© Darius A Irani, 2023
EATING THE WHOLE DAMN FRUIT SALAD.
Most of us have no idea of the specific events that had to occur in just the right sequence over the last 4 billion years before complex life could emerge on our planet. Could the same sequence have happened somewhere else - possibly. When one is dealing with billions of galaxies each with billions of stars, to claim uniqueness would be hubris. However, the odds of us reaching such a planet are very small even if we could predict where it would be when we finish our journey. The distances are so vast and our technology so primitive, that it would take thousands of years just to exit the Oort Cloud at the very edge of our solar system. No electromechanical devices could function for even a minute fraction of the duration of the journey, the spaceship would only be able to transport a few dozen earthlings, and the generation that started the journey would be old before they even got to Neptune. There is no Plan B. This beautiful blue orb is all we have. If we destroy it, everything we have done and accomplished will be destroyed with it. Maybe, just maybe, if we understand the odds that Nature had to overcome to bring it all together, we might better appreciate the gift of life we have been given. We might even realize that our ideologies, religions, wealth, power and all the other stupid things we fight over are meaningless. The ONLY thing that matters is preserving our spaceship home.
Useful Information
A mile (or Kilometer) is too small a unit to measure inter-planetary distances within our Solar system. On the other hand, a Light-year is more suitable for measuring interstellar distances, but too large for inter-planetary gaps. Consequently, astronomers have identified an intermediary unit of length for measuring distances within the solar system – The Astronomical Unit (AU). The Earth’s orbit is almost circular with a radius averaging about 93 million miles (about 149 million km). The difference in the radii between perihelion and aphelion is only about 3.16 million miles. This average radius of 93 million miles is the dimension of an AU. The closest planet to the Sun is Mercury with an orbital radius of only 0.387 AU, and furthest is Neptune at about 30 AU. At the furthermost reaches of our solar system is the Oort cloud at a staggering 5,000 to 10,000 AU
Almost all life on our planet is inextricably tied to water and oxygen. The appearance of these two substances represents significant turning points in the emergence and evolution of complex organisms on the planet’s surface. Consequently, as we explore our origins, these two substances are on the top of the list for prerequisites. Can life exist without Oxygen? Yes, it can. There are simple organisms that get their energy from Sulphur and not Oxygen. However, these are very primitive organisms. Very few of these are multicellular, and none comprise more than a dozen or so cells.
Location is Everything
All stars have a defined orbital area called the habitable zone (HZ). Within this zone it is not too hot or too cold and a planet can sustain water on its surface. For any given star, the distance of this zone from the star, and its extent depends on the size and luminosity of the star. An orbit closer than the HZ would result in high surface temperatures and water would be lost by heat and the greenhouse effect. Incoming infrared radiation would be trapped, and the water would boil away. At greater distances, the greenhouse effect would be inadequate to prevent the water from freezing. Within our solar system Earth is the only planet within this zone. Mercury and Venus are too close to the Sun, and Mars together with all the outer gas giants are outside this zone. We are barely in it!
Sol’s habitable zone stretches from 0.9 AU to 1.5AU. Some estimates suggest that the inner boundary may be 0.95 AU or even 0.99 AU. Thus, we are right on the brink of being too hot to hold any water. This makes our headlong rush towards global warming an even greater act of insanity. If we were just 2.5 million miles closer to the sun, life would not exist. Be that as it may, the Earth came together as a planet at just the right distance from the sun and here we are.
Size Matters
Large stars have life spans measured in just millions of years. Complex life on Earth took about 3 billion years to emerge. Consequently, had our Sun been much larger, the Earth would not have had enough time for life to emerge and evolve into the diversity and complexity we see around us.
Very small stars (red dwarfs) pose their own limitations. They are much cooler than the sun, so their habitable zone is much closer and narrower. The immediate consequence is that any planet in the HZ would be tidally locked to the star, preventing it from rotating. One half would always face the star and the other would be in perpetual darkness - just like our moon. Life on such a planet would be both different and unpleasant. For starters, these small stars emit mainly Infra-Red radiation, so on the star side vision would have evolved to work in this wavelength. Whereas the other side would have adapted for almost total darkness. Yet again we beat the odds and got a star that was the right distance away and would give us heat and energy for 10 billion years. Now all we needed was Oxygen.
Cyanobacteria Save the Day
The air we breathe is composed of 78.09% Nitrogen, 20.95% Oxygen, 0.93% Argon, 0.039% Carbon dioxide and traces of other gases. It was not always so. In the beginning - 4.6 billion years ago – our atmosphere was composed of Methane, Hydrogen Sulfide, and much Carbon Dioxide, but no Oxygen. Primitive microbes were present, living anaerobically on Sulfate. The surface of our planet must have been a desolate landscape. Almost Lunar in appearance, bereft of plant or animal life. Six hundred million years later the oceans had formed, but there was still no Oxygen in the atmosphere. If it were not for the Cyanobacteria, this would have been the end of the story. Strictly speaking, there would have been no story at all because there would be no one to write it.
