Nanodiamond-rich layers, including reported hexagonal lonsdaleite, occur in Younger Dryas boundary sediments at multiple sites.

Reported repeatedly by proponent teams; the diagnostically crucial lonsdaleite identification was specifically rejected by independent TEM specialists, and no blinded confirmation exists.

The presence of boundary-layer nanodiamonds, especially lonsdaleite, is mixed. While proponents report their presence, independent crystallographic re-evaluations found no nanodiamonds and argued the supposed shock-diagnostic hexagonal forms were misidentified graphene aggregates. The strongest opposing consideration is that proponents continue to assert their recovery using different preparations, leaving the proxy in a state of unstandardized methodological dispute.

Proponent teams have reported nanodiamond‑rich layers, including claimed lonsdaleite, at Younger Dryas boundary horizons (YDIH‑E010), which, if confirmed and shock‑formed, could be impact‑ relevant. However, independent TEM work by Daulton et al. failed to find nanodiamonds in tested YD sediments and argued that particles called lonsdaleite were instead stacked graphene‑like aggregates (YDIH‑E011), directly challenging the most diagnostic aspect of the proxy. The strongest opposing consideration is that Daulton et al. sampled only some sites and preparations, so it remains possible that nanodiamonds exist at other localities or under different methods, but boundary specificity and lonsdaleite identification are clearly not established.

Kennett and colleagues reported cubic and hexagonal nanodiamonds in boundary sediments in Science, while Daulton and colleagues found no nanodiamonds in tested Younger Dryas sediments and concluded purported lonsdaleite was misidentified graphene-family aggregates. Later proponent reports keep the existence question open, so a blanket negative would overstate the record. The strongest opposing consideration is that genuine shock-formed lonsdaleite would be strong impact evidence and proponents argue other sites and preparations still show diamonds. The diagnostically crucial hexagonal identification has never been independently confirmed, and the 2016 blind test reported very low or absent nanodiamond abundance at the boundary.

The existence claim is directly contested at the specialist level: proponent teams reported nanodiamonds including shock-diagnostic lonsdaleite in Science, and independent transmission-electron-microscopy specialists re-examined such material, found no diamonds, and offered a specific misidentification mechanism — stacked graphene/graphane-family sheets rather than hexagonal diamond. Later proponent reports at other sites keep the question alive, and no blinded split-sample TEM study with pre-declared identification criteria has ever been run. Strongest opposing consideration: the independent negative is itself site- and preparation-specific, so "nanodiamonds never occur" would overstate the case — but the diagnostically crucial lonsdaleite identification has never been independently confirmed, which is why this is mixed rather than supported.

The affirmative report is a one-page Brevia whose identification evidence lives in supplements; against it, independent TEM and electron-diffraction specialists found no nanodiamonds in tested Younger Dryas sediments and concluded the shock-diagnostic hexagonal phase was misread stacked graphene-family sheets, and the blind test likewise found nanodiamond abundance low or absent at the boundary. The diagnostically crucial part of the claim is therefore the part that failed independent scrutiny. The strongest opposing consideration is that Daulton et al. tested particular sediments and preparations, so their negative does not automatically generalize, and later proponent reports at other sites keep the existence question formally open. Blinded, criteria-locked TEM on shared splits has never been done.

Repeatedly reported by proponent teams (YDIH-E010), but independent TEM specialists found no nanodiamonds and rejected the diagnostically crucial lonsdaleite identification (YDIH-E011); no blinded confirmation exists.

Proponent teams report nanodiamonds at multiple sites (YDIH-E010), but independent TEM and electron diffraction found none in the tested sediments and rejected the diagnostically crucial lonsdaleite call (YDIH-E011). No blinded confirmation exists, and the 2016 blind test also found little (YDIH-E009).

Proponent teams report nanodiamonds at multiple sites (YDIH-E010), but independent TEM and electron diffraction found none in the tested sediments and rejected the diagnostically crucial lonsdaleite call (YDIH-E011). No blinded confirmation exists, and the 2016 blind test also found little (YDIH-E009).

