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Brian Gregory is a down-to-Earth geosopher-geocientist. He earned a PhD in Geography and Environmental Studies from Carleton University, Ottawa, Canada in 2006, and has since been occupied with doing research with Canada's federal department of Natural Resources. In his spare time, he enjoys thinking and writing about complex topics in a simple and fun way. He is more 'exoteric' than 'esoteric' in his interests, and this is reflected in his writing. He also has a dry sense of humour, and is not offended by constructive critique.

The Biggest Puzzle about Life on Earth

Brian Gregory

Summary by ChatGPT: The essay by Brian Gregory explores the mysteries of evolution preceding the emergence of complex life on Earth, emphasizing the intertwined nature of geological, cosmological, and biological evolution. It discusses how catastrophic events sometimes propelled life's evolution, and delves into why it took about 4 billion years for conditions on Earth to become conducive for advanced life forms. The narrative also touches on recent discoveries that enrich our understanding of life's evolution and raise profound questions regarding the prerequisites for supporting life, not only on Earth but potentially elsewhere in the universe.

An Evolving Story

They say what doesn't kill you makes you stronger. That thought kept crossing my mind as I have been catching up with some of the the latest discoveries in evolutionary science. In spite of the many stops and starts, strange turns and catastrophic interruptions, the evolution of life on Earth has not only managed to keep going, but has become more complex, diverse and resilient against all odds. As astounding as this is itself, there is so much more to the story than what we have been taught in high school.

Before the turn of the millennium there were still some major things we did not know about the evolution of life and the history of our planet. To be fair, it was only a little more than thirty years since the theory of plate tectonics was officially validated and began to offer many new insights that firmly tied biological evolution with geological evolution of our planet. But an amazing number of new discoveries have been made since that time that add significant detail to evolutions' story.

While many questions still remain to be answered, it is remarkable how much of the puzzle has come together over that time. I will not go into great detail about these discoveries, for that would be way too much for this article, and there are some great books available for those who wish to dive deeper [1][2]. But I cannot help wonder how profound these discoveries are in helping to advance our appreciation for life's origins, on this planet or any other.

In this article, I want to focus not so much on the evolutionary history of life on Earth, but on some major events that happened with the evolution of our planet itself in order for it to reach a point where it could support life. Of particular interest is specifically how—as counter-intuitive as it seems—the evolution of life is so intricately tied to chaotic and often violent cosmological and geological cataclysmic events, which at times helped advance life, and at others nearly obliterated it. These recent discoveries have profound implications for how we think of our place in nature, how we deal the planetary scale issues we face today, and even more so, on a personal level , how we bring more awareness to the true nature of who and what we are.

So let's dive in!

Big Questions

For more than a hundred years or so, since Darwin's theory of evolution began to take hold in all aspects of natural science, we have become accustomed to thinking of evolution as a gradual, step-by-step process of increasing complexity of life forms, as if it advanced in a trajectory all on its own. For the most part, biologists and paleontologists have been able to map out the progression of various life forms in descriptive terms—mostly describing what life forms existed at various periods over geologic time. When all of these data are connected together, we get an undeniable evolutionary pattern. But deciphering how life evolved to take on the forms that they did at various times is a much more challenging process. Darwin got the ball rolling with the theory of natural selection, which for the most part still holds today, but it still only tells us a part of the whole story.

We know life started off as relatively simple stuff—as bacteria and other micro-organisms during the earliest periods of Earth history. But it took more than 4 billion years before the big explosion of life occurred at around 560 million years ago. That is when the party really started!

From that point on is when we began to see the full diversity of life as we know it. It is mindboggling to think that from that initial 4 billion years of nothing but bacteria emerged plants, fish, birds, large dinosaurs, strange animals, and more recently mammals, including our cousin primates and ourselves (homo sapiens). So think about this for a moment. Let it sink in. Every form of life that ever existed on Earth evolved from bacteria that took nearly 4 billion years to evolve!

