1.1.3 Habitable environments
Earth is our only reference for what can be defined as a habitable environment for life. However, the conditions needed to sustain complex animal and plant life on our planet are less diverse than those needed by microbial life. You will learn more about microbial life in Section 2.
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Before we move on, what do you think makes the Earth habitable to life?
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The Earth has both land and sea, allowing for a range of species diversity to evolve. There is a moderate amount of oxygen in the atmosphere (and dissolved in water) to allow animals to respire, an ozone layer to protect life from harsh radiation from space, and has an environment (temperature, climate) that is reasonably stable, regulated by complex systems such as the water cycle and plate tectonics. The Sun also provides light for plants to photosynthesise, and heat energy.
You will realise that the Earth system is complex – it balances many different and important interactions between land, sea, atmosphere, and its components to maintain a balance that means Earth can host life. Any changes to this system, such as those we are experiencing through the input of human-derived carbon dioxide (CO2), can upset this balance.
As we explore other planetary bodies, we must be sure that we are not inadvertently disrupting another potentially habitable environment, since this could have dire consequences for extraterrestrial ecosystems, and even limit our own future search for life in the Solar System.