What On Earth Happened? (Bloomsbury, $45) is a marvelous family present—adults will love it and they can read it with their older children. Christopher Lloyd, a science writer, has fashioned a highly readable history of Earth by time periods, employing scientific discoveries, history, religious and technological developments.  The book is illustrated with maps, photos, and gorgeous reproductions of art masterpieces. Humility is called for: scientists estimate that animals emerged onto land 400 million years ago, modern humans evolved in Africa only 130,000 years ago and spread to other continents around 50,000 years ago—and the first powered flight took place merely 100 years ago.

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