Having posted my “sermon” on the size of the universe (over 200 billion galaxies/over 100 billion stars per galaxy. Do the arithmetic.), I could not help asking questions about our home planet. How did life begin here and why? How has it evolved? What Big Picture stuff can we take away? It is amazing how much we have learned just over the past several decades and how the mysteries of the Planet Earth are just as awesome as the mysteries of the universe. I have spent the last week rereading Sapiens by Yuval Noah Harari (a terrific book) and surfing the web about life on prehistoric Earth. Here is what I have learned:

It took a long time for life to get started on our blue planet.

Our solar system was formed 4.6 billion years ago about nine billion years after the Big Bang. A star was formed, our Sun, from the cloud of collapsing dust and gas, in an unremarkable corner of the Milky Way galaxy. The material left over after the Sun’s formation coalesced to form planets and everything else in our solar system. It is not certain exactly what happened after the Earth, which in its early years can best be described as a molten, round mass, began to cool and become a solid form. Many scientists now believe a Mars-sized planet (named “Theia”) struck young Earth. Molten debris, streamed out from the collision, and produced the moon. All this activity happened in our solar system’s first half billion years. We also don’t know exactly when life began on Earth. It is possible life came into existence and was wiped out multiple times by giant impacts before taking hold for good. Our earliest direct evidence of life dates to about 3.5 billion years ago, about a billion years after the solar system formed—the arrival of single cell creatures.

For life to form you need four key elements—hydrogen, oxygen, carbon, and nitrogen. You also need water, so hydrogen and oxygen must have combined toward the end of this pre life period. And about 2.7 billion years ago a microscopic organism named “cyanobacteria” (Also known as blue-green algae) emerged and began using sunlight, carbon dioxide, and water to produce food through photosynthesis. The byproduct of photosynthesis is oxygen.

At first, the oxygen produced by cyanobacteria was sequestered in minerals and seawater. But around 2.5 billion years ago, bacteria were producing enough oxygen to be stored in Earth’s atmosphere.

Meanwhile, microbes began innovating and evolving. Some grouped together, forming the precursors of more complex life. Simple, oxygen-based life began to emerge, such as sponges, but it took a very long time for this to happen—another two billion years.

During this period, land, caused by underwater volcanoes, began to form, rising above the surface of the ocean. Then after a very long period of over another billion years, around 500 million years ago the first sea animals appeared; and  450 million years ago,  fish-like vertebrates crawled their way out of the sea onto the land. Continents came and went over the millennia eventually producing a giant continent called “Pangea,” around 250 million years ago. The Pangea land mass included most of the land on the planet and prevailed for about 25 million years before it started to break apart, forming the continents and oceans we have today.

By this time Earth’s oxygen levels had hit 20%, which is roughly the percentage they are today. Plant life, which produced much more oxygen, also flourished. The stage was set for some legendary animals to appear, like dinosaurs and (eventually) us humans. Dinosaurs evolved and roamed the Earth starting 250 million years ago — an extraordinary run that lasted  almost 200 million years, ending 66 million years ago when a  6.2-mile-wide object struck the planet causing the largest of five mass extinctions of animals and plant life that occurred over several hundred million years. Experts think climate change was the main culprit of most mass extinctions.

We humans—Homo sapiens— are late arrivals.

 The first human-like ancestors appeared between five million and seven million years ago, probably when some apelike creatures in Africa began to walk habitually on two legs. The last common ancestor shared between humans and great apes and chimpanzees lived between seven and 13 million years ago. In 1974 “Lucy,” a skeleton dating back 3.5 million years, was discovered in what is now Ethiopia. These early human-like creatures probably looked more like chimps than they look like us. It was not until 300,000 years ago that Homo habilis, the first “modern” human, evolved, giving birth to the genus Homo. Think about that for a moment. Only 300,000 years ago? My goodness, that is like yesterday in the context of a planet which had been in existence for over 4.5 billion years. Why did it take so long?

Plus, there were several other early “modern” humans. We Homo sapiens were not the first but rather the last to evolve. There used to be agreement among scientists that there were eight species of “modern” humans, but some scientists now believe there were probably dozens, perhaps more. The most prominent besides us Homo sapiens were Homo erectus, who roamed the Earth for 1.8 million years beginning around two million years ago, and Homo Neanderthal, who predated us by about 100,000 years and lasted until about 28,000 years ago for a span of more than 300,000 years, overlapping with us for about half of that time. We sapiens began our journey around 200,000 years ago, probably evolving from Homo erectus. And here we are, still going strong. All the other species have folded, several hanging on as late as 30,000-40,000 years ago.

It is a tough world.