Proponent teams report nanodiamonds at multiple sites (YDIH-E010), but independent TEM and electron diffraction found none in the tested sediments and rejected the diagnostically crucial lonsdaleite identification (YDIH-E011). No blinded confirmation exists, and the 2016 blind test also found little (YDIH-E009).

Proponent teams report nanodiamonds at multiple sites (YDIH-E010), but independent TEM and electron diffraction found none in the tested sediments and rejected the diagnostically crucial lonsdaleite call (YDIH-E011). No blinded confirmation exists, and the 2016 blind test also found little (YDIH-E009).

Proponent teams report nanodiamonds at multiple sites (YDIH-E010), but independent TEM and electron diffraction found none in the tested sediments and rejected the diagnostically crucial lonsdaleite call (YDIH-E011). No blinded confirmation exists, and the 2016 blind test also found little (YDIH-E009).

Reported by proponent teams in Science and later papers; directly contradicted by independent transmission-electron-microscopy work that found no nanodiamonds in tested Younger Dryas sediments and disputed the lonsdaleite identification specifically. Later proponent reports keep the dispute alive; "nanodiamonds never occur" would overstate the negative case, but boundary specificity and identification both remain contested.

Independent transmission electron microscopy and electron diffraction investigations failed to detect nanodiamonds in boundary sediments and demonstrated that reported hexagonal lonsdaleite crystals were misidentified graphene and graphane aggregates. Furthermore, blinded testing across stratigraphic sections found negligible nanodiamond counts at the target horizon. The strongest opposing consideration is Kennett et al.'s initial report of cubic and hexagonal diamond allotropes within boundary sediments across multiple North American localities.

The claim rests on an unresolved identification dispute: Kennett et al. 2009 reported cubic and hexagonal nanodiamonds at multiple sites, while Daulton et al. 2010's specialist TEM work found none and reidentified the diagnostically crucial lonsdaleite as graphene-family aggregates, and the 2016 blind test found nanodiamond abundance at the boundary very low or absent. The strongest opposing consideration is that Daulton tested specific sediments and proponents argue other sites and preparations still show diamonds — but the shock-diagnostic form has never been independently confirmed, so the claim as stated (including lonsdaleite) cannot be accepted, while a flat contradiction would outrun the tested localities.

YDIH-E010 reports nanodiamonds, including claimed hexagonal forms, at multiple boundary localities, while YDIH-E011 found no nanodiamonds in its tested sediments and concluded that the purported lonsdaleite was misidentified graphene-family material. The negative study directly addresses the most diagnostic identification but does not sample every locality used in the positive reports. The strongest opposing consideration to a negative judgment is that later or differently prepared sites could contain genuine cubic nanodiamonds; however, the supplied evidence does not independently confirm the claimed lonsdaleite.

Proponent reports describe nanodiamond-rich layers including hexagonal forms at multiple sites, yet independent TEM and electron diffraction find no diamonds and re-identify purported lonsdaleite as graphene/graphane aggregates; later proponent claims at other sites keep existence open while the shock-diagnostic form remains unconfirmed. Strongest opposing consideration is the possibility that preparation differences allow genuine diamonds to be recovered under some protocols.

Kennett et al. 2009 reported cubic and hexagonal nanodiamonds in the boundary layer at multiple sites (E010). Independent transmission-electron-microscopy and diffraction work found no nanodiamonds in the tested sediments and reinterpreted the putative lonsdaleite as graphene/graphane-family aggregates (E011). The blinded two-laboratory test reported very low or absent nanodiamond abundance at the boundary (E009). The shock-diagnostic hexagonal form has no independent confirmation anywhere in the ledger, and the supporting record is a one-page report whose identification evidence sits in contested supplements. Strongest opposing consideration: Daulton et al. tested specific sediments and the blind test was essentially one site, so the negatives do not automatically generalize to other localities where proponents report diamonds.

Reported by proponent teams in Science and later papers; directly contradicted by independent transmission-electron-microscopy work that found no nanodiamonds in tested Younger Dryas sediments and disputed the lonsdaleite identification specifically. Later proponent reports keep the dispute alive; "nanodiamonds never occur" would overstate the negative case, but boundary specificity and identification both remain contested.