Why can quartz sand with beryllium-10 reveal how fast a whole river basin erodes?
Show answer & explanation
Answer: Surface-exposure clock
Rainfall chemical tag — Not quite. Rain matters for erosion, but beryllium-10 in quartz is not mainly a rain gauge. It accumulates when minerals sit near the surface under cosmic-ray exposure, then river sand mixes grains from across the basin. That makes it a time-integrated erosion signal rather than a simple record of storm chemistry.
Direct fault-slip timer — Almost, but this method does not date fault slip directly. A fault can influence erosion, and the erosion then changes how long quartz grains remain near the surface. The isotope is therefore an erosion clock for the landscape, not a stopwatch attached to the fault plane.
Surface-exposure clock ✓ — Right. Cosmogenic beryllium-10 builds up in quartz exposed near Earth’s surface, so fast erosion gives grains less exposure time and lower concentrations. River sediment mixes material from hillslopes across a basin. That is why the Science study could compare 1,744 basin-scale erosion-rate measurements worldwide.
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