What happened 4715 years ago? In Chinese myth and religion, apparently 2698 BC (on the Gregorian calendar) was the beginning of the reign of the Yellow Emperor, thought to be the "initiator of Chinese civilization" according to Wikipedia. That's not to say that the Chinese didn't exist before then, but his place at the beginning of their calendar at least signifies an important distinction between what came before and everything after. Of course, there are a LOT of historical reasons for the way the current Chinese calendar is formulated.
Placing Year One on a calendar at the beginning of civilization makes a lot of sense. Calendars are an invention of civilization. They don't just tell time, they tell a story about the culture it belongs to. For example, the current year on the Hebrew calendar is 5777, with Year One taking place a year before the creation of the world in the Jewish myth of Genesis.
The calendar used all over the world today, the Gregorian Calendar, is of course a Christian invention, placing Year One at the birth of Jesus of Nazareth. This calendar frames the history of Western civilization, and indeed the entire world, as the story of a Christian world. But Western civilization, and indeed civilization as a whole, is far older than that. Why should the world run on a calendar based around a religion followed only by a third of the people in it?
I think there's something very satisfying about placing Year One at the beginning of civilization, as it marks the beginning of humanity as we know it today. The distinction is important, as humanity was thought to have achieved "behavioral modernity" about 50,000 years ago, which means that the project of civilization itself is a a relatively new one in the history of our species. We are still sorting through the various ways the environment of civilization has forced us to evolve, be it physically, mentally, socially, or otherwise.
But when to put Year One on the calendar of civilization? Western civilization is thought to have its roots in ancient Mesopotamia (meaning "between rivers": the Tigris and Euphrates, located in current-day Iraq and Syria). The first civilization to be founded there is thought to be Sumer, from which we get the story of Gilgamesh.
There's no exact date on the founding of Sumerian civilization, as written records from that time didn't emerge until a good while after the Sumerians arrived on the scene. Additionally, there is some debate among historians about when to place such a date, with some saying around 4000 BC and some saying a good deal older. However, that ~4000 BC date seems to be what is conventionally accepted, as it is the beginning of the Uruk period, named after the city of Uruk, thought to be the oldest of the Sumerian cities. Additionally, the fourth millennium BC is the beginning of the Bronze age, marking a significant departure in human development.
So, if one wanted to create a calendar based on the story of civilization (or at least Western civilization, as the Chinese and Indians popped up separately, and around the same time as the Mesopotamians), one might simply add 4000 to our current year, which would make this year 6017. That's 6,017 years of organized agriculture, social stratification, government, written history, taxes, population density, specialist occupations, and politics, things we all take for granted today. That's 6,017 years out of 50,000 years of behavioral modernity, a mere 12% of the existence of humanity.
I think this is a fascinating, and even useful, formulation of time. In today's world we are still dealing with the problems posed by civilization, be it social stratification, the concentration of power, the effect on the environment, and the roles that it forces us into in order to survive. And there's a rich history in those 4000 unacknowledged years, from which the basis of our culture today was formed. I think we are better off looking at the bigger picture.
Here are some important historical dates revised with 4000BC as Year One (subtract all BC years from 4001). I separated them by millennia. I know this is lacking quite a lot, and it's very U.S.-centric, but I'm not trying to give a history of the whole world here. Significant dates in the history of the Roman Empire are in bold because of the significant through-line it makes in Western history.
- 1: Sumerian Civilization in Mesopotamia
- 801: Invention of writing in Egypt and Mesopotamia
- 851: Unification of Egypt and founding of First Dynasty
- 1111: Second Dynasty of Egypt
- 1300: Minoan Greek Bronze Age
- 1200~1500: Estimated date that Gilgamesh ruled Uruk
- 1461: Great Pyramid of Giza built during Fourth Dynasty of Egypt
- 1503: Fifth Dynasty of Egypt
- 1651: Akkad arises from Sumeria
- 1871: Tenth Dynasty of Egypt
- 1900: Sumerian poems of Gilgamesh dated to around this time
- 1951: Assyria gains independence from Sumeria
- 2000: Canaanite city-states founded in the levant
- 2107: Babylon arises from Akkad
- 2401: Mycenaean Greece
- 2561: Moses leads the Jewish people out of Egypt (estimated date)
- 2689 - 2729: Writing of the Torah
- 2722: Ramesses II rules Egypt as part of Nineteenth Dynasty
- 2807~2817: Estimated date of Trojan war
- 2824: Bronze Age Collapse, affecting Egypt, Greece, and much of the Mediterranean. The Greeks lose the ability to write.