A big question that comes to mind is why it took so long for life to really get going? Certainly, 560 million years was a heck of a long time ago (and almost impossible to comprehend for our human minds—see: Size Matters), but it is only a small fraction of the overall history of our planet. If we put all of geological time on a 24 hour clock, the big life party really only got going around 9:00 pm (21:00)—and we homo sapiens only showed up a few minutes before midnight! So what was the Earth doing all day? If life on Earth has a purpose, why would it not have happened much sooner?

As it turns out, purpose or no purpose, it took a tremendous amount of time for the Earth's environment to evolve to a point where it could support the advanced life we see today. While much of what we learn about evolution most often focuses on how life evolved during the last 560 million years, less attention has been given to the pre-conditions needed to support life in the first place. Thanks to new discoveries in cosmology and geology, the story now being told gives us a more complete picture of events. But it also raises some profound new questions!

From Hell to High Water

Overall, it took Earth about 4 billion years of its 4.6 billion year history to become suitable enough to support life as we know it today. There were many things that had to happen for those conditions to develop—many of which involved complex chemical reactions related to the generation of oxygen in our oceans and atmosphere, and to allow for photosynthesis to support plant life.

But enabling these chemical reactions required some major geological and cosmological events to happen in the first place—some of them being quite violent and catastrophic. It is this part that is so fascinating, which leads to more profound questions—both scientific and philosophical—not only about life on Earth, but about the possibilities for life elsewhere in the universe.

Before getting into those questions, let us take a look at some of these events using the help of the visual below. Visuals like this cannot do any justice to the real details of all that has happened, but it provides a visual guide for highlighting some of the major events that successively contribute to the development of our planets' life support system.

First, note the time scale on the left. It is marked by 1 billion year intervals from 0 (today, at the top) to about 5 billion years ago (at the bottom). We know the Earth is 4.6 billion years old, but that is only the official date of its formation. There was a period of time during the early stages of the formation of our solar system that we also need to consider. So for simplicity, we set the full timescale at about 5 billion years in total.

The big life party began about 560 million years ago—or about 0.5 billion years, as indicated by the box at the top of the time scale. Our Earth also began to look like it does today around this time, as the diagram shows the top three Earths all fit in the small box on the time scale on the left. There is no question that this period of Earth's history is the one that has drawn most attention. But the events we will focus on cover a much longer period of time (about 4 billion years) preceding the proliferation of life at the top of the diagram. The ability for the Earth to support life requires specific environmental conditions to develop. This took a HUGE amount of time, and some very strange events. So let us start at the beginning—(or perhaps, before the beginning).

Event 0—We Are Stardust!

Before we can begin to describe the formation of our planet and solar system, we need to understand how stars live and die. Stars form from two of the simplest elements H (hydrogen) and He (helium), and they burn as a result fusing together and fizzing apart of these elements releasing huge amounts of energy. The life of a star will last as long as this process continues. In the case of our Sun, it is estimated to have a lifespan of about 10 billion years. We are currently at about the half-way point, so it will be a long time before we lose our Sun to another a gigantic explosion (so there is nothing to worry about just yet)!

When stars die, they collapse under immense gravitational force. This causes the H and He to fuse creating heavier elements such as carbon, oxygen, nitrogen, iron, sulfur, nickel, silicon, aluminum, and many other elements that make up the periodic table [3]. After this fusion process, the star explodes and material made from all of these elements is blown into space and dispersed as stardust.

As was the case with our Sun, when stars form, they attract star dust left over from previous stars. Heavier elements (such as metals) will gravitate closer to the star, while lighter elements (such as gases) will remain at a further distance. This is why the four inner planets of our solar system (Mercury, Venus, Earth and Mars) are primarily rocky planets, and the outer planets (Jupiter, Saturn, Uranus and Neptune) are primarily gaseous planets.

