The universe is 13.8 thousand million years old. We are going to imagine all of the cosmic time, and in order to do that, let's compress it into a single calendar year. The cosmic calendar begins on January 1st with the birth of our universe. It contains everything that's happened since then, up to now, which on this calendar is midnight December 31st. On this scale, every month represents about a billion years. Every day represents nearly 40 million years. Let's go back as far as we can, to the very first moment of the universe. January 1st, the Big Bang. (explosion) It's as far back as we can see in time... for now. Our entire universe emerged from a point smaller than a single atom. Space itself exploded in a cosmic fire, launching the expansion of the universe and giving birth to all the energy and all the matter we know today. I know that sounds crazy, but there's strong observational evidence to support the Big Bang theory. And it includes the amount of helium in the cosmos and the glow of radio waves left over from the explosion. As it expanded, the universe cooled, and there was darkness for about 200 million years. Gravity was pulling together clumps of gas and heating them until the first stars burst into light on January 10th. On January 13th, these stars coalesced into the first small galaxies. These galaxies merged to form still larger ones, including our own Milky Way, which formed about 11 billion years ago, on March 15th of the cosmic year. Hundreds of billions of suns. Which one is ours? It's not yet born. It will rise from the ashes of other stars. See those lights flashing like paparazzi? Each one is a supernova, the blazing death of a giant star. Stars die and are born in places like this one -- a stellar nursery. They condense like raindrops from giant clouds of gas and dust. They get so hot that the nuclei of the atoms fuse together deep within them to make the oxygen we breathe, the carbon in our muscles, the calcium in our bones, the iron in our blood, all of it was cooked in the fiery hearts of long-vanished stars. You, me, everyone -- we are made of star stuff. This star stuff is recycled and enriched, again and again, through succeeding generations of stars. How much longer until the birth of our Sun? A long time. It won't begin to shine for another six billion years. Our Sun's birthday is August 31st on the Cosmic Calendar... ...four and a half billion years ago. As with the other worlds of our solar system, Earth was formed from a disk of gas and dust orbiting the newborn Sun. Repeated collisions produced a growing ball of debris. See that asteroid? No, not that one. The one over there. We exist because the gravity of that one next to it just nudged it an inch to the left. What difference could an inch make on the scale the solar system? Just wait, you'll see. The Earth took one hell of a beating in its first billion years. Fragments of orbiting debris collided and coalesced, until they snowballed to form our Moon. The Moon is a souvenir of that violent epoch. If you stood on the surface of that long ago Earth, the Moon would have looked a hundred times brighter. It was ten times closer back then, locked in a much more intimate gravitational embrace. As the Earth cooled, seas began to form. The tides were a thousand times higher then. Over the eons, tidal friction within Earth pushed the Moon away. Life began somewhere around here, September 21st, three and a half billion years ago on our little world. We still don't know how life got started. For all we know, it may have come from another part of the Milky Way. The origin of life is one of the greatest unsolved mysteries of science. That's life cooking, evolving all the biochemical recipes for its incredibly complex activities. By November 9th, life was breathing, moving, eating, responding to its environment. We owe a lot to those pioneering microbes. Oh, yeah-- one other thing. They also invented sex. December 17th was quite a day. Life in the sea really took off, it was exploding with a diversity of larger plants and animals. Tiktaalik was one of the first animals to venture onto land. It must have felt like visiting another planet. Forests, dinosaurs, birds, insects, they all evolved in the final week of December. The first flower... bloomed on December 28th. As these ancient forests grew and died and sank beneath the surface, their remains transformed into coal. 300 million years later, we humans are burning most of that coal to power and imperil our civilization. (whooshing) Remember that asteroid back in the formation of the solar system-- the one that got nudged a little to the left? Well, here it comes. It's 6:24 AM on December 30th on the Cosmic Calendar. (impact thundering) For more than a hundred million years, the dinosaurs were lords of the Earth, while our ancestors, small mammals, scurried fearfully underfoot. The asteroid changed all that. Suppose it hadn't been nudged at all. It would have missed the Earth entirely, and for all we know, the dinosaurs might still be here but we wouldn't. This is a good example of the extreme contingency, the chance nature, of existence. The universe is already more than 13 and a half billion years old. Still no sign of us. In the vast ocean of time that this calendar represents, we humans only evolved within the last hour of the last day of the cosmic year. 11:59 and 46 seconds. All of recorded history occupies only the last 14 seconds, and every person you've ever heard of lived somewhere in there. All those kings and battles, migrations and inventions, wars and loves, everything in the history books happened here, in the last seconds of the Cosmic Calendar. But if we want to explore such a brief moment of cosmic time... ...we'll have to change scale. We are newcomers to the cosmos. Our own story only begins on the last night of the cosmic year. It's 9:45 on New Year's Eve. Three and a half million years ago, our ancestors, yours and mine, left these traces. We stood up, and parted ways from them. Once we were standing on two feet, our eyes were no longer fixated on the ground. Now we were free to look up in wonder. For the longest part of human existence, say the last 40,000 generations, we were wanderers, living in small bands of hunters and gatherers, making tools, controlling fire, naming things, all within the last hour of the Cosmic Calendar. To find out what happens next, we'll have to change scale to see the last minute of the last night of the cosmic year. We're so very young on the time scale of the universe that we didn't start painting our first pictures until the last 60 seconds of the cosmic year, a mere 30,000 years ago. This is when we invented astronomy. In fact, we're all descended from astronomers. Our survival depended on knowing how to read the stars in order to predict the coming of the winter and the migration of the wild herds. And then, around 10,000 years ago, there began a revolution in the way we lived. Our ancestors learned how to shape their environment, taming wild plants and animals, cultivating land and settling down. This changed everything. For the first time in our history, we had more stuff than we could carry. We needed a way to keep track of it. At 14 seconds to midnight, or about 6,000 years ago, we invented writing. And it wasn't long before we started recording more than bushels of grain. Writing allowed us to save our thoughts and send them much further in space and time. Tiny markings on a clay tablet became a means for us to vanquish mortality. It shook the world. Moses was born seven seconds ago. Buddha, six seconds ago. Jesus, five seconds ago. Mohammed, three seconds ago. It was not even two seconds ago that, for better or worse, the two halves of the Earth discovered each other. And it was only in the very last second of the Cosmic Calendar that we began to use science to reveal nature's secrets and her laws. The scientific method is so powerful that in a mere four centuries, it has taken us from Galileo's first look through a telescope at another world to leaving our footprints on the Moon. It allowed us to look out across space and time to discover where and when we are in the cosmos. CARL SAGAN: We are a way for the cosmos to know itself.
References: Cosmos A Space Time Odyssey, Standing Up in the Milky Way