- 2976: King Saul rules the Kingdom of Israel and Judah, followed by David and Solomon (estimated)
- 3041: Solomon's temple in Jerusalem completed
- 3200s: Greeks adopt alphabet from Phoenicians
- 3240-3290s: The Iliad is written, followed soon by the Odyssey
- 3248: Founding of Roman Kingdom
- 3261: Assyria conquers Israel
- 3396: Jewish Babylonian captivity
- 3407: Athenian Greek Democracy
- 3415: Destruction of Solomon's Temple by Babylon Empire
- 3434: Birth of Buddha
- 3451: Zoroaster, founding of Achaemenid empire
- 3462: Fall of Babylon to Achaemenid Empire, Cyrus the Great releases the captive Jews the next year
- 3476: Fall of Egypt to Achaemenid Empire
- 3485: Second Temple in Jerusalem constructed
- 3492: Founding of Roman Republic
- 3511: Battle of Marathon, between Greece and Achaemenid Empire
- 3521: Battle of Thermopylae, second invasion of Greece by Achaemenid empire
- 3561: Herodotus' Histories published
- 3669: Alexander the Great conquers Egypt, then Judea, the next year conquers Achaemenid Empire
- 3721 - 3871: Septuagint (Greek translation of Hebrew Bible) written
- 3855: Roman rule of Greece
- 3956: Julian Calendar adopted (709 AUC - 709 years since founding of Rome)
- 3957: Death of Julius Caesar
- 3971: Ptolemaic Egypt falls to Rome
- 3972-3982: Virgil writes the Aeneid
- 3974: Founding of Roman Empire
- 3997: Jesus of Nazareth is born
- 4030: Jesus executed by Rome for the crime of sedition
- 4070: Rome besieges Jerusalem and destroys the Second Temple. Books of the New Testament written in Greek.
- 4284: Emperor Diocletian splits Rome in two, with the eastern capital in Byzantium, later called Constantinople
- 4325: First Council of Nicaea, organized by Emperor Constantine
- 4391: Library of Alexandria in Egypt destroyed by imperial decree against paganism
- 4476: Fall of Western Rome during age of Germanic migration
- 4632: Death of Mohammed
- 4639: Egypt, ruled by Eastern Rome, falls to Islamic Empire
- 4793: Viking age
- 4800: Charlemagne, Holy Roman Empire
- 5066: William the Conqueror invades and rules England
- 5095 - 5192: First - Third Crusades
- 5202 - 5204: Fourth Crusade, including sacking of Constantinople
- 5215: Signing of the Magna Carta
- 5337 - 5453: Hundred Years' War between England and France
- 5346 - 5353: The Black Death
- 5453: Fall of Byzantine Empire (Eastern Rome) to Ottoman Empire
- 5475: The Printing Press
- 5492: Columbus discovers America
- 5517: Protestant Reformation
- 5582: Gregorian Calendar adopted
- 5650: Age of Enlightenment/Scientific Revolution
- 5754-5763: Seven Years' War
- 5760: Industrial Revolution
- 5776: Declaration of Independence (United States)
- 5789-5799: French Revolution
- 5804: Napolean titled Emperor of France
- 5806: Fall of Holy Roman Empire to Napolean
- 5821: Greece gains independence from Ottoman Empire
- 5861: U.S. Civil War and end of slavery
- 5870-5871: Franco-Prussian War, resulting in formation of French Republic and German Empire
- 5914: World War I
- 5920: Women granted right to vote (U.S.)
- 5939: World War II
- 5963: Civil Rights (U.S.)
- 5990: Widespread use of the Internet
- 6001: 9/11
- 6017: Today
EDIT: A friend just sent me the following video, proposing a different scheme for setting the era.
I personally prefer starting the calendar at the beginning of Sumerian civilization for my reason stated above, that the calendar itself is an invention of civilization, and civilization itself was a major turning point for humanity in that it permanently altered our environment. As the Indus Valley civilization and Chinese civilizations were getting started around the same time, it would be just as inclusive. Instead of HE: the Human Era, I'd propose HC: Human Civilization. All prehistoric achievements like the first temples would be marked as BHC.