There is much debate to what the limits of life are, after all, we only have to look at the deepest depths of our oceans or at acidophilic microorganisms to recognise that life can survive in inexpedient and strange environments.
There is however a few key ingredients that I am sure we can all agree are a necessity for life as we know it, here is a non-exhaustive list.
To our extreme advantage, Earth is situated in the solar system at a location where temperatures allow water to be naturally liquid. Water has acted as a “primordial soup” – a place to harbour the ingredients of life such as DNA and Proteins and as it is an excellent solvent, it has the advantage of being capable to dissolve many substances creating a hub for biochemical activity.
Another benefit of water is its properties when frozen. Water in its solid form is actually less dense than it is as a liquid; this means ice floats and hence insulates the liquid water beneath it from freezing further. If ice was to sink, this would allow layers of water to freeze above it and inevitably all liquid water would become ice, making the chemical reactions for life near impossible.
It may be obvious, but without energy virtually nothing can happen. The Earths most obvious source of energy is the sun. Our host star is the driver of many important functions, including photosynthesis; which provides the nutrients required for the bulk of life on earth, both directly and indirectly and provides us with an atmosphere that is about 21% oxygen, just right for respiration. The Earth’s atmosphere is very unique as it has free oxygen (O2), this is strange as oxygen loves to chemically react with other atoms and molecules. The oxygen in our atmosphere would disappear if photosynthesising organisms like plants and cyanobacteria did not regenerate it.
From plate tectonics to the carbon and water cycles, the recycling of materials and compounds is a natural process on Earth. Carbon dioxide is often stored in rocks, if it was to stay there the Earth would surely become a lot colder, but it is returned to the atmosphere through the action of plate tectonics and the resulting volcanic eruptions. Similarly water is recycled in the environment, from the precipitation that rains on the land, to the evapotranspiration of trees and plants to the evaporation of surface waters, the Earth has a way to ensure that there is recycling pattern for its most important molecules to be circulated throughout our environment.
Time has been instrumental to life here on Earth. This is mainly again to the credit of our sun. Scientists have argued that habitable worlds need a star that will live at the very least 7 billion years, and we are lucky enough to be revolving a star that will have a very long life. Time is paramount for evolution, the earth is about 4.6 billion years old, but life has not always prospered here. The first known organism appeared here around 3.5 billion years ago, multicellular organisms did not appear till 600 million years ago. Evolution is a very slow process and each and every one of us is a product of a vast amount of time.
Of course, all of these things are the basis of life here on Earth, but we must remember that we have evolved to utilise what is present in our global environment. While we are the only known planet to harbour life, continued exploration might pave way to the discovery of similar planets, or indeed planets where life has blossomed under different parameters may be found.
But until then, remember how truly remarkable we all are.
Photo courtesy of NASA's Messenger spacecraft.
The age of Earth:
The Carbon Cycle: