Why is most plant life on Earth green?

Question

Just go outside.
Look at trees, grass, bushes, ect. Why is it all green? Like why aren’t they all different colors? Why does it mostly all have to be green?

In: Chemistry

Answer 1

I haven’t seen the complete right answer on here so I’ll answer. Solar energy engineer here with a PhD in materials science for solar applications, and many years experience in the solar energy industry.

Our sun emits light (duh). The “white light” that we see from the sun is actually many colors combined together. In fact, when you see a rainbow, this is simply visible sunlight split up into all those separate colors – red, orange, yellow, green, blue, and also a bunch of colors (like ultraviolet, or even a few x-rays) that our human eyes can’t even see.

It turns out that some of the colors that the sun emits are more common than others (look up “Plank’s Law”). It turns out that the most common color that the sun emits is yellow (about 550nm wavelength, for those who are curious), whereas x-rays and gamma rays are pretty rare. Our human eyes have evolved to detect the most common colors of light that come from our sun… we call this the “visible spectrum” which ranges from red to violet.

Similar to humans, plants have also evolved to get the most out of our sun. Plants need energy from sunlight to power themselves.

So, plants evolved a chemical called chlorophyll which is able to absorb the most abundant colors in the solar spectrum, and convert this light-energy into chemical energy for the plant to use.

As I said earlier, the most abundant color in the solar spectrum is yellow. So as plants evolved, they developed chlorophyll which is really good at absorbing yellow light.

The way our human eyes work, if you take yellow out of the spectrum of visible light you end up seeing green. So if we look at a plant, and that plant is sucking up all the yellow light from the sun, then our eyes see the light that ISN’T absorbed… which looks green.

That is why plants are green.

Edit: plants absorb blue and red light, not directly yellow light. This ends up maximizing their energy harvest from the sun. This is slightly more nuanced than just absorbing yellow light, but the idea is the same… to get the max energy out of sunlight.