well i can say for sure that it dose not steadily increase. the troposphere gets colder as you ascend so its the exterior temperature slowly decreases. (apex)
You cant settle in deserts due to lack of water and scarcity of food, which led to the Saharan regions being less populated. Hope this helps.
Each follows a different text and all were founded at different times.
Judaism follows the Torah and was created in 1800 BCE.
Christianity follows the Bible and was created in 33 CE.
Islam follows the Qur'an and was created in 610 CE.
