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Five billion years ago, a cloud of hydrogen and dust from long-gone, exploded stars began collapsing under the pull of its own gravity. When enough had gathered together, the pressure of all that material on its core ignited nuclear fusion, and our tiny Sun was born.

Four and a half billion years ago, Earth and hundreds of other tiny planets were coalescing from the remaining debris of that cloud. Some of those planets would be absorbed by Earth, some by other planets, and much would also be ejected away from the Sun into deep space. Late in the process, another planet crashed into Earth, and out of the wreckage came our Moon. It was originally much closer to us, but over time it traded its inertia with Earth’s rotation, slowing down our days as it moved further and further away.

Four billion years ago, our planet had cooled enough to have a solid crust, and an ocean of water condensed on its surface. Earth had grown to just the right size, large enough to hold an atmosphere, with just enough radioactivity to keep its interior hot and rotating. This spinning core created a magnetic field around the planet, protecting the atmosphere from the worst of the Sun’s radiation. Poor Mars was too small and cooled too fast to keeps its liquid core, so its atmosphere was slowly stripped away by the solar wind.

(more below the Orange Spaghetti Monster)

Three and a half billion years ago, life had gained a toehold on Earth. Complex polymers were self-replicating, competing for useful molecules in the chemical soup of our oceans. Evolution of those polymers began, as those which could replicate the fastest began to dominate. Of the thousands of possible precursor molecules, only twenty amino acids and a handful of nucleic acids came to dominate the composition of life. Some of these became encapsulated in membranes of lipids, concentrating their activity. Some combinations of these proteins and nucleic acids and lipid membranes were much more effective at replicating; these grew faster and broke their cells in half as they grew too large and unstable, over and over again. The living first cells had been created.

Three billion years ago, the chemistry within the cells had become complex enough to begin producing oxygen as a byproduct of photosynthesis. This was a huge evolutionary advantage – life’s chemistry could now be powered by the Sun. It also changed the planet. At first the by-product oxygen was absorbed by the oceans and the metals of the sea bed. Then it bubbled out into the atmosphere, rusting the land and converting the methane atmosphere to carbon dioxide.

Two and a half billion years ago, the Earth’s methane was being eradicated. Most of those life forms that had evolved to live in a methane-rich atmosphere died in the new oxygen-rich atmosphere. However, our younger, cooler Sun could not keep the atmosphere warm enough without a thick layer of methane. The Earth froze over, perhaps entirely, for three hundred million years while life continued evolving in the oceans.

Two billion years ago, the earth had again warmed, and the abundance of cellular life exploded. As these cells interacted with each other, eating and absorbing each other, they became more complex. A new type of cell evolved, with a true nucleus to store much of its genetic information. Bacteria and eukaryotes would continue to co-evolve, but the advantages of complexity and specialization now resided with the eukaryotes. All animals and plants with specialized cell types would evolve from cells with a nucleus.

One and a quarter billion years ago, the first multi-cellular creatures evolved. Life had figured out how to control gene expression in ways that allowed cells with identical genetic information to function differently and yet still cooperate to better survive. This also led to the first organisms capable of sexual reproduction. Sex was a huge advantage for both life’s diversity and the preservation of genes, as genetic information could be exchanged and recombined at a much faster rate while still preserving what worked.

One billion years ago, a period of massive climate changes wracked the Earth. It froze up and reheated on multiple occasions, tens of millions of years at a time. These events were largely based on the drift of the continents from the south pole to the equator and back again, and the volcanos formed by these movements. Each period killed off much of the life, but also encouraged more specialization and optimization.

Five hundred million years ago, Earth defrosted for the last time. Lesser ice ages would come and go, but never again would the planet be completely covered by ice. In addition, there was now enough oxygen in the atmosphere to form an ozone layer. With the sky now able to protect the land from the Sun’s ultraviolet radiation, just as the seas had always done, life began to move onshore. Larger, ever-more-complicated animals swam through the seas, eating each other, mating with each other, and co-evolving with each other. The first animals with backbones evolved, a feature with massive advantages for evolution and adaption.

Two hundred and fifty million years ago, another series of massive climate changes killed off most of the marine life and much of the terrestrial life. As the world recovered, dinosaurs and the first mammals evolved from the survivors.

