Gail Simone 
Catalyst Prime: Seven Days Vol. 1 [PDF ebook] 

The meteors that fell to Earth two years ago and gifted people with enhanced abilities were only the beginning. Now the source of those meteors has returned to finish the job and finish humanity off for good. His name is Khrelan and he’s given humanity seven days to make their peace before he terraforms the Earth to suit his needs killing all of humanity in the process. New and old heroes join forces to stop Khrelan, but even if he’s defeated, what will be left in the aftermath? Seven days to live, what does humanity choose to do with them?