‘The Murder of Adam and Eve’ ( 2014) by William Dietrich

Two teenagers, aged 16 and 17, are chosen by aliens to justify the existence of humanity by preventing the murder of Adam and Eve. Such a trial of poor old humanity is a common premise in science fiction. Consider the Q Continuum for one.
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That old chestnut is given a new twist in these pages by sending the pair — Ellie and Nick. — back in time to 50,000 B.C. to save themselves by saving the genetic forbearers of our species in East Africa, styled Adam and Eve.  
Nick has all the egotistical misery and self doubt of a normal teenager, while Ellie is several classes out of his league, pretty, smart, decisive, and confident. Nick is a loner with few interests.  But together they make something of a team, the more so with a box of matches, a Swiss Army knife, and few other things in their pockets when the trial began, but their greatest asset is Twenty-First Century knowledge (hygiene, maps, the wheel).
Yet for all their several advantages they have a lot to learn about living in Eden, stay downwind of the animal herds. That standing still while a lion passes in the distance is very hard when the fire ants swarm.  
They do find the genetic bearers whom they call Click and Foxy, and they do try to protect them and also get them to move toward Sinai thanks to their Twenty-First Century knowledge of maps and cross into the Middle East in time to come.  
In the course of these exertions they learn to kill, butcher, and eat, sometimes raw, wildebeest and other delights of the teeming flora and fauna. This is no place for vegetarians, vegans, lactose intolerants, etc., etc. They also learn to trust each other, and slowly win the trust of Click and his clan.  
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Woven into the story are comments, too many for this reader, about the dire straits of the environment in the Twenty-First Century and the looming environmental catastrophe that threatens the Earth.  The self-destruction of planet Earth, a perfectly good piece of real estate, is what has prompted the aliens to intervene, thinking to reset this world by extinguishing Click (Adam) and Foxy (Eve) and let evolution start over. This is a clever idea for a plot.
There are two sub-plots to muddy the water, though the major twist was evident long before its revelation. Even so it was well done.
The suspicion of my acne years that high school science teachers are not human was at last vindicated. 
Dietrich has a good ear for teen-speak though it is mercifully shorn of speech crutches of ‘like’ and ‘actually.’  Though the latter has long since migrated to adult speak.  Quarantine failed on that one.  He is even better at getting inside the mind of Nick, whose high school experiences perhaps reflect Dietrich’s own. I know they do reflect mine.
Dietrich.jpg William Dietrich who is an accomplished writer whose Nathan Gage I have much enjoyed.