Question

For decades, planetary scientists accepted the Late Heavy Bombardment (LHB) as a foundational event in early solar system history. According to this hypothesis, a sudden spike in asteroid impacts battered the Moon and inner planets approximately 3.9 billion years ago, long after the initial period of planetary accretion. Proponents of the LHB pointed to the clustered ages of lunar impact melts brought back by Apollo missions as primary evidence of this cataclysmic surge.

However, modern critics argue that this apparent spike is merely an artifact of sampling bias. Because all Apollo landing sites were concentrated on the lunar near side, close to the massive Imbrium Basin, the samples collected may simply reflect the age of that single, widespread impact event rather than a global bombardment period. If the Apollo melts are dominated by Imbrium ejecta, the clustered ages do not demonstrate a prolonged spike in impacts across the entire Moon.

Advocates of the LHB counter this objection by highlighting chemical signatures in the lunar samples. They note that the concentrations of highly siderophile (iron-loving) elements vary significantly among different impact melt groups, suggesting they originated from distinct impactors rather than a single, homogeneous sheet of Imbrium ejecta. Yet, this rebuttal is itself challenged by recent dynamical simulations of planetary migration, which show that a late, sudden disruption of the asteroid belt is statistically highly improbable. Ultimately, while the chemical diversity of the melts complicates the singular-impact theory, it is insufficient to rescue the LHB from the growing body of orbital evidence against it.

Based on the passage, the reference to 'chemical signatures' serves primarily to do which of the following?