The promise of jobs and prosperity, among other factors, pulls people to cities. Half of the global population already lives in cities, and by 2050 two-thirds of the world's people are expected to live in urban areas. But in cities two of the most pressing problems facing the world today also come together: poverty and environmental degradation.
"Memory Cells", are cells responsible for remembering what and how to fight off a specific pathogen. When a memory cell is produced for a specific pathogen, you are granted long lasting immunity.
It’s part of the upper mantle just below the lithosphere. Rocks in the asthenosphere are “plastic” meaning they can flow in response to deformation (like silly putty). It’s highly viscous, mechanically weak and ductilely deforming region of the the upper mantle.