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The Sahara is on a regular-ish cycle going from green to desert about every 30k years. It's had multiple green eras. The last one is called the African humid pe
by culi 2y ago
The Sahara is on a regular-ish cycle going from green to desert about every 30k years. It's had multiple green eras. The last one is called the African humid period
- fuzztester 2y agoany idea why so?
- thworp 2y agoBriefly: earth‘s rotational axis had a different tilt, leading to completely different climate and weather systems behavior. Incidentally, before the green sahara period, the sahara was much larger than today.
- jjtheblunt 2y agoi've read the axis precesses completing a cycle every 24,000 years, so the fraction of ocean vs land in direct sun gradually and continually changes accordingly.
- colechristensen 2y agoThere are many higher order gravitational effects which alter earths orbit and axial tilt and therefore both yearlong and seasonal solar radiation patterns. One of these is a cyclical pattern of tens of thousands of years that caused warming and cooling somewhat less that a degree. For about six thousand years earth was half a degree warmer and weather patterns in the Sahara were different. Then there was some cooling until modern CO2 issues. In the early twentieth century there were some very real concerns about long term climate cooling as climate science was being developed but instead greenhouse gases have blasted us very far and very fast in the other direction.
- Dennip 2y agoAny idea, how does the dirt/each return over time to sustain plant life? Or is it just a gradual grow inwards with plant matter slowly forming topsoil?
- culi 2y agoThe Amazon rainforest's soil is extremely poor in nutrients and very shallow due to all the rain. In addition, at least 50% of the rain it gets comes from the trees themselves. The division between abiotic and biotic factors is a lot more fuzzy than people realize The Sahara's sand is actually full of a lot of nutrients. In fact the massive Saharan sandstorms that traverse the Atlantic Ocean are a significant source of fertilizer for the Amazon rainforest All the elements are there. You just need the right weather and plant life to get things going. Of course we can't ignore the human element. Archeological evidence suggests humans played a massive role in transitioning the Amazon Rainforest from the grassland it once was to the jungle it now is. Reforestation projects, Great Green Wall, half-moon berm projects, etc are all way way more effective than they were just a few years ago. We're learning a lot about how much humans can do to revitalize soils
- colechristensen 2y agoPioneer species that can grow on basically nothing are slowly replaced by other species as the ground builds up organic matter. Fungi play a very large part in building soil as well as big and small animals.