A lot of good things are green. Green tea, green apples, broccoli's "green chemoprevention," greenery that reduces stress, trees that breathe oxygen into our air. Green is the color of spring, new life, calmness, and is many times associated with health, too.

Indeed, we gravitate toward the color green for fairly obvious reasons — it brings us closer to nature, it creates a soothing environment that improves our mental health, creativity, and focus (see the benefits of ecotherapy), and it’s often the color of healthy, leafy vegetables that are good for our minds and bodies. But it turns out that humans’ deep connection to the color green may be far more primitive and ancient than previously imagined: it might have to do with photosynthesis and oxygen-making processes, which all life on earth relies on.

A new study out of Imperial College London, published in the journal Molecular Biology and Evolution, examined genetic sequences from 200 species of cyanobacteria, which are able to photosynthesize (photosynthesis is the process used by plants and other organisms that take sunlight and convert it into chemical energy as fuel). The researchers examined certain plants and algae, focusing primarily on a gene called D1 — which helps photosynthesis occur by removing electrons from water and using them.

Previously, scientists believed that oxygen-generating photosynthesis began about 2.4 billion years ago. But the researchers of the new study found that D1 has at least five varieties and many of them “have extremely ancient characteristics,” Dr. Tanai Cardona, an author of the study, told The New York Times. It turns out these cyanobacteria, or ancestors of them, may have filled the earth’s atmosphere with oxygen billions of years earlier than we thought. Oxygen was the foundation for life and all things green — and its existence on earth is quite ancient.

While things associated with green (plants, nature, food, oxygen) are essential to our survival, we often allow the color green to fall into the backdrop. As a cooler color, a mix of yellow and blue, green is frequently defined as a background color. The background of a traditional painting, for example, is often green and blue while the object of interest in the forefront is painted with warmer colors like reds or oranges. Green is easier for us to forget, according to a recent study that found people were more likely to remember red and yellow than blue and green.

But if green is easy to forget or pass over, why do we still remain drawn to it? Green is often associated with harmony, peace, and improved mental health (plenty of studies have shown that closer proximity to parks and greenery is linked to lower rates of depression and anxiety). So while it may not be at the forefront of our attention, having plenty of green in the background of life is extremely important.