Ode to the Pale Blue Dot

Regardless of species or locale, we all share a common, vital asset: the very planet we call home. With its immense beauty, this “Pale Blue Dot” (1) provides us far more than just a place to live. It is home to complex ecosystems working together in astonishing ways, creating the perfect conditions to sustain us all. Which is why celebrating this miraculous planet only one day a year feels like a non-tribute, a woefully underwhelming afterthought. Discussions of our home must be front and center of our attention everyday. But Earth Day offers us the opportunity to engage with and appreciate the many ways in which we rely on Earth, and why it is so urgent to protect it. On this day, we celebrate Earth by honoring the ways it has come to support our lives. 

Earth Day presents a topic very close to home for scientists and science enthusiasts who specialize in soil health. We are especially curious about ecosystem complexities, and even more eager to share our findings with the world. We believe that a passion for learning and knowledge-sharing is vital to enabling ways in which we, as a species, may benefit from our planetary ecosystem in a sustainable way. 

As terrestrial organisms, when we look down upon Earth, what we see is most often soil. It is only natural then, that “soil” and “earth” are used interchangeably. Soil is the skin of our planet. In just one tablespoon of soil, we can find more living organisms than there are humans on all of earth. Think about it like this: imagine having hands big enough to hold all of Earth’s humans with plenty of room to spare! That’s how large we are when compared to these miniscule organisms. Though small, these powerful life-giving forces have worked together with other life forms for billions and billions of years, building this place we now call home. In fact, all of life during the billion + years of the Archean era, was strictly bacterial. (2)

A key point in time in the history of microbes on our planet dates back to about 3.5 billion years ago, when photosynthetic bacteria are thought to have first appeared on Earth. These bacteria, known as “cyanobacteria” or “blue-green algae” formed adhesive structures on the surfaces of rocks in calcareous mounds, made of layers of the lime-secreting cyanobacteria and trapped sediment. These structures called “stromatolites,” are responsible for introducing oxygen into our atmosphere. Cyanobacteria are still around today, and are one of the largest and most important groups of bacteria on Earth. Many Proterozoic oil deposits are attributed to the activity of cyanobacteria. They are also important providers of nitrogen fertilizer in agriculture and often play a key role in maintaining the stability of the surface crusts of semi-deserts, and the fertility of farm soils in arid regions. Cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout Earth's history. Before they emerged during the Archaean and Proterozoic Eras, the Earth’s atmosphere had a very different chemistry, unsuitable for life as we know it today. (3)

What’s more, plants are able to photosynthesize today thanks to a special cooperation with cyanobacteria, through “endosymbiosis.” This process involves a unicellular protist engulfing a free-living photosynthetic cyanobacterium and retaining it, instead of digesting it in the food vacuole. The captured cell called the “endosymbiont” was later reduced to a functional organelle bound by two membranes, and transmitted vertically to subsequent generations. This unlikely set of events established a new eukaryotic lineage supergroup called "Plantae," encompassing many photosynthetic algae and land plants. (4)