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Why can shock events make radiometric dating of meteorites difficult?

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Meteorite The Hoba meteorite, lying where it was discovered in 1920 near Grootfontein, Namibia. The largest meteorite on Earth and an iron meteorite by classification, it consists of a nickel-iron alloy and is estimated to weigh about 60 tons.

Shock events complicate the radiometric dating of meteorites because they disturb the isotopic systems used to determine age.1

Radiometric dating relies on the assumption that a closed system has remained undisturbed since the time of formation or a specific thermal event. When a meteorite experiences a shock event—caused by high-pressure impacts—it can trigger localized heating or structural changes that rehomogenize or redistribute isotopes within the minerals.123

Because an isochron can represent either the time of original formation or the time when isotopes were last rehomogenized, shock-induced disturbance makes it difficult to distinguish between these events. If the isotopic ratios are sufficiently altered, the data points will no longer form a straight line on an isochron graph, rendering the system unreliable for dating. Consequently, scientists must often rely on additional evidence to determine whether a measured age reflects the object's true formation or a later resetting caused by shock or other metamorphic processes.1