I'm looking for the title of a story about aliens which study human history.
The story is set in the distant future, where humans conquered the universe and were extinguished.
Few aliens came to Earth to get to know human history. One alien is capable of seeing history by touching things. So it tells few short stories from different human eras: prehistorical, medieval, modern and future.
All stories happend in Africa, but in different time.
First story is about early humans. Namely, aliens first visited the earth, were caught and killed by early humans.
Second story is about slave trade. The slave kills its master and became the slave trader(?)
The third story is about revolution in Africa and killing colonizers.
The forth story is about illegal dumping of radioactive waste.
The fifth is about people leaving earth because of high radioactivity.