Planets form from gradual gravitational attraction of material circulating around a newborn star under its gravitational force. Gradually, as matter differentiates and builds up at certain distances, larger bodies start to form and become more spherical under both the gravitational force of the star and the localized gravitational forces of the heavier matter.

What is particularly important at this stage is the specific combination of elements that happen to be present from the available stardust, because this is what determines the chemical composition of a planet and how it will evolve and change over time. Another essential requirement is such matter needs to be present within an orbital zone that is not too far (too cold) nor too close (too hot) to the Sun—otherwise known as a Goldilocks Zone. In terms of our own solar system and the formation of our planet, these initial conditions lead us to the first major event that makes our planet Earth so unique.

Event 1—Proto-Earth “Theia”

Did you know that before Earth formed, there was once a proto-planet called 'Theia'? I recall some speculation about this idea from my astronomy courses back in the 1980's, so it did not surprise me that there has been more development of this theory since that time. Basically, Theia was a proto-planet that was orbiting our Sun along with another somewhat smaller body in the same orbit—both within the Goldilocks Zone. The two eventually collided—quite violently! Theia became the Earth and the smaller body (or what was left of it) became our Moon. Earth won the battle due to its much larger size, and the Moon became trapped in the Earth's gravitational field. As much as it sounds like planetary warfare, this is basically how ended up with our Earth-Moon system.

There are some very critical elements to this part of the story that set the ball rolling for there to eventually allow for life to evolve on Earth. As mentioned earlier, it has to do with the mix of chemicals that just happened to be available to build the Earth and Moon. The fact that we ended up with the specific mix chemicals that we have is in itself a chance happening. This is especially the case for the mix of heavier elements such as Fe (iron) and Ni (nickel), and the many other rock forming minerals [3].

Unlike the Earth, the moon solidified and cooled fairly rapidly—partly because of its smaller size and partly its own specific rock chemistry. This is why we can still see so many craters on the Moon's surface. During this early period both the Earth and Moon were frequently bombarded by asteroids transecting our solar system. We do not see as many craters on Earth because its hot and molten surface at that time swallowed up most of the asteroids that collided with it obliterating impact craters, or occurred in places where the crustal rock was eventually recycled into the mantle.

Even more fascinating is how the Moon, also by chance, settled into an orbit that set the stage for eventual tidal influence on the Earth from its gravitational pull. Add to this the tilt of the Earth's axis ( its inclination) relative to its orbital plane with the Sun (and the Moon) that varies between 22.1 and 24.5 degrees every 40,000 years, and the additional periodic wobbling of its axis (its procession) that rotates like a top every 26,000 years, we have a complex intersection of gravitational forces that gives the Earth continuously changing orientation that results in an ever changing climate on its surface[4].

We will return to these parts further on in our story, but suffice to say, the formation of the Earth-Moon system, as it was then and is today, was in itself the result of a very specific combination of circumstances and chance happenings. The formation and orientation of the two bodies could have taken any number of alternative courses in terms of their size, composition, rotational periods, and gravitational forces. But for some reason (or no particular reason at all?) what happened—happened. And here we are today because of it. But it did not stop there.

Event 2—Hell on Earth

In geologic time, the earliest period of our planet is known as the Hadean period, derived from the Greek word Hades—meaning the underworld, or god of the underworld. The term is quite fitting because if there was ever hell on Earth, it was certainly very much like it during this time. The Earth was basically a sphere of hot molten rock with many very large active volcanos and frequent asteroid impacts. A place you would not want to be!

What is significant during this period is how the molten rock of our planet began to differentiate into layers—specifically into the core, mantle and crust [3]. As strange as it may seem, this was a key event for setting the stage for life conditions. The chemical composition and thermodynamic interaction between the core, mantle and crust will eventually lead to the development of plate tectonics, which provide the diversity of biogeochemical environments for life to thrive.

So we should be grateful that the development of the core, mantle and crust was one of the first things to happen in the growth of our planet. A change in the initial composition of elements available may have resulted in a very different structure to our planet, and life may have not evolved at all.

