字幕表 動画を再生する 英語字幕をプリント On these African plains some 60,000 years ago our ancestors began migrating north. A trek that would ultimately give rise to modern day civilization. And it's nothing short of a miracle that we've progressed as far as we have, especially in such a short amount of time. It's really not that difficult to see why intelligent life may be extremely sparse across the universe given how absurdly fortunate we've been. So many things could've gone wrong along the way and so many times it almost did. On the morning of the 12th of August, 1883, Mexican astronomer, José Bonilla, was observing the Sun when numerous UFOs began to sweep across the solar disk. The objects were surrounded by a coronal haze and left behind a trailing mist. The phenomenon continued for two consecutive days and Bonilla counted 447 objects in total. As the event could not be explained the UFOs were simply dismissed as birds, insects, or dust passing in front of the telescope. But based upon Bonilla's description of the event coupled with an improved understanding of various astronomical phenomena, an article published in 2011 hypothesized that the objects where fragments of a comet nearly colliding with the Earth. The only bodies in the solar system that leave trails and are surrounded by a bright haze are comets. And much like this comet observed in 2006, we now know that fragmentation is a frequent occurrence. It is estimated that the comet broke into more than 3,200 fragments ranging in size between 50-1000 meters in diameter and sailed past the earth at a distance of no more than a few thousand kilometers. Had only one of these fragments struck the planet, it could have resulted in millions of casualties. Had all or at least a significant portion of the fragments impacted the Earth, we're looking at an extinction level event. It's the middle of the Siberian taiga, around 7:00 AM, when a powerful explosion would lit up the sky. An eyewitness 65 kilometers away from the blast accounts that: "...the sky split in two and fire appeared high and wide over the forest. At that moment I became so hot that I couldn't bear it, as if my shirt was on fire... I wanted to tear off my shirt and throw it down but then the sky shut closed. A strong thump sounded and I was thrown a few meters." Two decades later in 1927, the first expedition to the blast site would capture this footage. Some 2000 km² of forest, some 80 million trees in total, had been completely fattened by the event. The broad consensus is that an asteroid or comet, less than 200 meters wide, exploded a few kilometers above ground and produced a fireball as demonstrated in this simulation. Transposed over New York City its destructive power becomes a lot more apparent. [Edward Lu] This one is a little bit harder to say. The one that.. Over Tunguska, the one that was slightly larger. Had that happened over a city. Let's say New York City, we would have 7 million casualties. At least, whatever the population of New York City is, they would be gone. [Bill Nelson] Really? While the two bombs dropped on Japan marked a dramatic end to the war, they also marked the beginning of an entirely new kind of fear. A fear of annihilation by incompetence. Humans are fallible. We make mistakes. And knowing this, coupled with the realization that one mistake could result in apocalyptic levels of destruction, the likes of which had so far been reserved by nature, this new kind of fear was undeniably justified. In early October of 1960 a new early warning system on Greenland had just become operational. In the event that the Soviet Union should launch an attack against the United States, a level 5 warning would be sent to the command center located in Colorado. On October the 5th, the number on the display suddenly changed from 0 to 1. Indicating that a low-risk unidentified object had been detected. A bit strange but no immediate cause for alarm. But then the number continued to climb until a level 5 warning was issued, meaning that long-range missiles would strike the United States in less than 20 minutes. The alert quickly worked its way up the chain of command and a slight panic ensued. But it was quickly eased by the realization that Nikita Khrushchev, leader of the Soviet Union at the time, was currently visiting the United States. Not exactly where you'd expect him to be in the event of a nuclear attack. 20 minutes passed and the value of bottle caps remained the same. A subsequent investigation revealed that the base on Greenland had mistaken the rising Moon for an incoming Soviet attack. In the early morning of January the 24th, 1961, an American B-52 bomber carrying two hydrogen bombs crashed into an empty field in the state of North Carolina. Officials quickly issued a report stating that there was no cause for alarm and that there was no danger of a nuclear explosion or radiation. However, declassified documents released in 2013, reveal that one of the two bombs actually came extremely close to a full scale detonation. Three out of four safety switches erroneously activated upon impact with the ground and the slight separation of two wires was the only thing standing in the way of a nuclear explosion. Had this 3.8 Mt bomb detonated, and had the wind condition been just right, the radioactive fallout could've reached Washington, Philadelphia, and even New York. In the early 1960s, tensions between the US and the Soviet Union is strained to the breaking point and culminated in a situation known as the Cuban Missile Crisis. It is perhaps the closest we've ever come to committing omnicide. The short version is that the US installed nuclear missiles near the Soviet union, specifically in Turkey, so in response, the Soviet Union installed nuclear missiles near the United States, specifically in Cuba. The US would have none of that. "Hey, you can't do that! Only we are allowed to do that!" said the United States. "I don't know what you're talking