Sixty-five million years ago, the dinosaurs were wiped out by a meteor impact and its resulting climate change. The mighty T-Rex had evolved less than five million years previous to the impact, the culmination of 185,000,000 years of evolution since the dinosaurs first appeared. Their loss was the mammals gain, as the new world established a cooler temperature than that which had favored the dinosaurs.

Seven million years ago, the first Hominids evolved.

Three hundred thousand years ago, the first homo sapiens evolved. The earliest human burial we have found is ninety thousand years old, indicating that we may have begun thinking in religious terms by then. Thirty thousand years ago, we were carving images of an earth mother throughout much of the world, perhaps indicating the first widespread religion.

Twelve thousand years ago, we began to build towns based around agriculture.
Ten thousand years ago, the last Ice Age ended. Man had crossed the Pacific to settle in North America, resulting in the extinction of much of the large wildlife that had evolved without humans. Dogs were becoming fully domesticated, having co-evolved with migrant humans for a hundred thousand years.

Five thousand years ago, humans were building our first cities. The Sumerians began writing, creating a new way to communicate that allowed information to be stored beyond the lives of men. There were roughly 14,000,000 humans on Earth, or almost the population of Pennsylvania.

Four thousand years ago, Egyptians were building pyramids, China had formed its first dynasty, and the Indus civilization was growing along the river for which it is named. Hammurabi created his code of laws. The horse was domesticated, humanity’s first great success in using energy beyond its own for transportation and work.

Three thousand years ago, the Zhou Dynasty began in China, the Kingdom of Israel formed in the Middle East, and Greek city-states began experimenting with new kinds of government.

Twenty-five hundred years ago, Buddhism, Jainism, and Confucianism were founded. Rome became a republic, Athens a democracy.

Two thousand years ago, Rome became an empire. Christianity was founded. There were about 200,000,000 people on the planet, roughly the population of Brazil today.

Five hundred years ago, Europeans began colonizing the Americas, and the first slaves were taken from Africa to the New World. Firearms began their dominance the battlefield. Michelangelo created David. The Protestant Reformation began, leading to greater questioning of religious authority in Europe. Modern scientific methods were developing, greatly advancing the rate of discovery and learning about the world around us.

Two hundred years ago, the Age of Steam had begun, and man began using fossil fuels to multiply his industry. Jenner learned to defeat viruses through vaccination. There were now one billion people on the Earth.

One hundred years ago, electricity was being wired throughout the world. The internal combustion engine was replacing the steam engine, and oil was pumped out of the ground to feed it. There were now nearly two billion people on the earth.

Fifty years ago, we were preparing to send humans to the moon. Television and radio dominated our communication. Antibiotics were discovered. We had finally learned about the role of DNA in life, the first time that anything life had evolved was capable of understanding what it was. There were three billion people on the Earth.

Twenty five years ago, personal computers were just catching on. We were sending probes to all of the planets in our solar system, and even sent two out of the solar system. For the first time, we had a reusable spacecraft. There were now five billion people on the planet.

Today, there are seven billion people on the Earth. We dominate the biosphere, molding it to suit our desires. We have removed tens of millions of years of ancient carbon from under the earth, and converted it back into CO2 in roughly 100 years. Like the ancient microbes three billion years ago, we are changing the atmosphere with our waste products, and have nearly doubled the CO2 level back to where it was at the time of the dinosaurs. We had even begun destroying the ozone layer which allowed life on land in the first place; luckily, scientists realized what was going on and people had the political will to at least keep it from growing larger. Our effluent is changing the ocean as well, with industrial and agricultural run-off creating larger and larger dead zones each year.

So this is the perspective I want to impart. We didn’t have to happen. Life may be common everywhere there is liquid water and carbon in the universe, but sentient life is really hard to get to. It took a lot of near perfect conditions to get to us. Our planet is just the right size, with just the right composition, around just the right star. We aren’t constantly bombarded with space debris. There are not dozens of unstable stars nearby to soak us with radiation, or strip away our planets, or bombard us with their own debris. Our catastrophic disasters have never been completely catastrophic, and our planet was able to recover from its greenhouse states and its iceball states, often with the help of the life that evolved on it.