Event 3—Magnetic Appeal

An other significant event that occurred around this time is the development of a magnetic field surrounding the Earth generated by its metallic core. The fact that we have a core with a predominantly Fe composition to generate a magnetic field is in itself a chance happening. This again can be traced back to having just the right mix of chemical elements available from the beginning.

The significance this is life cannot survive long term exposure to UV radiation, and the magnetic field provides a shield to protect the Earth from harmful ultra-violet (UV) radiation from the Sun and other stars in our galaxy. Suffice to say, life would not stand much of a chance at evolving without good UV protection of the Earth's magnetism.

Event 4—Mantle Turmoil

The dynamic interaction between the Earth's core and mantle continued to develop through the early periods of our planets' history. As minerals and elements differentiated further, heavier elements sank to the center and added volume to the core, causing the composition of the mantle to become lighter. As the Earth continued to cool at surface, major temperature differences between the surface and the core led to the development of temperature gradients within the mantle that caused the mantle to churn in a way similar to water in a boiling pot. These mantle overturns caused very large blobs of lighter rock to rise to the surface creating thick pieces of continental crust. Thinner crust was created between these larger masses from volcanic activity which became oceanic crust, and eventually a system of plates formed driven by the underlying churning process within the mantle.

The surface environments that developed along with plate tectonics provided chemical and thermodynamic changes that promoted the advancement of RNA and DNA structures from simpler organic matter, and subsequent development of cyanobacteria in the oceans. The development of cyanobacteria was a crucial event in itself, as its chemical interactions with ancient ocean water began the production of greater amounts of oxygen in our oceans and atmosphere.

None of this would have occurred were it not for the specific chemical composition and thermodynamic activity within the Earth's mantle. Differences in either the initial composition of the Earth or heat distribution mechanisms inside the core and mantle could have resulted in a very different crustal surface. But once again, it did not stop there. The evolving plate tectonic system brought about even more profound changes to the surface of our planet!

Event 5—Come Together!

The influence of plate tectonics on the development of the Earth's life support system did not stop with mantel overturns. Increased plate tectonic activity over time promoted the growth of additional continental landmass and larger ocean areas and oceanic crust. At various time periods, super-continents formed when all continental landmasses came together. Some of the oldest, such as Nuna, date back to 2 billion years, and the most recent was Pangaea which occurred about 300 million years ago. But they did not just stay that way. For at least the last 2 billion years, the global tectonic system has driven cycles of continents coming together and drifting apart.

So why is this important for life? Well, one thing we know about life is that it evolves and adapts to changing environmental conditions. As plate tectonics developed continental landmass in some areas and oceanic masses in others, a wide diversity of environments developed around the globe. Different forms of life are forced to adapt in different ways when subject to changes in environmental conditions. These environments varied greatly due not only to differences in landmass and ocean composition, but also different climate systems related to the continuously variable motion of the Earth relative to the Sun as described above[4].

Of course this is all happening over very long periods of geologic time. The periods of continents coming together resulted in cross-breeding of species, and the periods of breaking apart resulted in further diversification of species evolving in new environments.

So we can see how these major events contribute to setting the stage for the Earth's life support system, and it is fascinating to learn that all of these discoveries were made only within the last 50 years. But that's not all!

These major events did not progress without some complications. There were, and continue to be, other seemingly random events that have paradoxically had significant negative impacts on the Earth's evolving life support system, while at the same time giving life a boost!

Hell Freezes Over—(And Other Disturbing Events)

For those who ever wonder about Hell on Earth, we know it already happened in the very beginning. And for those who wonder about Hell Freezing Over, that has already happened too! Approximately 2.3 billion years ago, and again about 700 million years ago, our entire planet was completely frozen over resulting in a prolonged period of global glaciation called Snowball Earth. There are still some debate as to the cause of these global glacial periods, but evidence increasingly points to large scale cosmological causes.