about?" the Soviet Union replied. I'm paraphrasing of course as these where classified communications. While the impasse in and of itself came extremely close to disaster, one specific event stands out. After the US imposed a blockade to prevent the Soviet Union from exporting even more missiles to Cuba, a Soviet submarine was detected near Cuban shores. In an attempt to force the submarine to surface so that they could have a friendly chat, multiple US naval destroyers dropped low intensity explosives to signal the submarine to surface. However, the captain of the submarine misinterpreted this as an attack and ordered his men to retaliate against one of the US destroyers by launching a nuclear-armed torpedo. Fortunately, one of the two senior officers aboard disagreed with the captain's decision and eventually managed to convince him that they should surface and await orders form Moscow. And that's exactly what they did and thus the apocalypse had to reschedule. On May the 23rd, 1967, all of the early warning systems across the United States ceased to function. In fact, all manner of military communications and radar technology malfunction simultaneously and it was interpreted as intentional jamming by the Soviets. Bomber planes immediately scrambled and prepared to launch an attack. But as luck would have it just a few years prior, a branch of the US military had begun observing solar activity and its effects on the Earth. And on this day in 1967, the Sun had ejected a powerful solar storm that had stuck the planet and knocked out military defenses and other equipment. Had a project for something as unrelated as studying the Sun been delayed for just a few years, no one could've explained this nationwide interference in time to prevent World War III. In the mid 1980s squadrons of US aircrafts would often fly straight towards Soviet airspace, thus triggering their early warning systems, only to turn around at the very last moment. A form of psychological warfare that kept the Soviets on edge for an attack. In the early hours of September the 26th, 1983, the command center just outside Moscow was awoken by the sound of an alarm. An intercontinental ballistic missile had just been launched by the US and was now heading towards the Soviet Union. In the event of a nuclear attack by the Americans it was standard procedure to launch an immediate counter-attack. It was now up to the man in charge, Stanislav Petrov, to contact his superiors and to inform them that a nuclear attack was imminent. A few minutes passed when four additional missiles were detected. However, Petrov decided to go against his training and did nothing. He reasoned that if the United States were to strike, the attack would likely involve hundreds of missiles, not just a few. In other words, he suspected that this was a false-alarm. But as he had no way of confirming his suspicions, he could only wait and hope for the best. Fortunately, Petrov was correct in his assumption as evident by the fact that you are currently breathing and a subsequent investigation revealed that sunlight, reflecting of off high altitude clouds, was responsible for the anomaly. On March the 31st, 1989, two American astronomers discovered that a week prior, on March the 22nd, a 300 meters wide asteroid had come fairly close to the Earth. It had not come close enough to pose any risk of impact and was even further away than the Moon but it's still worth a mention as it passed through the exact position that the Earth had occupied a mere six hours prior. Which is in and of itself extraordinarily close on the comic scale. An impact with an asteroid of this size would obliterate almost everything within a radius of 60-75 kilometers. Superimposed over Tokyo, one of the largest cities on Earth, it looks like it would've been a rough day. Some of you may remember that a few years ago there was a lot of eschatological prophecies that the world would end in 2012. While the world is still spinning, as evident by the rotation of this globe, we did narrowly escape a catastrophic event in July of 2012. On the 23rd of July the Sun expelled something known as a coronal mass ejection or CME for short. A CME is a release of large quantities of magnetized plasma and if it strikes the Earth it can cause some serious damage to any and all electronic devices. This was also one of the most powerful CMEs in recorded history. And it blasted straight through the Earth's orbit. Luckily for us, the Earth was on the other side when that eruption occurred but due to the rotation of the Sun, had this eruption occurred just 9 days prior, we would've been engulfed by that storm. If that had happened, and there's a 12% chance that it will happen in the next 10 years, it could've taken us as much as a decade to fully recover. It's difficult to overstate the ramifications of a CME on this scale. Worldwide power outages would take weeks, months, or even years to resolve. Many satellites would have to be replaced. Electronic equipment of all kinds would cease to function seemingly over night. Medical, transportational, financial, military, national security, and other critical systems would all be compromised or destroyed. Society would grind to a halt... ...and be literally plunged into darkness for years to come. Given how dependent we've become on electricity and various technologies like the internet, it's difficult to image anything but global panic and chaos. It would not have been the end of the world but it would no doubt have felt like it. Declassified documents reveal that the US military has had over a thousand close calls with nuclear weapons since the 1950s. Over a thousand times when cataclysmic devastation was just narrowly avoided. And who knows how many near accidents the Russian military have experienced or any of the other nuclear weapon states. Coupled with the destructive power of natural events, it is truly a miracle that we've come as far as we have.