Fossils of Cyanobacteria date back 3.5 billion years making them just about the oldest living things on our planet. They are still the largest and most important group of bacteria. They produce Oxygen as a byproduct of photosynthesis and are responsible for the original presence of Oxygen in our atmosphere. Oxygen, however, is a very clingy element. It easily bonds to other elements e.g., Iron to form rust. So, in the early stages, whatever Oxygen was produced in the atmosphere would quickly be absorbed by the so called “sink” elements like Iron.
Finally, about 2.33 billion years ago a small amount of Oxygen made a permanent presence in the atmosphere. This was the start of a rapid but not understood increase in atmospheric Oxygen. Scientists call this period the GOE (Great Oxygenation Event). At the end of the GOE the atmosphere contained enough Oxygen to support multicellular life, which is a prerequisite for complex organisms to evolve. The stage was now set. Nature had beat the odds and won the trifecta. We had the right star, a good orbit, plenty of water and Oxygen. Things would crawl out of the oceans and stay. Evolution would do the rest, and our species would be given the gift of life.
A Second Eden
Fast forward a few hundred million years to the middle of the eighteenth century. The quality of life for humans was not very good (that is another story) but the planet was in great shape. Humans had long ago invented agriculture and we had enough room to feed the then world population of about 800 million. Knowledge of medicine and disease was still very primitive, so life expectancy was shortish. But the planet teemed with flora and fauna. So much so, that several scientists were beginning to theorize why this might be, eventually resulting in the theory of evolution. We were just about to start exterminating other living creatures, so the bison herds and plains Indians and a host of other species were blissfully unaware of the fate that awaited them. It almost looked like the garden of Eden resurrected once more. If our planet could feel rueful about itself, it would call those the ‘good old days.’
Then two turning points changed everything. These were the start of the two industrial revolutions, and a series of explosive increases in our population. Although they did have some harmful socio-economic effects on humans, by and large the industrial revolutions would herald two centuries of intellectual advancement for our civilization. Sadly, this came at a huge cost to our environment. Both the industrial revolutions were fueled by combustion. The first by external combustion in the form of steam engines, and the second by the more familiar internal combustion engines. Every car we drive, every electrical switch we turn on, every tap that delivers water to our homes, every stocked shelf in a grocery store, every power tool we use, almost everything we take for granted is only possible because somewhere combustion provided energy, but it also produced CO2. Even every breath we take adds to the CO2 in our atmosphere.
CO2 is not the most efficient greenhouse gas. Luckily, the others are only present in trace quantities. CO2 itself comprises barely .04% of our atmosphere, but its effect is way out of proportion to its volume. The evidence suggests that historically, CO2 remained at a steady level for thousands of years. Then starting in the mid-eighteenth century – coinciding with the start of the industrial revolution - its level gradually increased until now it is 50% greater than that historical baseline.
Nature is very clever. From the start it realized that the level of CO2 had to be contained, and Oxygen had to be regenerated. So, it created a huge sink for the gas. Whereas most fauna absorb oxygen for energy and dump CO2 as waste, flora do the exact opposite. Via Photosynthesis, plants (and other organisms in the oceans) absorb CO2, extract carbon for energy and dump oxygen as their waste. A perfectly balanced duality that even yin and yang would be proud of. A balance that survived for thousands of years until our greed and sheer numbers overwhelmed it. Between destroying our forests, polluting our oceans and using combustion to provide our ever-increasing energy needs, the planet can no longer replenish the amount of Oxygen we are consuming. This may not affect our generation, or the next hundred generations, but one day it will kill what is left of us.
Eating the whole damn fruit salad
Mankind's earliest records date back to about 10,000 BCE. So, it is probably safe to suggest that it took about 11,750 years for the human population to get to 800 million in 1750. By 1900, just 150 years later it had doubled to 1.6 billion. Then we had a century of war, despair and genocide which would cost over 300 million lives. You would think this would have slowed us down. Far from it, our population increased fivefold to over 8 billion. If we superimpose the graph of our population growth on top of the change in CO2 levels, the correlation is undeniable. Our numbers are killing us, but we do not seem to care.
Rumor has it that when there were just two of us, we were very naughty and took a measly little bite from an apple. For this minor misdemeanor we were evicted from the first Eden. Now that there are 8 billion of us, we appear to be retaliating by eating the whole damn fruit salad, and screwing Eden while we are at it!
