Sunlight touches most of life on earth in many ways. It's one of the foundational sources of energy in our environment. The position of our planet in space relative to our sun creates a unique situation for seasons, habitats, migrations, and behaviors to exist. Although it never touches the earth, the sun is a vital part of our existence. So where are all the places the light touches? Let’s get into it!
Why do we have seasons? The Earth is positioned in just the right way that allows for these unique variations to exist. Just a little farther away and it would be too cold, and just a little closer and all the water would evaporate. But not only that, the earth is tilted on an axis that, as the earth rotates around the sun, varies the amount of sunlight hitting different sections of the earth at different times of the year. During the summer in either the northern or southern hemisphere, that half of the earth is angled more towards the sun, which allows more sun energy to hit the earth in a given area for a longer duration of time. As the earth continues around the sun, the angle changes and the same hemisphere is then given less sunlight within the same area for a shorter duration. The earth’s axis is not shifting though, just our position around the sun. This change is just enough to turn water into ice and beach days into snow days.
The sun provides the energy for the base of the food web. In temperate zones where there are seasons, there is not enough light energy to photosynthesize during the winter, but in the summer, photosynthesis and growth are in full swing. Photosynthesis takes place in the chlorophyll of the plants, where light energy splits water molecules into Oxygen and Hydrogen molecules. The Oxygen molecules then pair together making the O2 molecule, which is just an unneeded byproduct, so it is expelled from the plant. This fills our atmosphere with the oxygen that we and other aerobic creatures use to breathe. The Hydrogen can then be used for the creation of the sugar.
When bonds in molecules are broken, the energy used to hold them together is captured in molecules called ATP and NADPH, which is then used to create that sugar. Just like we use the oxygen byproduct from plants, the plants use carbon dioxide, which is the byproduct of our cellular respiration reactions that generate our own energy. This carbon, oxygen, and hydrogen is combined using the energy captured in the ATP and NADPH to make C6H12O6 sugar molecules that the plants will use for energy and store away in the winter to fuel their regrowth in the spring. This is the same sugar that is captured by humans to make maple syrup. So next time you’re having your breakfast of pancakes or waffles, don’t forget your topping of converted sun energy!
This burst of life in plants drives the following boost in insect life as well. Many insects depend upon not only the plants and the food they provide, but also the sun as well. In fact, as cold-blooded animals are not able to generate their own body heat, many insects need the air temperature to be about 55°F to even move their muscles. Bees have learned to use the sun in a unique way as well. Bees work together as a hive to find flowers with nectar and pollen to make their honey, and they use the sun to communicate directions to the best flowers to each other.
To understand the language of the bees, we have to imagine the top of the hive wall representing the direction in which the sun is positioned when the bee exits the hive. From there, the bee waggles their abdomen, or butts, in the direction of the flowers relative to the sun’s position when they exit the hive. The duration of the waggle represents the distance. And they even adjust the angle as the sun moves across the sky. If the waggle is towards the bottom of the hive, then the bees have to fly in the opposite direction of the sun when they exit the hive. If the waggle is to the right, then the bees have to go to the right of where the position of the sun is, and etc. If this makes sense to you, then you understand the language of the bees, aka, the waggle dance.
It's not only the insects that take advantage of the benefits of sunlight. Migratory bird species move to the tropics to avoid harsh winters, but why even bother putting the energy in to fly all the way back? As mentioned earlier, in the spring, plants begin to grow and produce a lot of seeds and fruits, as well as attract insects, all of which are on the menu for birds. This boost in the production of energy provides a wealth of resources for birds to gather the energy to produce their own offspring, but if they can find this in the tropics year-round, why bother leaving?
Well, there are a couple reasons to leave. First, during the winter, the tropics are packed with native bird species and the migratory bird species all competing for space and food. If there is a space back up north or south or the tropics with lots of resources and not a lot of competition, then it's highly beneficial to take advantage of that wealth. Also, in the summer, the closer to the poles you get, the longer the day is. This increase in the duration of sunlight gives the birds more time to find food, build shelters, and get down to it.
For life to exist on land, water has to be a part of it. The sun gives the energy to drive the process of water evaporating off the oceans and then depositing onto the land as rain and snow. But this isn’t always just a peaceful rain or snowfall. Water has a high specific heat, which means it takes a lot of energy to heat it up. This is why, although the summer begins in June, your pool is always cold until the end of July. It's the same for the ocean temperatures too, which are not warm enough for the peak hurricane season to begin from August to October. For these 2-3 months, the sun heated ocean fuels these impressive demonstrations of the power of nature.
But the sun drives the cold weather events as well. Sun energy drives the evaporation of water into the atmosphere, and if it is cold enough when it condenses, it comes down as snow. In my area of the world in the Northeast United States, we are uniquely positioned to have the gulf stream ocean current, also powered in part by sun energy, drive moist air up north from the gulf of Mexico to our region, where it is met with cold air from the north. This collision of warm moist air and cool dry air creates big storms called Nor’easters, which can sometimes drop multiple feet, even close to a meter of snow! As climate change increases the average temperatures of the earth, the atmosphere will be able to carry more water, increasing the amount of rain in hurricanes and the amount of snow in nor’easters.
Even if the water returns to earth as snow, the sun still melts a lot of that snow into water, which then fills the rivers and lakes as it makes its way back to the ocean. This process not only creates seasonal habitats for species like salmon, but also provides close to 75% of water resources for some areas like the western U.S.A.
Hopefully I’ve been able to shed some light on not only how important the sun is to the earth, but also our unique relationship to it is. Our sun drives the seasons, life, behaviors, and the creation of habitats. As the conditions of our climate change, these variables will also change and hopefully adapt. It’s all connected.