The Fortuitous Planet

Why humanity is lucky to be here

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If we could explore the planets of the distant universe, what would we find on them? Would we encounter dead rocks floating in the abyss, or planets teeming with life? Would we need to confront life that is more advanced than us? Or is the universe filled with ruins, like Rome or Greece today, of complex civilizations that have long since perished? The history of the universe suggests that indeed, our existence as sentient molecules on this planet is fortuitous and something to be appreciated and safeguarded.

To the best of our knowledge, the universe began some 13.8 billion years ago with the ‘Big Bang.’ Before that moment, per our current understanding at least, nothing existed. Everything that would ever be, was compressed into an unimaginably small space, a ‘gravitational singularity’ far smaller than an atom. So dense, in fact, that it infinitely curved space-time such that the concept of time didn’t even exist. Within the singularity, the four fundamental forces we know today (the weak nuclear force, electromagnetism, strong nuclear force, and gravity) were equivalent in strength and probably unified into a single fundamental force.  

This singularity suddenly and inexplicably burst outward. In the first second of the universe’s existence, the concepts we call time, space, and the laws of physics emerged. In the following seconds, subatomic particles (quarks, electrons, neutrinos…etc) began to form, then larger particles like positively charged protons. Neutrons were formed by the collision of negatively charged electrons and protons under these extreme conditions. By about 3 minutes after birth, the universe had cooled just enough to allow those larger particles to fuse, creating the first simple nuclei, the cores of hydrogen and helium atoms.

After about 20 minutes, the nascent universe was no longer hot enough to sustain fusion, leaving a hot and expanding soup of electrons, hydrogen, and helium nuclei. The opaque plasma soup continued expanding and cooling for about 300 thousand years. At this point, it had finally cooled enough to allow early hydrogen and helium nuclei to capture electrons, neutralizing their charge and making the universe transparent to light for the first time. Despite this, the universe remains a completely dark “fog,” with no stars yet formed to give off light.

Everything remained in total darkness for another 150 million years until minute imperfections and irregularities in matter density allowed gravity to pull atoms together into clumps. As these gases pulled together, they began to collapse under their gravity, becoming hot enough to restart the fusion process of the early universe. When this happened, it ignited the very first stars; light had finally come. These early stars were 100 times the mass of our Sun, dying quickly and exploding into supernovas that scattered matter across a growing universe. That matter formed the basis of new, smaller stars over the next few hundred million years; furnaces that would produce more complex and heavier elements, like iron, nickel, and carbon. It was around this time that stars gathered together in rotating spiral formations that we now call galaxies. 

It would be about 9 billion years after the Big Bang before our Sun and Solar System began to form. The Sun gobbled up most of the matter, leaving just a spinning disk of debris around it. Clumps of this debris would pull together and become the planets. These early proto-planets competed with one another for slots around the new star. The early Solar system was violent, with frequent impacts between objects, ranging from specks of dust to collisions between the proto-planets themselves. Our Moon is thought to have formed when a Mars-sized planet collided with an early Earth, ejecting a significant portion of our own planet into orbit.

We know this because exploration of the Moon has retrieved rocks for study. From the Moon’s mantle, Basaltic rocks are eerily similar to those from the Earth. Oxygen isotopes sealed into those rocks also closely match terrestrial counterparts, far too precisely to be a coincidence. Yet, the scale of such a collision and the breathtaking sight it must have been is beyond comprehension…it is too bad no one was around to witness it.

A Fortuitous Planet

There is nothing particularly special about the Earth or the Solar System. We now know that there are tens of billions of planets like the Earth in the universe. Yet, I argue that our placement on this planet is still fortuitous. Earth sits in the middle of the Sun’s so-called “habitable zone” where temperatures are ‘just right’ for the formation of liquid water, a prerequisite for life as we know it. Also, from its inception, Earth had access to heavier elements born of extinct stars, namely carbon.

All life on Earth is carbon-based, which itself is a probabilistic consequence of the characteristics of carbon itself. Carbon readily bonds with itself and other elements, allowing the formation of complex molecules including DNA and proteins. This is because carbon has 4 valence electrons and is uniquely able to form strong, yet pliable bonds with other elements; perfect for life which must maintain enough structure to counter entropy, but be adaptable enough to evolve, grow, and change.

Also, unlike Venus, Mars, or Mercury, Earth has a powerful magnetosphere that shields us from Solar wind. Without it, our atmosphere would be eroded by the Sun, and life would be constantly exposed to harmful radiation. It is difficult to comprehend just how many variables on Earth came together at just the right time to form and sustain life. Even if these conditions are ultimately only temporary.

Today, we humans may also feel fortunate that the mass of our planet does not trap us on the surface. Already, our rockets are pressing upon the limits of physics to escape Earth's gravity, using over 95 percent of their mass to reach orbit, with only five percent (at best) left for a useful payload. Had the Earth been more massive, it would be vastly more difficult, if not outright impossible, for us to explore space.

We might also feel fortunate for the placement of our Moon. Rich in water and Earthly elements due to its shared history, the Moon is distant enough from Earth that it poses no risk to life, but close enough that it could serve as a proving ground for human planetary exploration, or a proverbial “gas station” for a refuel on the way to Mars or other locations in the Solar System. None of the rocky planets orbiting the Sun can claim a Moon remotely like ours. 

In an astronomical sense, it didn’t take very long at all for life to emerge on this fortuitous early Earth. There are likely countless planets in the universe, a fraction of those probably are, or were, located sufficiently for the formation of life, either carbon-based or otherwise. Nonetheless, the pale blue dot is more fortunate than most. Next, we examine how and why life may have sprung from lifeless matter.

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