Earth Is “Just Right” for Life

Earth was created millions of years ago by the same process that formed the rest of the known universe, yet it is set apart from the other planets by its ability to harbor life. It is known as the “Goldilocks Planet,” in reference to the popular fairy tale, for having just the right characteristics for life to exist. Earth developed these characteristics during its formation from the solar nebula that became our solar system. Its position relative to the Sun significantly impacted its formation and evolution, whereas other planets, such as Jupiter, from the same nebula remained inhospitable to life.

In addition, Earth’s structure makes it habitable in comparison to a high-pressure gas giant like Jupiter. Finally, the composition of the atmosphere and mass of Earth makes it possible for life to exist, unlike Jupiter’s which lack an abundance of the key ingredients for life. Discovering other Goldilocks planets, through missions such as the Kepler mission, could provide alternative habitats in case Earth becomes uninhabitable.

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Further, studying if and how life developed on those planets would have far-reaching consequences. Earth is known as the Goldilocks Planet because its formation, location, structure, and composition made it suitable for life, unlike other planets in our solar system such as Jupiter.

The Formation of Our Solar System

When considering how Earth became the perfect planet for life, it is necessary to look at its formation. The Big Bang spewed millions of sub-atomic particles into the universe, which cooled and clumped into larger bodies over the course of millions of years.

One of these extremely hot balls of gas, called a solar nebula, caved in on itself and spun so quickly that it flattened into a disk-like shape. The centrifugal force from the spinning drove most of the gas to the middle, forming the Sun. The rest of the mass was clumped into smaller planetesimals through a process called accretion. The Sun’s energy warmed the planetesimals nearest it so that lightweight volatiles such as water were pushed towards the outer planetesimals, leaving only the densest materials.

The outer planetesimals grew into giant planets relatively quickly when the ice condensed on the denser space debris that was already adding to those growing planets’ masses. These outer planets became so large that they affected each other’s orbits, causing collisions to occur more frequently. The inner region of the solar system became the four terrestrial planets, including Earth, and the outer region was eventually left with the four larger Jovian planets, including Jupiter. As a result of the material available for each planet to grow from, especially iron, and its protective magnetism, Earth became the densest planet in the solar system and Jupiter is much less dense.

The Locations of Earth and Jupiter. The location of Earth is another characteristic that makes life possible. Earth orbits the Sun, which is found at the center of our solar system. Comets and asteroids pulled towards Earth by its gravitational force eventually covered most of Earth’s surface with water, and the Sun allowed it to remain in a liquid form.  As Earth evolved and millions of life forms developed in its oceans and eventually on land, the Sun supplied the Earth with energy for life. Without the Sun, life would not have been possible on Earth.  Although the energy of the Sun also reaches Jupiter, this gas giant has such extreme pressures underneath its clouds that human life on Jupiter is impossible, and other life is very unlikely to exist.

The Structures of Earth and Jupiter. Earth has three main layers that were composed from the dense materials from the nebula, with the outermost layer being the crust. The crust that makes up the ocean floor is made primarily of basalt while the crust that makes up the land is composed of granite. The mantle, the thickest layer, lies below the crust. No parts of the mantle are liquid, even though its temperature increases as it gets closer to Earth’s core. The core of Earth lies in the very center of the planet. The outer core is liquid while the inner core is solid. On the other hand, Jupiter is mostly composed of clouds of the lighter gases from the original solar nebula. This gas is compressed under very high temperatures deep within the planet until it becomes a liquid.

The planet’s rotation combined with the high pressure on the liquid hydrogen causes Jupiter to emit a strong magnetic field. Scientists also believe that Jupiter may have a solid core or a core made of liquid hydrogen with a high viscosity.  The Compositions of Earth and Jupiter. Earth and Jupiter’s atmospheric compositions and their availabilities of carbon and water allowed only the former to become hospitable to life. Earth and Jupiter have very different atmospheres. More than three quarters of Earth’s atmosphere is made of nitrogen. Just over 20% of its atmosphere is oxygen while the rest is composed of various trace gases. In addition, Earth’s ozone layer protects living things from most of the Sun’s harmful UV radiation.

On the other hand, Jupiter’s atmosphere is mostly composed of hydrogen and helium like the Sun. It is held together under such a high pressure that it is very hot and would be possibly hospitable to only the most resilient of life. In addition, Earth has an abundance of the element, carbon. Carbon is extremely important because it is necessary for life. Its four valence electrons allow it to bond very easily and create many compounds, such as macromolecules, that are necessary for living things. For example, nucleic acids, which make up the genetic code of all living things, contain carbon.

Therefore, living things would not be able to reproduce or exist in the first place without this element. During the Galileo probe’s mission to Jupiter in 1995, only traces of carbon were detected in Jupiter’s clouds, which would not be able to sustain life.  Finally, life needs more than simply the presence of carbon and a friendly atmosphere to exist. Most of Earth’s surface is covered in water, a compound that all living things need. On the other hand, the Galileo probe was only able to find traces of water in Jupiter’s clouds. Earth’s protective, oxygen-rich atmosphere combined with its abundance of carbon and water allow it to foster life unlike Jupiter’s high-pressured atmosphere and sparse availability of carbon and water.

Conclusion

Since we know the characteristics that have allowed our planet to become the “Goldilocks” for life, it is possible to search for other planets like it in the universe. The Kepler mission, which recently ended, was used to search for exoplanets outside of our solar system. By comparing the formation, structure, location, and composition of these new planets to Earth, it is possible to find another planet that can support life. This is important because it could provide a good habitat for life in case Earth becomes uninhabitable. In addition, it is interesting to know if there is already life on other planets and how it has developed.