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The idea of three people drowning in the Sahara seems ludicrous until you consider that the Sahara hasn't always been a desert.
三个人在撒哈拉溺死的想法似乎很可笑，但仔细想想，撒哈拉并非一直都是沙漠。
In fact, it transforms from desert to lush savanna about every 21,000 years.
事实上，那里大概每隔21000年就会从沙漠变成苍翠的稀树大草原。
A quirk in Earth's planetary mechanics periodically causes its axis to tilt slightly, increasing the amount of radiation directed to the Northern Hemisphere, which in turn pulls Africa's seasonal rains northward.
地球的行星力学有个怪异之处，会过期性地造成地轴微微倾斜，使得直射北半球的辐射量增加，这又让非洲的季节雨向北移动。
For millions of years, this cycle of monsoon shifts has created numerous wet periods in the Sahara.
数百万年来，这种季风偏移的循环在撒哈拉产生很多次的丰水期。
The most recent one began at the end of the last ice age, roughly 12,000 years ago, and persisted until about 4,500 years ago.
最近的一次是始于上一个冰河时代末期，大约12000年前，持续到大约4500年前。
Technology has helped scholars see what this Green Sahara looked like.
拜科技之赐，学者现在已经能够了解这种“绿色撒哈拉”的模样。
Satellites have identified ancient riverbeds and the shorelines of lakes, including the original perimeter of Lake Chad, which at its peak was bigger than all the North American Great Lakes combined.
卫星已辨认出古代的河床和湖岸线，包括乍得湖的原始边缘，它在高峰期时比北美洲的五大湖全部加起来还要大。
But even more obvious clues about the Green Sahara have been staring scholars in the face.
不过绿色撒哈拉更明显的线索一直摆在学者面前。
Thousands of engravings and paintings discovered on rock formations throughout the Sahara document thriving hunter-gatherer communities.
在撒哈拉各地的岩层，发现了数千处雕刻和绘画，记录着兴盛的狩猎采集者群落。
The artists portrayed figures wearing elaborate headdresses and throwing spears and shooting arrows.
艺术家描绘的人物戴着繁复的头饰，投掷长矛、射出飞箭。
But their main subjects were the animals they saw, including hippos, giraffes, elephants, rhinos, and antelope -- species now more closely associated with wetter parts of Africa.
但他们主要的题材是眼中所见的动物，包括河马、长颈鹿、大象、犀牛和羚羊，如今这些物种主要分布在非洲比较多雨的地区。
Despite such vivid depictions, we know very little about these people.
尽管有这么生动的描绘，我们对那些人却知之甚少。
During the 20th century, a handful of significant archaeological sites were found in the Sahara.
20世纪，人们在撒哈拉发现了一些重要的考古遗址，
Excavations yielded samplings of pottery and stone tools -- isolated glimpses of Green Sahara cultures.
发掘出的少量陶器和石器，这些个别的发现让人得以一窥绿色撒哈拉的不同文化。
But for the most part, the desert's intense radiation, high winds, and shifting sands have scattered, buried, and scoured away much of the evidence of their existence.
但整体来说，沙漠的强烈辐射、强风和流沙，早已让这些文化存在的多数证据四散各处、遭到掩埋和侵蚀。
So it was practically a miracle when Paul Sereno stumbled upon Gobero.
因此，保罗·塞雷诺意外发现格伯托简直是个奇迹。
He's an unlikely scientist to find a human burial ground, as his primary subjects lived millions of years before humans.
他这样的科学家其实不太可能发现人类墓地遗址，因为他的主要研究对象的生存时期比人类早了好几百万年。
Since the early 1990s, the University of Chicago paleontologist and National Geographic Explorer has made headlines for his discoveries of new dinosaur species in the Sahara,
从20世纪90年代初期至今，这位芝加哥大学古生物学家、国家地理探险家好几次登上新闻头条，因为他在撒哈拉发现了一些新种恐龙，
including Afrovenator, a fast-running meat-eater; Suchomimus, a creature the length of a school bus, with a crocodile-like head; and Jobaria, a 70-foot-long plant-eater with an elongated neck.
