An Astrobiology Perspective on Ecosystem Services

“Biota control the basic chemical conditions on the surface of the Earth. With an atmosphere containing 21% oxygen, the chemical environment on Earth stands in start contrast to that on our sterile planetary neighbors–Mars and Venus. The metabolic activities of organisms, which link oxidation and reduction reactions, produce the relatively stable conditions on Earth that are conductive to the persistence of life.”

– William Schlesinger, Biogeochemistry 2^nd Ed.

Venus, Earth and Mars

Imagine You are a Space Traveler…

Sometimes it can be helpful when framing an issue to get some perspective. When it comes to classifying the values that the vital functions that Earth’s ecosystems provide us, this perspective can be gained by zooming way way waaay out from the bird’s eye view of life on Earth to that of a space traveler who can not only see Earth, but other planets too. This interplanetary perspective falls into the academic domain of astrobiology.

As commented on by Schlesinger in the introductory quote, Earth stands in marked contrast to its sister planets, Mars and Venus. The latter two planets are both inhospitable to life as we know it, but in different ways. Venus has a runaway greenhouse effect and is too hot, and Mars has a runaway refrigerator effect and is too cold. (This is a ripe setting for an interplanetary Goldilocks tale don’t you think?)

The Critical Function of Regulating Ecosystem Services

Photosynthesis and Respiration

One of the key factors that makes life on Earth possible is life itself. It does this by maintaining a  system of chemical metabolic  pathways. (If you want to blow your mind with the complexity of these biological pathways, download the chart from this Sigma site.) The largest source of energy driving these pathways is the sun, which provides us with an endless stream of solar radiation. The most well know, and arguably most important biological chemical processes, are respiration and photosynthesis, which–as we all learn in grade school–are essential to the functions of regulating oxygen (O₂)and carbon dioxide (CO₂). Life also helps to regulate other important biogeochemical pathways as well such as nitrogen, sulphur, water and phosphorus.

The simplified diagram below breaks down the central role that biota on Earth play in regulating Earth’s chemistry in such a way that it maintains relative homeostasis (similar to how our own bodies maintain our blood chemistry) over time, compared to Venus and Mars. The figure highlights the important role of CO₂ in the atmosphere as well.

Venus-Earth-Mars Comparison (Image from Nick Strobel's Astronomy Notes.)

Plants and other organisms that photosynthesize create the matter (biomass) which forms the base of the food chain on Earth. Over time green plants/organisms sequester carbon dioxide from the atmosphere into their living tissues, and this is called net primary production (NPP). This photosynthetic process, along with respiration, in turn, also helps in regulating  oxygen and carbon dioxide cycles which are critical to life on Earth as we know it. Hence, the amount of food available on Earth, as well as the composition of the atmosphere is significantly regulated by the balancing act of the actions of photosynthetic organisms (autotrophs) and respiring ones (heterotrophs). Maintaining biodiversity is also important to maintaining this balance.

Humans control about 40% of the Earth’s terrestrial primary production.

How much these life processes help protect the Earth from turning into a dead planet like Mars or Venus is debatable, but what we DO know is that humans on Earth control about 40% of the total terrestrial net primary production from plants, as well as about 8% from the oceans. 40%!! This is an astounding number! And, these numbers were calculated based on data from a couple of decades ago, so the actual numbers are likely higher today.

What this means is that humans are significantly commandeering and influencing some of the vital life processes on Earth of net primary production and influencing their related chemical pathways. In some ways, we really are space travelers, and Earth is our spaceship. As our population rises on this vessel of ours, we are likely to push these numbers higher and higher over the next couple of decades.

This brings up some key questions relating to how we are impacting the regulatory functioning of Earth’s natural systems:

• If we think of putting a virtual green light, yellow light and red light warning system for risk to spaceship Earth’s critical life regulatory functioning, what level of human impact is acceptable (within the green range), risky (within the yellow range) and dire red alert?
• How can we reduce the human impact on ecosystem regulatory functions that impact life support on Earth to levels that in the safe green zone?
• Considering that we have already failed in our attempts to secure biodiversity, such as achieving the Convention on Biological Diversity 2010 targets, how will we achieve the next set of targets effectively in the face of concurrent growing human needs?

Ground Control to Major Tom, what do you think of that?