There are likely many undiscovered impact structures on Earth, but several challenges
prevent their detection, including possible concealment beneath large ice sheets. In recent
years, geophysical, geochemical, and microphysical evidence has mounted for a ca. 58 Ma
impact structure under the Hiawatha Glacier, northwest Greenland. Here, we report evidence for a second, much older hypervelocity impact event in this region, recorded in an
impact melt rock sample collected from a glaciofluvial deposit in Inglefield Land. Secondary ion mass spectrometry U-Pb analyses of shock metamorphosed zircon grains yielded a
previously unrecorded, Proterozoic best estimate impact age of 1039 ± 16 Ma (mean square
of weighted deviates = 2.9). Based on Archean–Proterozoic target rock U-Pb ages obtained
from unshocked zircon grains and the location of the melt rock sample along the ice margin,
we suggest this sample was derived from a hypervelocity impact structure farther inland,
concealed by the Greenland Ice Sheet. This study demonstrates the ability to uncover new
impact events in some of the most inaccessible areas on Earth and the possibility of sampling
multiple impact structures from one location when examining ex situ material. Our results
have implications for current and future Martian and lunar returned samples that demonstrably bear complex impact histories.