(b) the hematite spherules have uniform internal structures. The diagenetic transformation (i.e., change by water-rock interactions) to today's sediments involved a significant shift in water flows in the region. The inflows from rivers became less, and the dominant water movements in the sediments became vertical with rising and falling aquifer levels. At least one model of global Martian hydrology accounts for the historical shift in water flows at Meridiani Planum. This model links Meridiani's change in water flows to activity in the volcanic Tharsis region. With the vertical aquifer flows, it is believed that (playa) lakes repeatedly formed and disappeared as the aquifer levels rose and fell.Squyres, S. et al. 2004. "The Opportunity Rover's Athena Science Investigation at Meridiani Planum, Mars". Science: 306, 1698-1703. https://doi.org/10.1126/science.1106171 (The dry area around Utah's Great Salt Lake is a playa.) McLennan and his students constructed a geochemical model that generates hematite within a context like the Meridiani sediment.Hurowitz, J. A., Fischer, W. W., Tosca, N. J., and Milliken, R. E., 2010, "Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars," Nature Geoscience, 3, 323–326. https://doi.org/10.1038/NGEo831 The hematite formed into spherules by concretion (when minerals came out of solution). The concretion process to form spherules of hematite probably occurred by diffusion of the hematite through the sedimentary rock matrix. Formation of Soils & Loose Spherules, Crater Degradation The period of rising and falling aquifer levels ceased, and no water flowed on Meridiani Planum thereafter.Golombek, M. P., Warner, N. H., Ganti, V., Lamb, M. P., Parker, T. J., Fergason, R. L., and Sullivan, R., 2014, "Small crater modification on Meridiani Planum and implications for erosion rates and climate change on Mars." J. Geophys. Res.: Planets, 119, 2522–2547. https://doi.org/10.1029/2014JE004658 Although, when this happened is poorly understood. Estimates include around 3.5 billion years ago and about 3 billion years ago. The only water left at the plain is bound in rocks. Erosion with water flows in earlier eras was much faster than in this arid epoch. However, erosion did not stop. Other much slower erosional processes continued and became the primary agents of change to the plain. This slower change was and is driven by meteorite impacts, the wind, and gravity. Over the hard-to-grasp eon of around three billion years, meteorite impacts and the wind formed the sandy top soils and loose hematite spherules and sorted these into the layered soil bedforms that