Below are the top ten turning points, i.e. the "Top Ten Stories of All Time". Of course there are stages within these stages, and additional stages could be added--there could easily be 20 - 30 key stories/stages--but this list is an attempt to keep it short. Note that the exact dates given below are still being debated. The key is the turning point itself, not the precise date.
(Imagine Sensational Headlines from the Cosmic Chronicle or the Galactic Gazette or, later, the Daily Planet)
1. STARTING WITH A BANG, or WHAT'S THE MATTER? (13.7 billion years ago)
As described by Michio Kaku in his first five stages, the universe emerged from a point smaller than an atom--the Big Bang-- and has been expanding ever since. For 380,000 years after the Big Bang radiation was so intense that atoms could not form. When the universe cooled enough for electrons and protons to stick, it came to a dramatic turning point--radiation passed into the background and the universe burst into light. For the new stage of matter to begin, the electromagnetic attraction of electrons to protons had to become stronger than the radiation left over from the Big Bang that kept knocking them apart. Today, thanks to the WMAP satellite, we have photos of the baby universe just after it became visible. Click here for a photo of the newborn universe
2. A STAR IS BORN--(ongoing, starting 200-300 million years after the Big Bang)
The early universe was almost uniform in all directions but there was just enough unevenness that gravity could pull matter into galaxy sized clouds and even tighter clumps. When enough matter squeezes together, it reaches a turning point--atoms of hydrogen start to fuse into helium, creating a twinkling hydrogen bomb, i.e. a star. A star maintains a balance between the gravitational energy of the star pressing in with the outward pressure from the nuclear fusion reaction.
3. SUPERNOVA - THE UNIVERSE STRIKES GOLD (various times, one in our region of the galaxy perhaps 5 billion years ago)
When a very large star runs out of fusible atoms, it collapses all at once. Consider how much energy is released if you drop a brick on your foot, or if a building collapses. Now try to imagine a whole star, ten times bigger than the sun, all collapsing in a few seconds! This is a supernova. The collapse comes to a sudden halt when the center of the star becomes solidly filled by neutrons. At that point the onrushing collapsing matter of the star rebounds from the neutron core and collides with the additional matter still rushing in. The explosion is so powerful that atoms heavier than iron--e.g. gold, silver, lead--are fused into being. These heavy atoms are flung into the region of space surrounding the supernova. Click here for more information about supernovas, including an explanation of how supernovas act as standard candles to measure the distance to far away galaxies.
4. BIRTH OF MOTHER EARTH (4.5 billion years ago)
In the aftermath of a supernova, gravity gradually pulled matter (including lots of hydrogen and helium left over from the Big Bang) together to form a new generation star--the sun. This time, the star was surrounded by clumps of heavier elements, created in the supernova. Gravity pulled these elements together to form planets. A planet is a balance of gravity pulling in and electromagnetic forces (the electrons in the outer shells of atoms) pressing back. The gravity in a planet is not strong enough to tear the atoms apart, which is good for us; otherwise the earth would be a star.
The most dramatic moment in the birth of the earth came with the collision of the two largest clumps--the early earth and a clump about 1/10 that size. This was dubbed The Big Splat in a book with that title by Dana MacKenzie, (John Wiley & Sons, Hoboken, NJ, 2003). The big splat was 4.5 billion years ago; it led to the formation of the moon over the next 50 million years.
Although oceans formed about 100 million years after that, a deluge of meteorites about 3.9 billion years ago made earth pretty inhospitable for the next 100 million years. Which brings us to . . .
5. IT'S ALIVE! (about 3.8 billion years ago)
After the big splat and the big meteor shower, self replicating DNA appeared in the form of single cells that used chemicals in their environment to reproduce--the Archeans. Just how the early life forms emerged is still a matter of debate (volcanic vents under the ocean are looking like a likely birthplace), but the leap from non-replicating matter to replicating matter is certainly a qualitative change.
6. SEX CELLS (very roughly one billion years ago)
From the beginning of life for nearly 3 billion years, single cells, also called prokaryotes, evolved slowly by mutation. One major mutation was the appearance of cells that learned to use the sun's energy to reproduce (photosynthesis) about 2.6 billion years ago. These were cyanobacteria.
The next important mutation was about 1.8 billion years ago. Apparently, an Archaen swallowed a cyanobacteria, or the other way around, and made the first eukaryote-- a cell with a nucleus. These were well designed to take advantage of oxygen in the atmosphere. Good timing too, since the cyanobacteria had been busy polluting the atmosphere with this gas, which was poisonous to most of the earlier prokaryotes.
The eukaryotic algae thrived on oxygen, but still evolved slowly as single celled organisms. Gradually they lumped together into multi-cellular slime molds and such life forms. The big breakthrough came about one billion years ago when cells learned to reproduce by mixing their DNA with a partner's. This meant that offspring were no longer carbon copies (so to speak) of their parents, but could exhibit altogether new traits. These natural variations gave rise to rapid evolution of many new life forms.
