Researchers from an international team led by the University of Oregon present evidence that about 2.9 billion years ago the Earth may have been almost entirely covered by ice. The key discoveries are described in a study published in Geochemical Perspectives Letters, a journal of the European Association of Geochemistry. The work underscores a dramatic chapter in Earth’s history when vast ice sheets could have stretched across much of the planet.
In a notable field finding, scientists uncovered exceptionally well preserved glacial deposits near regions tied to gold mining in South Africa. This area stands out as one of the rare locations that has remained largely unchanged since early in Earth’s history. The team describes the deposits as petrified moraines, formed when a glacier retreats and leaves behind rock fragments and debris that gradually harden into stone. These samples provide a tangible record of ancient glacier activity in a landscape that looks very different from today.
The investigators identified glacial material beneath the Witwatersrand, a region renowned for containing some of the world’s largest gold ore deposits. The site lies southwest of Johannesburg, the primary urban hub in the area. By extracting rock fragments that resembled glacial material and analyzing their isotope composition, researchers evaluated the ratios of oxygen isotopes 16O, 17O, and 18O. The masses of these isotopes influence the observed ratios, offering clues about the conditions under which the rocks formed.
Analyses revealed shifts in isotope signatures that align with glacial sedimentation. The presence of comparatively lower amounts of oxygen-18 alongside higher levels of oxygen-17 suggests deposition under subzero temperatures, a hallmark of glacier formation and ice-associated processes. These isotopic patterns help distinguish glacier-derived material from other depositional environments and bolster the interpretation of a globally significant ice event in Earth’s early history.
According to the research team, the petrified moraines found in this region rank among the oldest known examples of ancient glacial activity. The findings imply that the planet may have experienced a global or near global glaciation during this era, with a substantial portion of the surface covered by ice. The hypothesis also suggests that the area where the moraines formed was situated closer to the polar regions three billion years ago. Additional work is needed to confirm this geographic positioning and to refine the broader climate context of that era.
These results contribute to a growing body of evidence that ancient Earth underwent dramatic climatic shifts, with glacial episodes leaving enduring marks in the rock record. Ongoing multidisciplinary studies—combining field observations, isotope geochemistry, and refined dating methods—are essential to better understand the extent, duration, and global reach of these early ice ages. The attribution of the study remains with Geochemical Perspectives Letters and the researchers involved in the ongoing analysis.
Ancient scientists proposed that melting glaciers could influence atmospheric chemistry and climate dynamics, including methane release mechanisms that might amplify warming or alter greenhouse gas balances in paleoenvironments. Modern researchers continue to follow these threads to better understand how early Earth climates evolved and how such extreme conditions shaped planetary habitability over billions of years.