We know so much more now than we did only decades ago. This is what stands out to me:

Life on the planet has never been stable and never will be. The climate change deniers are right when they note that the climate has always been in flux, bouncing around from hot to cold, often with disastrous results for animal and plant life. Oceans have risen and fallen. Ice ages have come and gone. Earthquakes and volcanoes have disturbed the landscape and destroyed habitats. There have been at least five mass extinctions, wiping out millions of species of plants and animals, mostly due to climate change.

 The big difference today is that climate change is happening much faster due mainly to the carbon we Homo        sapiens began releasing into the atmosphere beginning with the Industrial Revolution. This time we are the responsible ones.

We Homo sapiens—the last modern humans standing—may think we are a predetermined product of a progressive evolutionary  process, but it is more complicated than that. That we survived and our cousins, the Neanderthals, didn’t may be due to blind luck. Some would insist it was Divine will. In any event a key to the “success” of all us humans has been attributed to the size of our brain compared to our size. This allowed the early humans some 2.5 million years ago to begin to outfox the competition and slowly move up the food chain.

Note, however, that the human brain today is just a tad larger than that of the first Homo sapiens who evolved about 200,000 years ago. Hey, these cavemen and cavewomen were just as smart as we are! And given their times, they accomplished just as much if not more. Afterall, early humans learned how to tame fire, to make stone tools and weapons without using blueprints,  to band together as families and tribes, to make crude habitats, and even to make enduring art. They invented spoken language and were the first species to imagine things they could not feel, touch, or see. And they survived and flourished in a hostile living environment. Some humans today are challenged by a weekend with their kids at a Boy Scouts’ camp.

What really made an impression on me was this: If you take away the long period of Homo erectus, the guys who were responsible for so many things including hightailing it out of East Africa to Eurasia, India and China and who were around for 1.8 million years, most other human species were around for periods ranging from 200,000 to 400,000 years before they disappeared from the face of the Earth. I note that we Homo sapiens now have been around for about 200,000 years. Maybe our time is up! We certainly have the weapons to wipe everything out, and who knows where climate change will take us?

Our planet, of course, will go on without us Homo sapiens. However, for the historians some hundred thousand (or hundred million) years in the future, we surely will be footnoted as just a tiny blip on the screen.

And if this history could happen on the planet Earth, what about life on other planets which happen to be in the same Goldilocks zone (not too hot and not too cold) from their star, and their planet is rocky with heat below the surface?

I also note that our solar system is now middle-aged. It has about another 4.5 billion years left before the Sun gives out. But our planet’s life in the solar system is more limited because in about one billion years, the Sun will begin its metamorphosis into a Red Giant and then a White Dwarf. As it expands outward encompassing Mercury and eventually Venus, it will make the Earth uninhabitable. We have “only” around a billion years left. The Earth is not middle-aged but old-aged. About 75% of the life of the Planet Earth may have already passed.

There are more questions than answers.

 Some may be asking why I am interested in all this in the first place. And it is not only because when I was eight, my 12 year-old neighbor reported witnessing a flying saucer land in his backyard and saw green creatures hopping out to explore our neighborhood. That got me started thinking about the universe and our place in it. Other than scientists and historians, however, why should anyone be interested in history which happened so long ago and is beyond human comprehension? We will be long gone when the end comes. Plus, it is surely the case that finding answers to the meaning of all this is beyond our pay grade. Our brains may be big for our size but not that big, and we certainly aren’t God.

 And that raises other questions: Where does God fit into this story? We Christians say “we believe God created heaven and Earth.” Does that mean “They” (I am deliberately using non binary language here. I have always had trouble understanding how God could be  a “he.”) started the Big Bang? Did They step aside once it all got going or are They still involved? Is this really the best They could do? Where might heaven be anyway? And what has been the experience of us humans on the Planet Earth as we  try to connect with the Divine?  This will be the subject of my next blog post.

Stay tuned.

YEARS
AGO
BILLIONS	Event
13.8	Big Bang
4.5	Our Solar system begins
4	First atom as gas cools
3.8	First replicating molecule (DNA ancestor)
3.5	First multi cell life (bacteria…oxygen)
1.5	continets start to form / then break up
MILLIONS
555	Multi-cellular marine life
500	Fish-like vertebrates
450	Arthropods–scorpions, spiders and mites
420	Land plants begin
360	Four-limbed vertebrets/Large forests,vast  reefs,  one ocean
250	Super continent Pangea forms, reptiles
248	First mass extinction 90% of animals perish,70% plants
225	Pangea starts to break apart/the age of dinosaurs
130	Continets drift to present positions, Dinosaurs rule the planet
65	Asteroid hits Yuccatan, Dinosaurs wiped out, mammals benefit
10	Apes appear
6	last common ancestor of apes, chimps and humans
3.2	“Lucy”
2.3	Homo habilis
2	Homo erectus
THOUSANDS
200,000	Homo sapiens