Impact-related environmental catastrophe contributed substantially to the extinction of North American megafauna at the terminal Pleistocene.

The extinction window (roughly two millennia at current resolution) cannot isolate any instantaneous event; the claim is not testable at the precision it asserts, and nothing currently favors impact over climate, hunting, or combinations.

The claim that an impact contributed to megafaunal extinctions is weakly supported. Although the extinctions occurred broadly around the Pleistocene-Holocene transition, the temporal resolution of the die-off spans millennia (roughly 13.8–11.4 ka) rather than a single event horizon. The strongest opposing consideration is that the extinction interval overlaps with severe climate oscillation and human arrival, providing well-attested terrestrial mechanisms for the die-off without requiring an instantaneous catastrophe.

The extinction of ~35 North American megafaunal genera in a terminal Pleistocene window is established (YDIH‑C008), and the interval broadly overlaps the Younger Dryas, so an impact contribution is not prima facie impossible. However, last‑appearance chronologies only constrain extinctions to a ~2,000‑year span (~13.8–11.4 ka), far too coarse to isolate a short‑lived impact aftermath, and the same window also contains substantial climatic change and human expansion that are independently plausible drivers. The strongest opposing consideration is that no unambiguous kill mechanism or mortality evidence (e.g., blast or burn damage in situ at the boundary) has been demonstrated despite two decades of focused impact‑oriented work.

The extinctions are real and overlap the Younger Dryas transition, but last-appearance dates confine the die-off only to a roughly two-thousand-year window that also contains human expansion and severe climate oscillation. No published chronology isolates an instantaneous event, and no independently scrutinized kill-mechanism evidence exists at the boundary. The strongest opposing consideration is that Faith and Surovell's analysis is statistically consistent with a geologically concentrated pulse rather than a long staggered decline, which a sudden catastrophe could in principle produce. Concentration at millennial scale is equally predicted by climate and hunting accounts.

The extinctions are real (C008, established) and broadly overlap the onset, which is the claim's only positive evidence — and it is evidence every rival hypothesis also predicts. The best chronology confines the die-off to a roughly two-millennium window that also contains human expansion and severe climate oscillation, and no burn- or blast-associated mortality horizon at the boundary has survived scrutiny. With the parent's physical evidence failing, bare temporal consistency cannot carry "contributed substantially." Strongest opposing consideration: the resolution limit is symmetric — current dating can no more exclude a rapid impact-driven contribution than establish one — so "contradicted" would overreach the evidence as much as strong support would.

The extinctions are real and geologically concentrated, but Faith and Surovell's own framing puts the resolved interval at roughly 13.8–11.4 ka calibrated, which cannot isolate an instantaneous event and equally accommodates climate change and human predation. No kill-mechanism evidence at the boundary survives independent scrutiny in these records. The strongest opposing consideration is Signor-Lipps bias: last-appearance dates systematically postdate nothing and predate true extinction, so a genuinely abrupt terminal event could be smeared by sampling. Even granting that, the claim has no positive discriminating support, and it inherits the weakness of the impact claim it depends on.

The extinction window is roughly two millennia at current dating resolution (YDIH-E025), which cannot isolate any instantaneous event; nothing currently favors impact over climate, hunting, or combinations.

The extinction window resolvable from last-appearance dates spans roughly two millennia (YDIH-E025), which cannot isolate any instantaneous cause. Nothing in the record favors impact over climate change, human predation, or their combination.

The extinction window resolvable from last-appearance dates spans roughly two millennia (YDIH-E025), which cannot isolate any instantaneous cause. Nothing in the record favors impact over climate change, human predation, or their combination.

The extinction interval resolvable from last-appearance dates spans roughly two millennia (YDIH-E025), which cannot isolate any instantaneous cause. Nothing in the current record favors impact over climate change, human predation, or their combination.

The extinction window resolvable from last-appearance dates spans roughly two millennia (YDIH-E025), which cannot isolate any instantaneous cause. Nothing in the record favors impact over climate change, human predation, or their combination.

The extinction window resolvable from last-appearance dates spans roughly two millennia (YDIH-E025), which cannot isolate any instantaneous cause. Nothing in the record favors impact over climate change, human predation, or their combination.

The extinctions are real and broadly overlap the Younger Dryas transition, but the dated record resolves the die-off only to an interval of roughly two millennia (~13.8–11.4 ka calibrated) — far too coarse to isolate an instantaneous event, and equally compatible with climate change, human hunting, and interacting causes.

Last-appearance data for North American megafauna define a broad extinction window spanning roughly two millennia rather than an instantaneous extinction horizon coinciding with a 12.8 ka impact. Taphonomic constraints like the Signor-Lipps effect preclude resolving these extinctions to an abrupt bolide catastrophe, and archaeological continuity undermines the presence of an environmental collapse. The strongest opposing consideration is Faith and Surovell's demonstration that megafaunal extinctions were geologically concentrated in the terminal Pleistocene rather than a gradual decline across the entire late Quaternary.

The extinction itself is real (YDIH-C008), but the impact attribution has no surviving direct support: the shocked-quartz paper that most directly claimed the link was retracted in 2026, and Holliday et al. 2023 conclude the consequences are explained by conventional processes. The strongest opposing consideration is that a geologically concentrated extinction window (13.8–11.4 ka in Faith & Surovell) is compatible with a sudden event and cannot exclude a contributing impact — but compatibility is not evidence of contribution.

YDIH-E025 supports a geologically concentrated North American extinction interval, but its roughly two-millennia resolution cannot place the extinctions at a proposed instantaneous event or measure impact causation. No supplied record directly estimates how much an impact-related catastrophe contributed relative to other processes. The strongest opposing consideration is the broad temporal overlap between extinctions, the Younger Dryas transition, and claimed proxy horizons, which keeps the attribution possible without supporting the word "substantially."

While megafaunal genera did disappear in a geologically concentrated terminal-Pleistocene window, no evidence links that loss to impact-related catastrophe; last-appearance data lack the resolution to isolate a 12.8 ka event, and conventional human and climatic stressors suffice. Strongest opposing consideration is the temporal coincidence within broad uncertainties, but coincidence is not causation and the predicted catastrophic signature is absent.

The ledger's only specified pathway from impact to extinction is an environmental catastrophe of hemispheric burning and impact winter (E005, E017). That catastrophe fails its independent test (E016, E018), and the impact itself lacks diagnostic support (C011) and secure isochrony (C010). The concentrated extinction of E025 spans roughly 13.8–11.4 ka, a window that cannot separate a 12.8-ka horizon from other terminal-Pleistocene causes, and the black mats draping the last in-place remains are wetland facies (E014). Confidence is low because no record tests extinction timing against the horizon at decadal resolution or demonstrates an alternative cause; the contradiction runs through the claim's upstream premises, not through extinction data. Strongest opposing consideration: megafaunal last appearances do coincide with the Younger Dryas onset at coarse resolution, and nothing in the ledger excludes an impact contribution if a sufficiently energetic event occurred.

The extinctions are real and broadly overlap the Younger Dryas transition, but the dated record resolves the die-off only to an interval of roughly two millennia (~13.8–11.4 ka calibrated) — far too coarse to isolate an instantaneous event, and equally compatible with climate change, human hunting, and interacting causes.