字幕表 動画を再生する 英語字幕をプリント As far as we know, around 4,500 million years ago this rock that we live on coalesced from the dust and debris left over from the formation of our sun. Without airplanes, pizza delivery, or the Internet, things moved more slowly across the early earth than they do today. For example, from isolated puddles of water, the oceans formed over the course of 400 to 800 million years. That's how long it would take for your hair to grow around the earth - twice. In that same time, bacterial life did spread across the watery globe. Higher plants and animals, on the other hand, took much longer to develop and disperse. But we're going to skip those 3 billion years (during which your hair would have grown to the moon) and talk about us, Homo sapiens. We were much faster than our own hair, which would have grown a meager 27km in the 180,000 years we took to cross Africa and reach all the unfrozen continents. In many of these places we were able to develop useful practices like agriculture, but because we were scattered across the globe, the best ideas and tastiest regional foods could only gain ground through trade or human migration. Wheat, for example, was domesticated around 8500BC to make porridge. Actually, some speculate it might have been for beer, but either way wheat made it from the Fertile Crescent to both the Atlantic and the Pacific by roughly 2500BC. 6000km in 6000 years might seem like a blistering pace, but just wait for the Middle Ages! The bubonic plague and the printing press each spread across Europe in less than a hundred years, bringing death and literacy to the populace before their hair could have even grown 15 meters. In the 20th century, mania for both the Beatles and the Hula hoop raced around the world in a year or two. Now even a year is a long time. With millions of people jetsetting across the globe every day, diseases such as SARS can vacation almost anywhere within a few short weeks. And the 0s and 1s that make up this video take, on average, less than a tenth of a second to get to you - that's about half a nanometer, or two atoms, of hair growth. In short - the pace of travel on earth has really sped up! But how do we know this stuff? How do we know what happened on earth before the records of written history? Why do we think the earth is 4,500,000,000 years old? And what on earth is going to happen in the next 45 years? Welcome to the story of what we know about the earth and how we know that we know it. This is MinuteEarth.