Sorry this round is a bit late; I've been having some technical difficulties!
For this first round of research of this brand new cycle, I will be providing some background information which will hopefully make my future, more complex installments more comprehensive and cohesive.
So, what is it about Earth that makes life on this planet possible? Well, first of all, Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases not only contains the air that we breathe, but also protects us from the blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night, and contains the rights kinds and right amounts of chemicals to allow life to form. The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds Earth, and is comprised of 6 layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, the ionosphere, and the exosphere, each layer performing a different function. (1) The troposphere is the densest part of the atmosphere, and is where almost all weather patterns are found. The stratosphere is where the ozone layer is found, which absorbs and scatters solar ultraviolet radiation. The mesosphere is the layer in which meteors burn up. The thermosphere is where satellites at aurora can be found. The ionosphere is an abundant layer of electrons and ionized atoms and molecules that overlaps into the mesosphere and thermosphere. This region grows and shrinks based on solar conditions and and is a critical link in the chain of Sun-Earth interactions. Finally, the exosphere is the upper limit of our atmosphere that stretches up to space. (1,2) Our atmosphere is incredibly unique in that its temperature is relatively mild, the climate is regulated, and it allows the circulation of water to take place. Without each and every one of these details, life would not be possible. (2)
But, what other elements impact life on Earth? Well, one thing that makes our planet unique is water. Water is believed to be the most important chemical compound necessary for life, as it contains oxygen and allows life-providing molecules to move around easily. Water on Earth can be found anywhere, in its three states, while on other planets it is usually found in its gaseous or solid state. (3) This brings us around to another important factor of life of Earth: temperature. Earth is situated from the sun at such a distance that it receives the perfect amount of solar energy from the sun, allowing life to form. The temperature is maintained by the moderate amount of carbon dioxide in the planet's atmosphere, which is constantly refreshed whenever there is a volcanic eruption. The temperature on Earth does not go from one extreme to the other either. Mercury, for example, can be anything from 200°c below freezing to 375°c above. Because we live in this "Goldilocks Zone", and because Earth has such a regular climate, life is possible. (4)
We also have the right conditions off of our planet, apart from the sun, specifically because of our moon and neighbouring planets. Our large moon ensures climate stability by minimizing changes in planetary tilt. If our planet didn't have a tilt, it wouldn't have seasons. However, a severe tilt would result in extreme seasons. The moon is also responsible for the ocean's tidal flow, which helps transport heat from the equator to the poles. Without the lunar tides, it's conceivable that climate oscillations from the ice age to the interglacial would be less extreme than they are. This would result in our marine environment would be much less rich in terms of species diversity, and life on Earth could have evolved very differently (or not at all) if our moon had been any different. (5)
What's more is that because of the other planets in our solar system, particularly those closer to the Kuiper Belt, like Jupiter, we are shielded from many of the meteor and asteroid strikes that would have bombarded our planet had they not been in the way. Without Jupiter, for example, and its incredibly powerful gravitational pull, we would be susceptible to 10,000 times more stellar strikes, as the gas giant would fling the comets out of out our way before it could do any harm. (6)
So, from gathering this information, it is easy to see that life is extremely fragile. Without any of the details listed above, we would not exist. The thought really does make one wonder if there is life elsewhere in the universe, but considering the overwhelming size of the universe, it is entirely possible, if not probable. It also raises questions regarding what qualifications a galaxy may need to meet in order to support life; something I will look into in my next round of research.
My sources for this post were:
Thank you all for reading! As always, if anyone has any comments, suggestions, questions, or critiques, don't hesitate to contact me! I always appreciate feedback.