Right, that seems to be a strong reason to question an extraterrestrial origin. That aside, the "red rain" phenomenon is well documented in the cited paper and may be an unexplained phenomenon worthy of investigation. The red component in the rain appears to be diatom-like particles lacking DNA.

This website cites numerous historical cases of "red rain" that have been described by scientists as diatom-like particles. In a journal search at JSTOR I found two historical reports. The first (in Science, New Series, Vol. 10, No. 257, 1899) cites an 1896 report of red rain from the Australian Association for the Advancement of Science. In that case "red rain" reportedly "fell over Melbourne and much of Victoria on December 27, 1896." It notes that while the red content appeared to be volcanic-rock soil, "Under the microscope the presence of diatoms, scales of lepidoptera, quartz and granet were detected."

The second historic report I found (in Past and Present, No. 166. Feb 2000) incidentally mentions: "[...] on one occasion in 1914 he comments on a report of a shower of red rain in the Jiangsu town of Songjiang. This report was in the back pages of Shenbo, in small print, and in the local news section, all of which related to towns far away in Jiangsu and Zhejiang."

My off-the-cuff hunch is that the red diatomic cell-like component in the rain may originate from the ocean, drawn up by convection or water spouts. Many (if not all) historic cases of red rain were close to an ocean. For example, the documented cases in India were all right next to the Arabian Sea. Furthermore, in the historic cases I cite above, both Melbourne and Victoria are along the Indian Ocean, while Jiangsu runs along the Yellow Sea. ~Ian

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