其中包括非洲猎龙，一种跑得飞快的食肉恐龙；以及似鳄龙，体长像一辆校车、头部像鳄类的恐龙；还有约巴龙，体长70英尺的食草恐龙，有着细长的颈部。
In 2000, Sereno was looking for more of their kind as he led a scouting expedition in the Ténéré.
2000年，塞雷诺带领一个搜索远征队去泰内雷沙漠，想要寻找更多的新种恐龙。
The team spent one morning driving in a convoy of Land Rovers near a rocky ridgeline. Periodically, they'd stop to search on foot for fossils.
有一天，团队的路虎车队在一条岩石棱脊附近开了一上午的车，每隔一阵子就停下来，以步行方式寻找化石。
Just as the convoy was about to return to camp, Mike Hettwer, the expedition's photographer, wandered toward three small dunes.
就在车队准备回营地时，远征队的摄影师麦克·黑特维缓步走向三座小沙丘。
He found them covered with human bones, potsherds, arrowheads, and other stone artifacts. "It was all there just lying on the sand," he told me, "everywhere you looked."
他发现那里满地都是人类骨头、陶器碎片、箭头和其他古代石器。“全都躺在那里的沙子上，”他对我说，“放眼望去都是。”
Bido Dindine, one of the expedition's Tuareg guides, said local camel herders referred to the area as Gobero.
远征队的一位图阿雷格部族向导毕多·丁迪内说，当地养骆驼的人称这里为格伯托。
There were also lots of animal bones. Paleontologists study modern species to understand dinosaur physiology, and Sereno has a near-encyclopedic memory for animal skeletons.
这里还有大量的动物骨头。古生物学家会研究现代的物种，以便了解恐龙的生理学，而塞雷诺对动物骸骨的记忆有如百科全书。
He quickly recognized the bones of hippos, giraffes, fish, crocodiles, and turtles. "All the animals we find in the Serengeti were there," he said.
他很快就认出河马、长颈鹿、鱼类、鳄鱼和龟类的骨头。“我们在塞伦盖蒂地区发现的所有动物，这里都有。”他说。
Next to the dunes they found a dry lake bed, which helped explain the large concentration of aquatic animals.
他们在沙丘旁边发现一个干涸的湖床，有助于解释大量聚集的水生动物。
"There was so much to take in," Sereno said. "It was overwhelming."
“有好多事要理解，”塞雷诺说，“信息量太大了。”
They made a quick survey, estimating that the area contained upwards of 200 burials.
他们很快检视一番，粗估这个地区有超过200座坟墓。
Eventually, Sereno came to understand that the three dunes were protected by a doughnut-like rim of rhizoconcretions, a type of rock formed around the roots of reeds and other plants.
最后塞雷诺了解到，这三座沙丘被一圈甜甜圈状的“根结核”保护，这是一种岩石，会出现在芦苇和其他植物的根部周围。
This created a protective crust that kept the dunes intact. When the rhizoconcretions finally started to break apart, the skeletons had begun to emerge.
这会产生一种保护壳，让沙丘保持完整。等到根结核终于开始破裂，骸骨就渐渐暴露出来。
There were half-buried skulls, hands reaching out of the sand, ribs scattered.
有半埋着的头骨、从沙里伸出来的手，肋骨散落一地。
"The rhizoconcretions are why those burials survived thousands of years," Sereno said, noting the seasonal Harmattan winds, which carry Saharan dust across West Africa to the Atlantic. "Any exposed bones won't last long."
“根结核是这些墓葬能保存数千年的原因。”塞雷诺说。他指出，季节性的哈麦丹风会带着撒哈拉的尘土越过西非抵达大西洋。“只要骨头暴露出来，都撑不了太久。”
He showed me a photo of a skull from the 2000 trip and another photo of it in the same spot five years later. Much of the bone had been ground away -- literally sandblasted.
他给我看了2000年那趟行程拍摄的一张头骨照片，以及五年后在同一地点拍摄的另一张照片。骨头大部分都已经磨蚀掉，其实就等同于被喷砂研磨掉了。
"That's what the desert does," Sereno said.
“那是沙漠做的好事。”塞雷诺说。