One theory suggests Snowball Earth was the result of our Milky Way galaxy colliding with another smaller (dwarf) galaxy, while others point to evidence of our solar system periodically passing through more dense arms of our Milky Way galaxy [5]. In either case, the Earth was exposed to a substantial increase in cosmic radiation—much more than what our magnetic field could normally handle.

This radiation caused ionic nucleation of particles in our atmosphere that resulted in thick dense cloud cover. This in turn led to global freezing and the entire Earth being covered in snow and ice. A major consequence of this event was extensive build-up of bacteria in our oceans up to that time nearly became extinct. So imagine after 2 billion years of evolution of life to have it almost entirely wiped out by a collision of our solar system within our own galaxy!

Thankfully, all was not lost. As I mentioned in the opening of this article how what doesn't kill you makes you stronger—this event that nearly entirely wiped out life on Earth paradoxically made a significant contribution to its evolutionary progress. Once the Earth warmed up again, the smaller proportion of bacteria that survived responded by developing new protective layers drawing from a build up of phosphorus in the oceans. This enabled life to evolve from the simplest cells without any nucleus or protective shell (called Eukaryotes) to cells with a nucleus and a protective shell (called prokaryotes), and then on to multi-cellular organisms. This was one of the first major steps in the evolution of complexity in life and one upon which all other life forms that followed are built.

If that was not enough, there have been other major events that were not as catastrophic, but certainly set the path of evolution back a few steps from time to time. These mostly include less severe glacial periods (commonly related to Milankovitch cycles [4]), periods of increased volcanic activity, and let's not forget about major asteroid impacts.

The break points in the geologic time scale [6] are marked by many periods of both minor and mass extinctions due to one type of catastrophic event or another, or some combination that resulted in sudden changes to the Earth's environment. When such events happen, there may be many extinctions, but life always manages to push forward by adapting to new environments [7].

It is another one of those paradoxes of nature—that being, although the Earth's life support system is delicate and highly vulnerable to sudden changes, life itself seems to be incredibly resilient no matter what it is subjected to—always pushing on and evolving into new forms adaptable to new levels of complexity. As mind-boggling as all of this this may seem, the sequence of events that allowed for the evolution of life on Earth leave us with even more profound questions.

Against All Odds?

Whenever I am asked if I could spend an afternoon with anyone from history, my answer is Albert Einstein. I would be humbled by the opportunity to speak with such an intellect, but it would also be his humbleness, sense of humour and wisdom that would make the experience most worthwhile.

There are many topics I would like to discuss with him, including a wide range of questions relating to what we covered above. Einstein passed away in 1955, about 15 years before plate tectonics was officially adopted, and before we began putting all of these pieces of the evolutionary puzzle together. I would be interested in knowing his thoughts on these more recent discoveries.

There are many implications for how we think of our place in nature with these recent discoveries, such as our current dilemma with climate change, our impact as a species on other species of the planet, and its global ecology, or perhaps where we home sapiens fit within the big scheme of things. Those are all questions I hope to explore in other articles. But the one major question I would like to discuss with Einstein is, given all of these more recent discoveries and a much more coherent picture of how things evolved on Earth, if he still thinks “God does not play dice with the universe!” [8],[9].

Einstein's comment was made at a pivotal time in 20th century physics. The laws of physics of the universe were seen as deterministic and predictable up to that point, until discoveries made in quantum mechanics suggested the contrary—that things exist as a result of chance and probability, and not on the basis of any pre-determined set of laws.

Although Einstein's comment was a reaction to discoveries of made about the quantum level of the universe, the same dilemma applies in the case of evolution. Just as the laws of physics emerge from a realm that is governed by chance, so too it seems that the evolution of life is fundamentally dependent on chance happenings. Even if life itself exhibits some form of determinism (in which I think it does)—there would not be any life at all if it were not for these seemingly random and chaotic events that came together and built the stage upon where life could evolve.