If there had been another giant meteor in the past 50 million years, or another massive volcanic eruption, or if more of our continents had drifted back over the poles, we would probably not be here. We are very lucky or very blessed to be what we are. If anything different had happened, we still might be in the trees, flinging crap at the lions below. If there were even trees.

Furthermore, now that we are here, we don’t know how long we have until the next natural mass extinction event comes, or how bad it will be. We may have ten million years to figure out how to get off this rock and spread out a little more, or just a thousand. We don’t know if it will make the Earth go iceball for a few hundred million more years, or go greenhouse, or just simply sterilize the surface.

For those who think that “the Earth is just too big for people to change” – consider that primitive single-cell lifeforms were able to change our atmosphere entirely, turning us from a methane greenhouse to an oxygen snowball. Yeah, it took them hundreds of millions of years, but they also had nowhere near our industry. We don’t just work with the carbon around us, we dig up buried carbon that is the remains of millions of years of photosynthesis and life’s chemistry, and burn it straight back into carbon dioxide. Not just for us, but also to feed our extremely inefficient machines. We transport our food from hundreds or even thousands of miles away. As westerners, we burn fossil carbon for practically everything we do. There is a steady trickle of carbon dioxide from somewhere in the world caused by you reading this essay on your computer.

Do this simple exercise for me. Grab a CD you aren’t fond of, and a very sharp pencil. Trace around that CD onto a piece of paper, and pull the CD away. That circle represents Earth. That line represents the part of Earth that is capable of supporting life. Except, it is ten times too thick! Five miles above sea level to five miles below is as far as life goes, and 99% of life happens within 2 miles of sea level. Look at a picture of Earth from space, or looking back from the Moon. You don’t see a thick atmosphere radiating out. It is a thin, fragile thing. Life is a thin film on the surface of a giant rock, nurtured and shielded by a faint wisp of air which is in turn protected by the electromagnetic field from our core.

For the nihilists and cynics who think humanity or life can get a fresh or better start once we are gone – yeah, maybe. Or maybe we are the best it is ever going to do. We don’t know if Earth is ever going to get another 65 million years of relative calm to evolve something like us again. We do know that even if it does, whatever comes after us will not find a rich carbon energy source so readily available – we have already used it up, and 65 million years is not going to replenish it, especially if life remains very sparse after we wreck the biosphere. Whatever comes after us will never get the massive technological jump that fossil fuels gave humans, which means they may not be able to get off this rock before something else bad happens to it. All of the life on Earth is depending on us to carry it further into the universe.

For the religious zealot who thinks Jesus will come back before it’s a problem – pretty doubtful at this point. Christians have been thinking that for almost 2000 years now. If you are of European descent, you quite likely had an ancestor one thousand years ago who thought Jesus was going to be back in their lifetime. You, their grandchild fifty generations removed, are still waiting. Do you want to have great grandchildren to carry on the tradition, to maybe be alive when it finally does happen? Or are you going to arrogantly burn up this world, assuming yours must be the generation lucky or deserving enough to be Raptured away from the tortured heathens, like so many of your ancestors before you did?

It took four and a half billion years to make us. We are on a course to eliminate ourselves in a few hundred. It really is that bad. A warmer Earth grows less food. A warmer Earth shrinks the coastlines where much of our population exists. A warmer Earth has more areas where humans simply cannot live in large numbers without absurd levels of energy usage; in a hundred years at our current warming trend, there will be many places on Earth where a human or animal simply cannot go outdoors for any length of time in the day, where temperatures will be approaching 130F to 140F. It is likely that most of you reading this will see starvation and food wars in your lifetimes, and certainly within the lifetime's of today's children.

We have to change how we live. We have to be smarter and more responsible, less willfully ignorant and selfish. Otherwise, we are going to cause a dieback to rival the worst mass extinctions in the planet’s history, and possibly doom this world’s only chance to develop life capable of making its own destiny.

**Edit** Thank you so much for the Community Spotlight and all the comments! I am honored!

Originally posted to mattakar on Thu Nov 29, 2012 at 08:14 AM PST.

Also republished by Community Spotlight.


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