In addition to this, there is a large number of crustaceans in this biome, as mentioned in the film, including Kiwa hirsuta , Hoff crab , and white blind shrimp ("eyeless" shrimp). 3. The " Lost City " in the Atlantic Ocean is mentioned at the end of the documentary, which is a great inspiration for the study of biological origin. In fact, there are hypotheses supporting the origin of organisms from deep-sea hydrothermal vents. One reason is that the environment around deep-sea hydrothermal vents is very similar to that of the early Earth. In the early days of Earth, the entire planet was hotter than it is now because there was so much carbon dioxide (greenhouse gas) in the atmosphere. The earliest life began 3.5 billion years ago, but the atmosphere did not contain oxygen until 2.3-2.4 billion years ago, so the earth was dominated by anaerobic bacteria at that time. Oxygen levels are low near deep-sea hydrothermal vents, with temperatures between 80-121 degrees Celsius. Surrounded by a large number of hyperthermophiles ( Hyperthermophiles ), the living characteristics of these bacteria are resistant to heat and anaerobic, and these characteristics are very close to the characteristics of life in the early days of the earth. Another reason is that in 2007, geologists discovered 1.43 billion-year-old deep-sea microbial fossils, which also proved that organisms may have originated from the seafloor. (Refer to: Origin of Life for details ) There is a more interesting model to explain the impact of deep-sea hydrothermal vents on biological origin, called the Fuel Cell Model ( Fuel Cell Model )). This model regards the ocean-deep-sea hydrothermal vent as a fuel cell, because the hydrothermal vent is strongly alkaline, with a pH value of around 11; while the ocean at that time was acidic, with a pH value of around 5. Because of the acid-base difference, electrons migrate and redox reactions occur, similar to the batteries we use now. And these reactions create a flow of energy that enables many complex molecules to be produced under these conditions. In fact, chemical reactions caused by acid-base differences, as well as redox reactions play a very important role in living organisms. For example, ATP ( Adenosine triphosphate ), which plays a role in energy cycling in organisms , can exist stably at a pH value of 6.8-7.4, but under a slightly shifted pH condition, ATP is rapidly hydrolyzed to ADP and energy is released.
From the "fuel cell model", we can know that there are acid-base differences, temperature differences and redox differences from the crust (deep-sea hydrothermal vents) to the ocean, resulting in a stable gradient from the crust to the ocean, causing constant chemical reactions, Generate new chemical substances, from simple to complex, from small molecules to large molecules, and gradually form the first life forms. There are studies reporting on the origins of cells . The crust (deep-sea hydrothermal vent) is mainly an environment of high temperature, alkaline and rich in reducing chemical groups. Under the catalysis of FeS, NiS and other minerals, reducing chemical groups (including CH4, NH3, CO, etc.) form a complex The carbon structure is combined, and further forms amino acids, sugars, etc. These molecules are all essential components of living organisms. More biomolecules lead to the emergence of RNA and DNA in large quantities, and the appearance of these molecules also provides conditions for the emergence of the most primitive life forms in the future.
Attachment 1: Shooting area The locations mentioned in this episode include diving from the "Antarctic Sound" of Antarctica at the beginning, to the coast of South America, to the Gulf of Mexico; then from the Mariana Trench in the Pacific Ocean to the South Pacific Ocean Ridges, and finally "Lost City" in the Atlantic Ocean, they have detailed shots of almost every corner. The depth of the shooting is mainly concentrated in the range of up to 1000 meters, and the sunlight is almost impervious in this range. If there is no shooting team in this area, it is basically dark here, except for some biological fluorescence. Also, at this depth, the pressure of the sea water will reach 100 times the normal atmospheric pressure on our surface, and the temperature of the water will be around 4°C. Wikipedia: Deep sea
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