How does the ending of Unaccustomed Earth relate to/bring closure to a larger theme of the novel?
Unaccustomed Earth ends with three related stories about Kaushik and Hema. Both are, like many of the characters in the book, children of Indian immigrants. They both break away from the expectations of their families and the larger societies, at least for a time. Hema has an affair with a married man, gets engaged to an Indian man (semi-arranged marriage), and has an affair with Kaushik. In the end, she leaves Kaushik to marry the Indian man and have his child. After the death of his mother, Kaushik is un-rooted from his father and society's expectations. He becomes a professional photographer, a vocation that allows him to keep the camera's lens between him and any real human connection. He eventually dies in the devastating tsunami that hit south east Asia but he is briefly connected to other human beings at the Thai resort he's visiting when he dies.
Lahiri took the title for the book from a quotation by Nathaniel Hawthorne:
Human nature will not flourish, any more than a potato, if it be planted and replanted, for too long a series of generations, in the same worn-out soil. My children have had other birthplaces, and, so far as their fortunes may be within my control, shall strike their roots into unaccustomed earth.
The characters struggle with rootlessness and how they fit into their new worlds, but in the end, because of their struggles and the fact that they have to find their way in "unaccustomed earth" they emerge stronger.