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Does everything in the world need the sun to survive?
Question Date: 2016-05-26
Answer 1:

Until recently, scientists did think that all life on Earth depends on the Sun to survive. Now, I would say that almost all life on Earth depends on the Sun to survive. First, let's talk about life that does depend on the Sun to survive. Let's start by looking at the bottom of the food chain.

Plants do not eat other living things to grow and survive: they are autotrophs because they make their own food. Instead, they use nutrients in the soil and energy from the Sun to make their food (mostly sugar). We named this process photosynthesis (which roughly means "making things [food] from light"). Without sunlight, plants could not survive.

The next level of the food chain is made up of herbivores, animals that eat plants. Since herbivores depend on plants to survive, herbivores could not survive without sunlight.

Most of the rest of the food chain is made up of carnivores, animals that eat animals. Some of these animals eat herbivores to survive: they could not survive without the plants that feed the herbivores. Other carnivores eat carnivores to survive. But in the end, these animals depend on plants as a food source, either for themselves, for their food to eat, for their food's food to eat, or so on.

So what about life that does not depend on the Sun to survive? Deep in the ocean, there are some autotrophs that use energy from the Earth's hot core to make their food. The only examples I know about are bacteria that live near hydrothermal vents (jets of hot water coming from deeper in the Earth). These bacteria use chemicals like methane and hydrogen sulfide and the energy from hydrothermal vents to make their food. We call this process chemosynthesis (which roughly means "making things [food] from chemicals"). Other life forms can eat these bacteria and also survive without sunlight. The only examples I know about are called giant tube worms, riftia pachyptila.

Scientists only discovered these strange chemosynthetic bacteria in 1977. Now we know that life can exist without sunlight, but there are still a lot of things that we don't know about how it works. I would definitely say that humans need the Sun to survive, and we probably always will.

Answer 2:

Surprisingly, no. There are bacteria that live in hot springs and other volcanic water that get their energy from chemicals released as a result of volcanic activity. They do not need light, and they do not need oxygen, and the Earth's interior provides them with heat, so they can live without the sun.

Answer 3:

Most organisms either directly or indirectly use energy from the sun to survive, but not all of them.

Plants and some microbes use the energy from the sun to perform photosynthesis. In photosynthesis, light energy is used to combine CO2 in the air with water to make sugars and oxygen. Any organism that doesn’t perform photosynthesis usually eats an organism that does to indirectly get the energy from the sun. However, there are living things very deep in the ocean near deep sea vents that do not need the sun to survive. They are so far down in the ocean that no sunlight reaches them and they get all of their energy from chemical dissolved in the water near the vents. Also the very first organisms that ever existed didn’t use photosynthesis and got their energy from chemicals like deep sea vent organisms. In different sense, every organism needs the heat provided by the sun because then the entire Earth would be too cold for any life to exist. So not every organism needs the energy of the sun for food, but all living things need the heat of the sun to survive.

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