A host to feed off of, the right temperatures, basically the right living conditions for that type of bacteria. Most of the time it depends on the type of bacteria.
More money started rolling in
A push factor would be something like war or famine or something. A pull factor would be something like a job or new opportunity, its usually for financial reasons in my opinion. Hope this helped!
Explanation:
Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Once a rock has been broken down, a process called erosion transports the bits of rock and minerals away. Water, acids, salt, plants, animals, and changes in temperature are all agents of weathering and erosion.
