One of the categories of contribution considered for Geochimica et Cosmochimica Acta is a Comment. A Comment is a short manuscript which is directed specifically to a paper previously published in Geochimica. It is not a short, self-contained contribution analogous to a "Note" or "Letter" in other journals (there are no such categories for Geochimica). Instead, it focuses on the target paper, usually with the intent of disputing conclusions or interpretation, pointing out purported error or misunderstanding, challenging experimental data, or other such criticism.

A Comment must be short (equivalent to no more than four printed pages, including references, tables and figures), it may not include any new or previously unpublished data, and it may not reference any unpublished data or private communications. The principal objective of a Comment should be to improve understanding of the scientific issues at stake, and not just to register disagreement, to advocate an alternative interpretation already in the literature, or to dispute priority.

The title of a Comment must be of a standard form such as "Comment on 'The title of the previously published paper' by A. Firstauthor, B.Secondauthor, and C. So-on-and-so-forth". Otherwise, preparation of a Comment manuscript should follow the usual guidelines (in Information for Contributors) regarding format (abstract, section headings, tables and figures, etc.).

When received, a Comment will be logged and assigned to an Associate Editor. If the Editor and the Associate Editor judge that the Comment satisfies the criteria above it will be sent out for external review of scientific merit. A Comment will be evaluated by the normal criteria for a scientific contribution, except for the expectation that it will be a novel, stand-alone research contribution. An AE Report will be prepared for a Comment, just as for a research Article, and, if it is judged fundamentally satisfactory, revisions in response to review and editorial evaluation will commonly be expected before it is formally accepted for publication.

At the time a Comment is submitted, the targeted authors will be advised of receipt of the Comment and provided with a copy. At the time of the AE Report for the Comment the targeted authors will also be notified and advised that the Comment has been rejected or that revision has been invited in the expectation that a suitably revised Comment will be accepted for publication.

If the Comment is accepted for publication, the targeted authors will be invited to prepare a Response, which is the type of contribution complementary to a Comment. A Response must follow guidelines similar to those for a Comment: A Response must be short, focused on the Comment and on the underlying scientific issues, involve no new data, and cite no unpublished data or private communications. The title of the Response is also prescribed: "Response to the Comment by A. Firstcommentauthor, B. Secondcommentauthor, and T. Restofthem on "The title of the previously published paper'"".

A Response will normally not be sent out for expternal review, not will it be reviewed for scientific merit in the usual sense. It will, however, be examined by the Associate Editor and the Executive Editor to evaluate whether it follows the guidelines above, and it is possible that revisions to the Response will be requested in order to conform to the guidelines. If the revisions to the Response are found unacceptable by the Associate Editor and Executive Editor, the Executive Editor may elect to publish only the Comment.

The deadline for submission of a Response will be one month after the targeted authors are advised that the Comment has been accepted and invited to prepare the Response. If the Response is not received by the deadline, without alternative arrangements having been agreed upon in advance, the invitation will be withdrawn and the Comment sent to press without an accompanying Response.

When the Response has been received, and revised if necessary, the authors of the Comment will be provided with a copy of the Response. They may not change the Comment but they will have the option of proceeding with publication or of withdrawing the Comment. If the Comment is withdrawn, the Response also will not be published.

If both the Comment and the Response (if any) are accepted for publication they will be published together, as consecutive items in the journal. Multiple iterations will not be entertained, i.e. a "Comment on the Response to the Comment ...." will not be considered for publication.