One profound question is—how can we expect life to occur in the universe, if the conditions required to support life are subject to such rare chance happenings? And similarly, if the major events described above that led to the evolution and development of the Earth's life support system all occurred as a result of chance, what is the probability of all of these events happening in a chain-like fashion anywhere in the universe?

I presume if we ask a team of the worlds' greatest mathematicians to solve this problem, I am highly doubtful that such a calculation is anywhere near possible. I am not sure what the answer is, or where they would start. But it might be helpful to think of it as analogous to winning a lottery like 6/49 [10].

In 6/49, a player selects 6 numbers between the values of 1–49. The chance of selecting one matching number is about 1 in 10 (or 0.10), and the chance of selecting two matching numbers is about 1 in 80 (or 0.012). The probability of selecting more matching numbers greatly diminishes to about 1 in 14,000,000 (or 0.000007) for selecting all six matching numbers. At first glance, selecting 6 matching numbers seems quite feasible, but the trick is that the probabilities are successively conditional—each one dependent upon selecting the others.

The same situation applies here. Each major event is conditionally dependent upon the previous event happening successfully. The successive probabilities of all of these events happening in the sequence that they did—when combined—would be infinitesimally small! What ever that value might be, it would likely be a value with so many zeros after the decimal it would run off the end of this page—so small, that such a value would normally be considered impossible.

But here is the twist! In the case of a 6/49 lottery, although the probability of any particular player winning is extremely small, there is a 100% probability that someone somewhere will win the jackpot! The same principle would apply to the events that led up to the Earth having a life support system—although the probability of it happening is infinitesimally small, in a universe of infinite possibilities, there is a 100% chance of it happening somewhere at some point in time! And it did—and we, and all other life on this planet, are here because of it. So let us count our lucky stars, eh?

So the BIG question is—what if God does play dice with the universe? And if he does, who are we to argue? Perhaps he set the universe in motion not knowing what the exact outcome will be, only knowing that he will win the jackpot at some point? I wonder what Einstein would think, and if this type of universe makes any kind of sense. Moreover, what implications does this have for more existential questions—religious or otherwise? There are no easy answers to these questions, but they certainly open up new areas for deeper contemplation.

One thing is for certain though, given all of the very delicate processes and chance happenings that occurred to put life on this planet, we can be sure that life on Earth is indeed a very rare thing, and all the more reason for us to take proper care of it and celebrate it. These discoveries offer us an opportunity to develop an even deeper appreciation of what it really took for life to evolve on our planet. It instills a sense of wonder and awe profound enough to bring us to our knees.

Epilogue

Those who ever have the opportunity to experience the Auroras Borealis or Australis should take the opportunity to show a deep sense of gratitude. They form as a result of solar particles interacting with the magnetic field of the Earth [11]. These lights have been dancing for nearly 4 billion years now—displaying quite vividly to us the protective shield our planet made to allow us to be here. Beyond the amazing science of it all—it is a divine work of art, and a celebration of the mysteriousness and wonder of the universe in which we live, and the precariousness of our existence.

Links and References:

[1]Nick Lane, 2002. Oxygen: The Molecule that Made the World. Oxford University Press.

[2] David Christian, 2018. Origin Story: A Big History of Everything. Little, Brown Spark publishing, New York.

[3] A brief overview of the structure and composition of the Earth: "Earth's layers: Exploring our planet inside and out"

[4] See: Instructive video on Milankovitch Cycles

[5] See: "Astro Seminar: Christopher Purcell (West Virginia University)" Or: "Snowball Earth events driven by starbursts of the Milky Way Galaxy"

[6] See: Official Geologic Time Scale of the GSA.

[7] See: Six Mass Extinctions.

[8] See: "What Einstein meant by 'God does not play dice'"

[9] It is worth noting that Einstein is referring to 'God' as the true nature of the universe, whatever that may be, and not necessarily a religious or imaginary God separate from our reality and universe. This is a complex subject—something I hope to explore in another article.

[10] See: "Lotto 6/49"

[11] "What are the northern lights?"