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What can live without sunlight?
Question Date: 2019-08-29
Answer 1:

Good question Laniyah! There are a number of life forms that have adapted to living in underground caves that have no light! For example, I research a species of fish, Astyanax mexicanus, that is found in underground limestone caves in Mexico. This fish evolved from river-dwelling fish that washed into caves. After around 200,000 generations in the absence of light, the fish have lost their eyes and pigment while at the same time gaining adaptations that allow them to survive in the harsh cave environment. Since there is no light, plants cannot live in the cave, meaning that there is not much to eat. The cave fish have adaptations that allow them to survive long periods with no food at all! They binge eat during the rainy season when floods wash dead material into the cave. Here is a link to a picture of the eyeless/pigmentless cavefish and their river-dwelling cousins.

Blind cavefish

Answer 2:

Energy, oxygen, temperature.

Sunlight influences life through both fairly direct and indirect means. A direct influence is by providing energy which plants and phytoplankton use (through photosynthesis ) to produce molecules which feed themselves. Moving up through the food chain, the sun also provides energy indirectly to most organisms on Earth because nearly all eat plants, or eat which eats those organisms, and so on.

There are, however, some organisms which use energy from other sources. In particular, the deep ocean has hydrothermal vents which support life without the need for sunlight. These jets of hot water from deep in Earth also contain various chemical and mineral compounds that certain bacteria can use in a process called chemosynthesis to produce food molecules. These bacteria replace sunlight-based plants as the bottom of the local food chain supporting other bacteria, tube worms, fish, and more. Thus, in the sense of living without the energy from the sun powering an organism, any which ultimately depend on chemicals from hydrothermal vents can live without sunlight.

But, as hinted above, there are less direct means by which the sun is vital to life. A side produce of photosynthesis is gaseous oxygen. This oxygen is used by the vast majority of organisms to break down food compounds, in the process of cellular respiration. Without the sun, and therefore without this oxygen, most life would not be able to survive. As before though, there are exceptions. Some single-celled organisms ( and at least 3 species that are multi-celled) are able to survive oxygen-free environments. These types of organisms are called anaerobes. Among these are some of the bacteria which live near the aforementioned hydrothermal vents. (Though the other organisms in those ecosystems do need oxygen and therefore would not be able to survive without the sun.)

Another, somewhat indirect, benefit to life of sunlight is heat. Without sunlight, Earth would be much colder. For example, parts of Pluto are as cold as -240°C (-400°F). Even farther out in space, the temperature drops to -270°C (-454°F). At these low temperatures, any liquid water would freeze.

Liquid water has many properties important for life, and (so far) there are no known organisms which do not require water. It is possible to imagine that life could use some other solvent which does not solidify at these temperatures, but none are currently known.

Also, there are a few organisms which can survive periods of extreme cold and without liquid water (notably tardigrades), but do so by becoming dormant; that is, they no longer carry out the typical operations of "living". Note though that getting heat from sunlight is not a requirement for life. An environment kept warm through other means could also support life. This is the basis of some thoughts on how life might survive on rogue planets (i.e., planets without a sun). On Earth though, that energy is probably related to the sun and sunlight (exception: nuclear energy).

[Also see these ScienceLine - questions. ]

Answer 3:

In the depth of the ocean where the sunlight can never reach, there are openings on the seabed called hydrothermal vents. Sea water can come in and get heated. The hot water leaves the vent and often carries chemicals. There are some bacteria live off those chemicals. In turn, clams and shrimps eat those bacteria. It turns out that there are a lot of animals and bacteria that live without sunlight.

Answer 4:

There are organisms in the deep sea that do not need sunlight to survive and proliferate. For instance, there are microbes that use minerals dissolved in the waters near deep sea vents. There are worms and small insect-like creatures that feed on the microbes, and these worms and creatures also do not need sunlight. Researchers are still discovering new organisms that live in the deep sea without need for sunlight, and we have not yet researched much into organisms in deep caves and other places without sunlight.

Answer 5:

In theory, anything can live without sunlight.Even plants that live on light only require light of the same colors as sunlight - it does not actually have to be from the sun.

We often say that life requires sunlight because the sun is the source of almost all power on Earth (what little that isn't solar is geothermal). Without the sun, most of life would indeed die, because there wouldn't be enough energy (and because the Earth would freeze), but it's all because of the amount of energy that the sun supplies, not that it is the sun that is providing said energy.

Answer 6:

Everything except green plants can live and grow without sunlight. Plants get energy from sunlight to do photosynthesis, but the rest of us can't do that - animals and mushrooms and such.

Answer 7:

Creatures live without sunlight deep beneath the surface of the sea. Tube worms, crabs, fish, shrimp, and 100s more species live at underwater hydrothermal vents The water at vents can be hot enough to melt lead. The vents release toxic chemicals. Bacteria make food from the chemicals released from the Earth's core.

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