The Crazy Connection Between Color And The Existence of Life

There is an extremely deep connection between life on Earth and the colors that we see. On the surface, this connection is very basic and well studied, but as we delve deeper, the questions become more profound and less explored or known. I will start from a simple question and keep asking why. Stay with me.

The first question is, “Why do we see the colors that we see?” To answer this question on a purely physical basis, it is important to understand how the eye functions. In our eyes, we have cone cells, which are sensitive to different wavelengths of light. These cone cells, named S-cones, M-cones and L-cones, are sensitized to light of wavelengths 420–440 nm (blue), 534–545 nm (green), and 564–580 nm (red), respectively. By combining the relative signals from these three types of cone cells, our brain can see a fairly continuous range of colors (10 million different colors in fact!). Thus, we see the colors that we see because these colors are just different frequencies/wavelengths of light that our eyes are specifically tuned to pick up.

2000px-Cone-fundamentals-with-srgb-spectrum.svg

So now we must ask, “Well, why did our brains evolve to see those specific colors?” It is generally agreed upon that animals have evolved to see colors primarily to alert them to potential sources of food. For instance, certain birds are sensitized to the ultraviolet spectrum which allows them to sense UV patterns found on flowers and other wildlife that are otherwise invisible to the human eye. Similarly, it is thought that the evolution of trichromatic color vision in humans occurred as the result of our primate ancestors switching to greater daytime activity leading to a greater reliance on consuming fruits and leaves that were green, red, and orange in color.

Going deeper, the next question asks, “Well, I understand that animals evolved to see certain plants, but why are these plants colored this way to begin with?” To answer this question, we must understand how pigmentation works on a chemical level. Pigments are “molecules that absorb specific wavelengths (energies) of light and reflect all others.” In order for a particular molecule to reflect a certain color, its chemical structure must be arranged in a special way. Specifically, the molecule’s electrons must be able to absorb certain wavelengths of light, but not others. Take chlorophyll for instance. Chlorophyll’s chemical structure causes it to absorb blue and red light, but hardly any green light at all, so the green gets reflected back to our eyes, which is why leaves appear green. In fact, Chlorophyll takes the energy its electrons absorb from light, and through a series of chemical steps (called photosynthesis) takes carbon dioxide and water and, using the energy from the sun, converts them into sugars and oxygen. As a result, plants get their mass from the air by turning carbon dioxide into sugars, not from the roots as is a common misconception. This process is virtually the opposite of the process discussed in my article, “When You Lose Weight, Where Does it Go? The Answer May Surprise You“.

plant_photosynth1

Now, why do pigments like chlorophyll absorb wavelengths of light in the visible spectrum? The answer is a Goldilocks effect of sorts. If plants had pigments that absorbed UV and x-rays, too much energy would be absorbed, causing electrons to be knocked off their orbitals, destroying the molecule. On the flip side, if plants absorbed infrared and radio waves, there would not be enough energy for electron transfer and the photosynthetic reaction could not take place. So basically, pigments absorb in the visible spectrum because these frequencies provide just the right amount of energy for powering crucial chemical reactions.

At this point, lets just reflect on our journey so far before we delve even deeper. We’ve gone from asking why we see the colors we do, to why we evolved to do so, to why these colors are the colors that they are, to finally understanding why biological pigments have evolved to use these specific colors. Now, the next set of questions will force us to think about the interactions between color and the existence of life on Earth.

Absorption_spectrum_of_liquid_water

Given that life first formed and evolved in water, how does this relate to the visible spectrum of color? If you look at the chart above, you can see how much light is absorbed by water at different wavelengths – the higher the line on the chart goes, the more light gets absorbed and not passed through. Amazingly, water absorbs the least amount of light right in the visible spectrum, which allows more visible light to pass through, and hence why water appears transparent to us. This means that if you are an early form of photosynthetic life in the ocean or a pond, you are still able to get the light you need to survive and thrive. This is unlikely a coincidence, but merely another reason why we see the light that we do. Not only is the light we see of ideal energy for supporting life, it is also able to easily pass through water.

bbrc6b

We’re still not done. Consider this: “How does the light we see relate to the light that is emitted from the sun?” The chart above is what’s called a Blackbody Diagram. You may not realize this, but all objects radiate electromagnetic radiation according to a specific spectrum and intensity that depends solely on their temperature – even humans do! People, however, are relatively cool in temperature (98.6 F) and as a result, radiate primarily in the infrared spectrum so we can’t see it with the naked eye. Stars on the other hand, which are much hotter, tend to radiate closer to the visible spectrum, with relatively cool stars appearing red and super hot stars appearing blue. Incredibly, you’ll notice, that our star, which is categorized as a white star, is at a temperature that causes its blackbody diagram to peak right in the middle of the visible spectrum. In fact, 44% of the sun’s energy is emitted in the narrow band of electromagnetic radiation that comprises visible light. So visible light is of ideal energy for supporting life, able to easily pass through water, and also corresponds to the most light that is emitted from the sun. Wow!

