Relatives of modern humans inhabited Britain at least 840,000 years ago, more than 100,000 years earlier than archaeologists previously believed, researchers reported Tuesday.

The find surprised scientists because most believed that the hominids, bred on the sweltering plains of Africa, could not readily survive in the colder climate of Ice Age Britain. Even though Britain was in the midst of a warming period at the time, winter temperatures were still five to six degrees Fahrenheit colder than now, which would have made survival a challenge for species not adapted to it.

“We really didn’t think early humans could cope with those kinds of environments,” archaeologist Nicholas Ashton of the British Museum said at a news conference. Ashton is a co-author of the paper published in the journal Nature. Prior to this discovery, researchers didn’t believe hominids had reached north of the Pyrenees and the Alps by that time.

The discovery is based on 78 flint tools that researchers found on the English coast of Norfolk near the village of Happisburgh, about 20 miles from Norwich. The presence of the tools was originally revealed by coastal erosion.

Researchers also found an abundance of fossilized bones and coprolites (fossilized dung), indicating that the region was rich in mammoths, hyenas and saber-toothed cats, among other species. The tools were probably used to process the meat and hides from animals killed by predators and abandoned by the hyenas.

The site is just north of what was then a land bridge connecting Britain to the continent. Hominids migrating northward from the Mediterranean region are known to have crossed the land bridge many times: At least nine separate hominid colonizations have now been documented, with eight of the groups dying out.

No hominid skeletons have been found, but researchers believe the inhabitants were most likely Homo antecessor, a species that was predominant in Spain about the same time. H. antecessor is a branch of the human tree that ultimately went extinct.

The artifacts are too old for radiocarbon dating. Researchers determined their age by examining paleomagnetism in the soil, which indicates reversals of the Earth’s magnetic field, and by the appearance of fossils whose extinction has been previously dated.

“The case is not absolutely watertight, but it is pretty good,” wrote paleomagnetics expert Andrew P. Roberts of the Australian National University in Canberra in an editorial accompanying the paper. “The collective evidence strongly indicates that this is the oldest northern European site occupied by humans.”

thomas.maugh@latimes.com