Sahara desert

Discussion in 'Earth Science' started by timojin, Dec 29, 2016.

  1. timojin Valued Senior Member

    How long ago the sahara was not a desert, what was the cause of desertification ?
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  3. sculptor Valued Senior Member

    sahara was green, then we had a cold snap @5kybp ---preserved otzi and desertified sahara
    guess away
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  5. timojin Valued Senior Member

    Was it the the tilt in the axle ?
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  7. iceaura Valued Senior Member

  8. sculptor Valued Senior Member

    That is one theory put forward. (just one degree of difference.)
    The cold snap seemed global with evidence in south america, europe africa and asia(that I've read about)

    If we go with change in tilt----------What caused it?
  9. timojin Valued Senior Member

    It all depends which period we look into. see.

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    View of the Great Sand Sea of Egypt from the Gilf Kebir Plateau. This was a good place to live 8000 years ago.
    Credit: © Science
    At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.

    During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.

    The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.

    When the rains came

    Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.

    But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.

    This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.

    "The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.

    Frolicking in pools

    In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.

    Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.

    In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.

    "Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.

    A timeline of Sahara occupation [See Map]:

    • 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
    • 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
    • 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
    • 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
    youreyes likes this.
  10. youreyes amorphous ocean Valued Senior Member

    What caused the monsoon rains to sweep into Sahara? Volcanic eruptions?
  11. timojin Valued Senior Member

    Wo bist do , lange zeite habe ich nicht gehort from dir.
    I believe the volcano are at the north , The monsoon were due to the earth tilt
  12. Fraggle Rocker Staff Member

    This is the only source I've found that discusses the shift in the Earth's axis. I have no idea if this is a respected publication (although I have encountered it before and generally find it to be sensible), so I'm only offering it for your interest. I'm not saying that it is true.
  13. Ophiolite Valued Senior Member

    The original article, from Geophysical Research Letters, may be found here, in full. The paper has been cited by 526 other authors, including 90 in the last four years. This suggests a paper that was well received and that, despite being sixteen years old, is still thought to contain information of value. (Note, however, that I have not checked the 526 citations to determine the attitude to the paper.)

    Note that the axial tilt is only one element in the mechanism. Equally important is the position of perihelion in relation to Northern Winter. As noted the abrupt change in climate is related to terrestrial feedback mechanisms. (And provides further evidence for why climate alarmists are alarmed. Shit happens fast when it hits the fan.)

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