Unit 5 Canada—“The True North”:85张PPT
Unit 4 Astronomy the science of the stars:77张PPT
Unit 3 The Million Pound Bank Note:82张PPT
Unit 2 Healthy eating:82张PPT
Unit 1 Festivals around the world:96张PPT
(2019·蚌埠高三第二次质检)A new study suggests climate conditions in the Sahara Desert, one of the hottest, driest and most deserted areas in the world, have changed from wet to dry about every 20, 000 years.
But previous evidence has suggested the Sahara did not always experience such extreme heat and dry conditions.At times, the Sahara changed to a very wet climate.This permitted plants and animals to develop and grow and led to the creation of human settlements.Now, the researchers have discovered more evidence, which, the lead researcher David McGee says, supports the idea that the Sahara’s climate kept changing between wet and dry about every 20, 000 years.
McGee reported these climate changes were mainly driven by changes in the Earth’s axis(地轴) as the planet travels round the sun.This process affects the amount of sunlight between seasons.Every 20, 000 years the Earth receives more strong summer sunlight.When the Earth’s axis changes again, the amount of sunlight is reduced.This season change happened continuously every 20，000 years.The other part of the season produced rainy conditions, resulting in a wetter, greener, plant-rich environment.When the rainy activity weakens, the climate becomes hot and dry, like the Sahara remains today.
Unit 1 Festivals around the world.ppt
Unit 1 新题培优练.doc
Unit 2 Healthy eating.ppt
Unit 2 新题培优练.doc
Unit 3 The Million Pound Bank Note.ppt
Unit 3 新题培优练.doc
Unit 4 Astronomy the science of the stars.ppt
Unit 4 新题培优练.doc
Unit 5 Canada—“The True North”.ppt
Unit 5 新题培优练.doc