It took about 400 million more years for fossils to start showing up as remnants of more solid life forms. At that time, 543 million years ago, the Cambrian explosion reveals a myriad of living creatures. In his book, In the Blink of an Eye, Andrew Parker makes an excellent case that the origin of the eye, in trilobytes, caused all other life forms to develop hard shells or get eaten. Therefore the sudden appearance of many fossils was a consequence of the evolution of sight. Animals evolved many other useful survival mechanisms such as spinal columns, ears, noses, taste buds, hands, and feet, all of which we are grateful for now.
While the exact process of the turning point to sexual reproduction is not fully understood (at least not by me), the transition from pre-sex to sex is qualitative (just ask any teenager who has just discovered sex!)
7. DINOSAURS DIE/MAMMAL MANIA (65 million years ago)
Following the sexual revolution of a billion years ago plants and animals evolved rapidly. Along the road, however, there have been several mass extinctions. The biggest one was 250 million years ago, when 95% of all species perished. The most important recent one for human history was caused by an asteroid that crashed into the Gulf of Mexico about 65 million years ago. This led to the demise of the dinosaurs and the rise of the mammals. The opposing forces in this case could be seen as the momentum of the asteroid colliding with the earth. The opposing forces could also be seen as the resulting blanket of dust that brought about freezing conditions all over the earth, and the inability of many species to survive the deep freeze. Somehow the mammals--warm blooded, breast feeding creatures who previously had to scurry to avoid the grasp of the mighty dinosaurs--survived and suddenly had virtually no predators to fear. Over the next few million years they evolved into predators themselves (lions and tigers and bears--Oh, my!) as well as prey (antelope, rabbits, mice, etc.) They also filled many niches such as oceans (whales, dolphins, seals), and trees (monkeys). Those clever little monkeys developed stereoscopic eyes to judge distance--very handy for jumping from branch to branch, and later very useful for judging when it is safe to cross a busy street. They also developed opposable thumbs, handy for hanging onto branches, and, later, for typing articles about cosmology and evolution. Click here for a graphic of geologic time from the US Geological Survey
8. HERE COME THE HOMININS (10 million years to 60,000 years ago)
It is still a big leap from the tree tops to the tribe, and it includes a few intermediate steps. The apes put us on the path to being human with their relatively large size and increasing brain size 10 million years ago. But the hominins mark the real leap from the animal world to human society starting about 3 million years ago (terminology keeps changing, but in 2008 the term hominin refers to a subgroup of the hominids, which include the chimpanzees and gorillas.) At least six types of hominins (counting us) developed sharp spears to hunt animals, learned to control fire, built loyal tribal societies, learned to speak, and spread around the globe from their African origins. For today's humans, the final qualitative leap to our present human race came with a migration of homo sapiens from Africa only about 60,000 years ago. Our ancestors supplanted (killed?) the Neanderthals and any other hominins who had preceded them if they were still around. Since 60,000 years is merely an eyeblink in evolutionary history, it is clear that all humans today are practically brothers and sisters.
Click here for an illustration from the American Museum of Natural History showing human migration from Africa
9. CIVILIZATION HO! (8,000 years ago to present)
The invention of agriculture about 8,000 years ago marked the next big transition--from hunting and gathering to farming as a way of life. Agriculture meant that people could stay put, and that surpluses existed for some people to engage in other work--priests, soldiers, merchants, prostitutes, emperors, etc. Keeping track of all that grain led to writing and the beginning of recorded history.
10. HOW YOU GONNA KEEP 'EM DOWN ON THE FARM? (200 years ago to present)
Incredibly, we are living in the midst of the latest turning point. Beginning a mere 200 years ago, the industrial revolution has transformed society from rural to urban. And the pace of the revolution is accelerating. Important inventions such as the steam engine, railroad, and telegraph have given way to automobiles, televisions, cell phones, and computers. In 1800 less than 4% of the people lived in cities with a population over 5,000. A hundred years later that figure had risen to 10%. Now half live in urban areas. The UN estimates that 2/3 of all people will live in urban areas by 2050. Even those who don't live in cities are increasingly being brought into a global society through television and communications technologies. The world's population has exploded from 1 billion in 1804, to 2 billion in 1927, to 6 billion today. Whether this population and this high-tech lifestyle is sustainable remains to be seen. Click here for a UN graph of world population (see page 7)
So our universe has had an exciting ride from the Big Bang to the baby boom. It's not a difficult story to understand--especially with the tool of dialectics to spot all the turning points--and it's a story that everyone deserves to know. Of course there are still lots of unanswered questions--what came before the big bang?, what is dark matter?, what is dark energy?, how did life/DNA originate?, etc.--so there is no shortage of exciting scientific puzzles to be solved.
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