The Vikings were present in North America in 1021 CE, according to a radiocarbon study that analyzed wooden artifacts recovered from an archaeological site in Newfoundland (Nature 2021, DOI: 10.1038/s41586-021-03972-8). The investigation used site artifacts known to have belonged to the Vikings to pinpoint when Europeans traversed the Atlantic Ocean, which marks the beginning of the time that knowledge and biological material could have been exchanged between Europe and the Americas. Researchers have long known that about 1,000 years ago, Norse seafarers settled on the northern peninsula of Newfoundland at a site known as L’Anse aux Meadows. Reported estimates of the timing of this activity vary from 793 to 1066 CE. To narrow that time window, a team led by Margot Kuitems and Michael W. Dee of the University of Groningen used an accelerator mass spectrometry method to measure carbon isotope ratios in wooden artifacts that had been modified by metal tools—which Indigenous inhabitants did not use at that time. They analyzed the data in combination with an independently established feature in the atmospheric 14C record. The feature makes it possible to identify a wooden artifact’s annual tree ring that formed in 993 CE because of a cosmic-ray event that year that abruptly raised 14C levels in those rings. The data show that the trees from which the artifacts were made were cut in 1021 CE.