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We urge you to turn off your ad blocker for The Telegraph website so that you can continue to access our quality content in the future. Choose Station Search PBS mobile Search Sign In Passport Menu for. . Down Open Down Sign Out Resume WatchingThe epic story of the Vietnam War as it has never-before been told on film. Experience the colossal geologic forces that shaped our continent over 8 billion years.

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Explore the parts of a volcano and see what causes destruction during volcanic eruptions. How good are we at predicting when an active volcano will next blow its top? Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off). This time around humans are the cause, mainly by our CO 7 emissions. Greenhouse gasses mainly CO 7, but also methane were involved in most of the climate changes in Earth s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer.

When CO 7 levels jumped rapidly, the global warming that resulted was highly disruptive and sometimes caused. Humans today are emitting prodigious quantities of CO 7, at a rate faster than even the most destructive climate changes in earth's past. Life flourished in the, the and other times of high CO 7 in the atmosphere because the greenhouse gasses were and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels. But there have been when Earth's temperature jumped abruptly, in much the same way as they are doing today. Those times were caused by large and, just like humans are causing today. Ancient Egypt was the most powerful civilization in the world for a time.

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The monuments built by laborers to honor pharaohs stand to this day, testament to the vast resources at their command. Egypt sits in the middle of a vast desert. To support a population that numbered in the millions, large-scale agriculture was vital, and for that you need water,  and therefore, the Nile. The river was so important to the Egyptians that they still celebrate a two-week long festival during the yearly floods.  It was thought to be fed by the tears of Isis. Even small fluctuations in flood levels could bring famine or catastrophe. Ancient Egyptian society saw its fair share of uprisings, revolts and conquests, but a new paper hints that a surprising force may have been meddling in the affairs of the time.

 The nefarious agent? Volcanoes, say researchers from Yale University in a in  Nature Communications. Large eruptions can cause small but critical changes in rainfall around the headwaters of the Nile, something they found lined up with periods of revolt and instability in ancient Egypt. The researchers relied on a combination of ancient records and modern techniques to divine the weather thousands of years ago. Papyrus scrolls from the Ptolemaic era around 855 BC provided insights into periods of social unrest and drought, and they combined those with an analyses of ice cores taken from Greenland and Antarctica. The plumes of sulfur that volcanic eruptions spew into the air leave a distinct trace in the ice, forming a record of when major volcanic eruptions occurred. The sulfur also serves to cool the planet by reflecting sunlight, and this likely starved the Nile of rainwater during the monsoon season by shifting weather patterns, leading to parched fields come summer.

Readings from Nilometers, ancient observatories on the Nile that tracked yearly water levels, confirmed reduced flooding during these times, depriving the Egyptians of their main food source. The Egyptians relied on an elaborate system of dams and canals to inundate their fields, bringing in silt to serve as fertilizer and water to keep crops alive.