Exiles of Time by Nelson Bond (1948)
Nelson S. Bond (1908-2006) had a pulp career that ranged from the late 1930s to the mid 1950s, writing a number of distinctive stories while remaining lesser known than many of his contemporaries. Bond's output was spread out, publishing sports stories as well as science fiction, fantasy, and horror tales. Much of his most popular work was published in Blue Book and escaped the notice of many Sf fans. Nonetheless, Bond was named a Science Fiction Writers of America Author Emeritus in 1988 and had two posthumous retrospective collections released by Arkham House.
Bond's best-known stories are about Lancelot Biggs, about a spaceman who always manages to come out ahead. He also wrote the classic tale "Mr. Mergenthwirker's Lobblies," which became a radio series and later a television show. Among Bond's other series characters were Meg the Priestess, who appeared in three post-holocaust stories in 1939-40), Pat Pending (about a loopy inventor), Squaredeal Sam McGhee (who appeared in a number of tall tales), Horse-Sense Hank (another character who always ends out on top, despite the odds),
Bond wrote three novels in his loosely related Squared Circle trilogy*, where each novel covers one of the three ages before ours -- a concept from Mayan lore. The first of these was Exiles of Time, which appeared in the May 1940 issue of Blue Book and appeared in book form from Prime Press in 1948.
Exiles of Time is pure pulp adventure. It begins with an archaeology dig near Petra (in what is now Southern Jordan, but is described as Arabia in the book). Archaeologist Lance Vidor discovers a site that appears date from at least eight centuries before Christ, fully five centuries older than previous finds from the Nabatean civilization. More startling was Lance's discovery of a blood red brooch found in an alabaster jar: the brooch was set in aluminum, millennia before it was produced by modern man. According to the native legend, the brooch is the Nur-ed-Dam, the Light of Blood, a forbidden item that must return to the inviolable crypt from which it came. Lance and the other members of the expedition poo-poo the natives' fears. consequently, their workers attack them, killing every member of the expedition except Lance, who has found temporary shelter in the crypt. Just before his enemies are to break into the crypt, Lance has a falling sensation and blacks out.
He wakes up thousands of years in the past with others who have had the same experience at the exactly the same time. It turns out that each was holding a blood red gem when they were transported to the past. They are in a city called Spel on the ancient island of Merou and Merou is actually Mu, the legendary advanced civilization said to have sunk into the ocean in prehistory. They were brought there by Cal-thor, a scientists who had placed the blood-red stones in different areas around the world. The gems themselves had the ability to transfer whoever was holding one into the past at a specific time designated by Cal-thor
The eight million or so of Merou are the descendants of a race of Ancient Ones, long-vanished people who had scientific knowledge that has been lost to time. Cal-thor has discovered that a giant comet will strike the Earth soon, wiping out most of the population. Since his people do not have the scientific knowledge to avoid this doom, he determine to use the stones to bring back people from the future who would surely have the advanced knowledge to prevent the comet from crashing into Earth. This finely-honed plan had a fatal flaw: Civilizations rise and fall, with heights and dips, and the late 1930s era civilization that Cal-thor picked at random was not as advanced as Merou.
The world seemed doomed. But was it? Meerou's science, based on what was remembered from the Ancient Ones, was not complete. There were some things that 20th century science knew that the Merouians did not know. One of those things was that energy has mass. Using that knowledge and the Merouian science, Lance and some of the other time travelers are able to devise repellent guns that might shift the comet's orbit. For the best chance of success, the guns needed to be placed at a specific location -- the land bridge that connected the future England to the future Europe: the Bifrost Bridge in a land controlled by the Norse (whom Bond calls "Vikings"). Yep. Unless stopped, the comet will bring about Ragnarok.
To complicate matters, among the accidental time travelers are three murderous gangsters who have plans of their own. There are adventures, marvels, battles, romance, and a surprise revelation as this super-science story barrels its way along in pure pulp fashion. A great read for those willing to cast aside critical judgment.
*For those interested, the other two novels in the Squared Circle trilogy are "Gods of the Jungle" (from Amazing Stories, June and July 1942, and reprinted in Bond's 2005 posthumous collection Other Worlds Than Ours,, and 'That Worlds May Live" (from Amazing Stories, April 1943 and printed in form by Wildside Press in 2002. All three issues of Amazing Stories are available online at Internet Archive.