Garry Kilworth 
Split Second [EPUB ebook] 

When a young boy, Richard, goes too close to a Wiederhaus Repeater ("greatest archaeological break-through ever. Expose any prehistoric remains to it and it creates, briefly, complete hologrammatic images of the people who were in contact with them and the scenes in which they existed."), he finds himself sharing a body with Esk, a boy from the Palaeolithic era.