As I started to say last week, Earth is completely unique and amazing! It is the only place in which human life is even vaguely possible, and here’s more evidence to prove that.
The Soldiers Surrounding Us
What most people don’t realize is that the planets surrounding us actually protect us and that without them, we probably wouldn’t be alive. Jupiter, which is more than 300 times more massive than the Earth, protects us from comet impacts in two ways. Firstly, it acts as a shield to block them from us and secondly, it uses its gravity to pull in comets that would otherwise hit the Earth. Saturn and Uranus do the same thing (though at a smaller scale).
In addition to protecting us from comets, the planets also protect us from asteroids from the asteroid belt. Mars, since it is at the edge of the asteroid belt, acts as our first line of defense. Venus also takes a lot of hits for us too.
Our Sun is Special
Many textbooks still prescribe to the outdated Copernican theory of mediocrity, which states that our planet, our solar system, and our galaxy are not unique or special in any way. However, as previously described, our odds of even existing with the ability to support life are indeed unique. So is our sun.
The sun is a yellow dwarf classified as a G-2 (based on its mass and luminosity). It is among the 10% most massive stars in the galaxy, while most stars in the galaxy are red dwarfs (80%). Red dwarfs are not supportive to life for numerous reasons (and for word count sake, I won’t list them). Our sun has numerous characteristics that allow it to support us.
Firstly, it emits the right colors, a balance of red and blue light. It allows our atmosphere to build up the oxygen and the ozone layer, and protect us from a flood of UV radiation. Secondly, the sun is just massive enough to be on the main sequence (and not supernovae) long enough to support life and to maintain a steady fusion of hydrogen. Thirdly, the sun is metal-rich and has a plethora of heavy elements compared to other stars its age. The “sun’s metallicity may be near the golden mean for building Earth-size habitable terrestrial planets” (187). Additionally, the sun is highly stable, more so than most comparable stars. Its light output varies only slightly, preventing wild climate swings on Earth. Lastly, its orbit is more nearly circular than most stars its age, which helps to keep us away from the dangerous spiral arms of the outer galaxy. All of these things combined contribute to the life-supporting uniqueness of our sun.
Our Moon, the Best Supporting Actor
In 1993, it was discovered that the moon helps to stabilize the tilt of Earth’s axis, allowing for the seasons to come and go rather mildly. Without the slight pull of the moon’s gravity, the Earth could swing wildly, causing major life-threatening variations in weather and six months of incessant sun to one half of the planet and total darkness to the other. This is more than unpleasant; it would kill us.
Moreover, the moon contributes 60% to the regulation of ocean tides on Earth (while the sun contributes to the other 40%). Tides are key to spreading the wealth of nutrients from the continents to the oceans and circulate the heat within the ocean, which is necessary to keep the temperature of the higher latitudes mild. If it were slightly more massive, then the tides would be strong enough to slow down the Earth, elongating the days and knocking off our regulation of temperature between day and night.
The Earth, Powerful to the Core
In order to retain an atmosphere–which is necessary for the free exchange of the chemicals of life and to protect inhabitants from cosmic radiation–a planet must have a minimum mass. Additionally, it must have a minimum size to keep the core heat from being lost too quickly and a maximum size to keep the surface gravity in check to protect our mountains from crumbling. (Mountains are crucial to keeping us from having solely a smooth, water world in which no life could survive. Again, I will save the explanation for the sake of the word count).
Another totally unique and very important quality of the Earth is the system of plate tectonics. Plate tectonics refers to the interaction of rigid lithospheric plates that slowly move under the Earth’s mantle, creating the continents and mountains, and driving the Earth’s carbon dioxide-rock cycle which is critical in balancing the greenhouse gases to maintain the livable temperature of the planet. Plate tectonics are fueled by the internal heat generated by the radioactive breakdown of Potassium-40, Uranium-235 and 238, and Thorium-232.
Moreover, this decay drives the convection of the liquid iron surrounding the Earth’s core, creating the dynamo which generates the Earth’s magnetic field. This is crucial because it “shields us from low-energy cosmic rays [and…] solar wind particles [which] would directly interact with the upper atmosphere, stripping it away, especially the molecules of hydrogen and oxygen from water” (193-194).
Additionally, the Earth’s albedo–how much light it receives per area–helps to regulate the temperature of the Earth. Our oceans, polar ice caps, and continental interiors, including deserts, help to reflect some of the light from the sun and prevent us from taking in too much radiation. (That’s one reason that we should care about the melting of polar ice caps and glaciers).
All of this is uniquely Earth and makes it a perfect planet–the only planet–which can sustain life.
For more information…
Denton, M. Nature’s Destiny. New York: The Free Press, 1998.
Gonzalez, G., & Richards, J.W. The Privileged Planet. Washington, D.C.: Regenery, 2004.
Jastrow, R. God and the Astronomers. New York: W.W. Norton, 1992.
Sampson, P. Six Modern Myths. Downers Grove, Ill: InterVarsity, 2000.
Strobel, L. A Case for a Creator. Grand Rapids, MI: Zondervan, 2004.
Ward, P., & Brownlee, D. Rare Earth. New York: Copernicus, 2000.