Given all of these connected pieces of science, I can’t help but marvel at the elegance of the universe. Putting these pieces together opens up much deeper questions, ones that I can’t even hope to answer. Can life exist on a planet orbiting a star of a vastly different temperature? If it can, will life on this planet be incredibly different and optimized to the specific frequencies of light that are most prevalent? Could life exist at all if water had a different absorption spectrum that did not bottom out in the visible range? How much leeway on these physical properties does the universe give life, and do these properties all have to overlap? Will life find a way no matter what? Are these properties specifically designed to coexist perfectly, or do we just happen to exist on a planet, orbiting a star, in a galaxy, within a universe in which all of these things are possible? Are we only capable of asking these questions because all of these things are true to begin with?

These are the questions we must all answer for ourselves and are at their essence the same questions humans have been trying to answer for thousands of years.  Thank you for reading and would love to hear your perspectives on all of this.


If you would like to learn more about the science of color, check out this great series from RadioLab

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14 thoughts on “The Crazy Connection Between Color And The Existence of Life

  1. But part of the ‘color’ aspect is the mind’s interpretation of it as a hue. This could be true whatever spectrum we got to see. Nothing says that red or blue (as perception of hue in the brain) has to correspond to the specific frequeny spectrums they are know.

    We could see all the colors we see as frequencies inside the infrared spectrum, for example. Infra-red is just a name based on that we see those frequencies as beyond the red one’s currently.

    Like

  2. Another interesting connection is the frequency response of the Earth’s atmosphere. http://en.wikipedia.org/wiki/Atmosphere_of_Earth#/media/File:Atmospheric_electromagnetic_opacity.svg

    Similar to the frequency response of the earth’s ocean, the atmosphere also has a “gap” in the filter around the visible light spectrum. How would photosynthetic life have survived on Earth if the constitution of the atmosphere filtered out most of the visible light energy? And an even more provocative question: did Earth’s biota evolve to emit gases that in turn changed the frequency response of the atmosphere to maximize transmission of visible light energy?

    Liked by 1 person

    • Keith,

      Super interesting! Wish I would have seen that and included it in the article. Thanks for pointing that our to me. Very interesting question whether life creating this or this created life.

      Like

  3. I think the most striking thing is that the peak of the sun’s blackbody spectrum coincides with the valley of water’s absorption spectrum.

    I also think that, to answer a lot of your questions we have to find out whether life that today lives in deep ocean hydrothermal vents can develop independently from, or in the complete lack of, surface life that depends on energy from stars. Of course, this life instead depends on water remaining liquid at such incredible pressures and high temperatures compared with surface life. If water didn’t remain liquid, it’s absorption properties would undoubtedly be different, leading back to one of your questions.

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  4. Why do plants have different pigment colors? Why do some plants change these pigments throughout the year?

    “As a result, plants get their mass from the air by turning carbon dioxide into sugars, not from the roots as is a common misconception.”

    Don’t they get mass from water as well, which they get from their roots?

    Like

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  6. I hae scientifics questions about the operation of negro color receptors, can the see friend chicken special or perhaps dee watermelons?

    It is a ligigintimate scentific questions!

    Like

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  8. Another example of how the universe seems to be fine-tuned for life! This means that vision in the visible spectrum is important for survival of life. Most visual animals see in this spectrum, although there is some variation into the ultraviolet as well. We would therefore expect alien life forms that are visual to most likely have evolved vision in this range also. Note, this article does not explain qualia—that is, why red looks like red and not blue or something else. colorblind individuals have pigment variations and see the world a bit differently. There could be a variation on chlorophyll on an alien world that would produce different colored plants (to our eyes). Another interesting thing is that the pigments in plants such as carotenoids, flavenoids, and hundreds of others act as antioxidants that help to fight free radicals that might damage cells. Other amazing and unique properties of water that are essential to life are its lesser density as a solid, so ice floats on the top of water preventing underwater life from turning to ice, the incredible properties of water as a solvent, its ability to diffuse producing osmotic gradients, its ability to act as an anti-friction lubricant, its ability to act as a heat sink, minimizing changes in temperature in a body, its ability to cool with evaporation such as sweating, its properties of adhesion, cohesion, surface tension, and capillary action, its buffering ability, and the structured water concept of Dr. Gerald Pollack.
    If water had any different properties life could not exist as we know it.

    Like

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