Unravelling the ‘blood rain’ mystery

Since 1896, reports have been coming in of sporadic instances of red coloured rain over parts of Kerala and Sri Lanka.

Updated - April 03, 2015 07:28 am IST

Published - April 01, 2015 11:50 pm IST

The blood rain phenomenon was reported from Kerala, Sri Lanka.

The blood rain phenomenon was reported from Kerala, Sri Lanka.

A recent study by Indian and Austrian scientists has led to the discovery of the cause of the ‘Blood Rain’ phenomenon to be dispersal of spores of micro algae. Since 1896, reports have been coming in of sporadic instances of red coloured rain over parts of Kerala and Sri Lanka. The latest one was in 2013 over Kerala.

The rain colours red even laundry left in the open to dry and reminds one of human blood. Many reasons were attributed to this mysterious phenomenon — some irrational — like a divine spell, and alien involvement. The Huffington Post reported in 2012 that this was caused by extraterrestrial life (aliens).

The recent study, published in the journal Phylogenetics and Evolutionary Biology , confirmed that the red colour in the rain was caused by the presence of spores of a European species of green microalgae, Trentepohlia annulata that was reported previously only from Austria —a Central European country.

The study confirmed that the blood rain is nothing but a mechanism employed by this alga to disperse its spores (similar to plant seeds) to a very large area at once, so that algae can quickly colonize a large area. The study revealed that DNA sequence of this species from Kerala and that from Austria had very little differences — and they evolve slowly, which suggests that the alga got introduced from Europe not very long ago. “The research confirmed the likelihood that the introduction happened through clouds over ocean — a phenomenon of intercontinental species dispersal previously reported for bacteria and fungi, but first time for alga” said the lead author, Dr. Felix Bast who works at the Central University of Punjab.

Clouds over ocean dispersal is analogous to the intercontinental flights that we take; spores of this alga from Europe get transported to India via clouds that drift across the Arabian Sea.

But if the spores travelled across the Arabian Sea all the way to Kerala and Sri Lanka, why did the phenomenon not occur in intermediate regions like Gujarat, MP?

Answering this query, Dr. Bast noted in an email to this Correspondent: “We don't have any proof for this "clouds over ocean" hypothesis, but probability is high because this is how spores of Trentepohlia get transported. How exactly these lower stratospheric clouds got into Kerala remains unknown but aerial route from Austria to Kerala won't pass through other states like Gujarat, MP etc. It might be related to monsoon as well, as Kerala is the first state which the SW monsoon strikes together with Sri Lanka.”

On how the spores get into the clouds, Dr. Bast explains: “I would presume these spores might have got transported to the clouds by wind. We are planning to work with atmospheric scientists to sample intercontinental clouds to see what kind of organisms they transport. Metagenetic analysis of air from clouds using High Efficiency Particulate Air Filters will be the ultimate proof, for which I'll soon be applying for research grant from Ministry of Earth Sciences.” He added that this microalga is absolutely harmless, and the “blood” rainwater is perfectly potable, even for vegetarians. The present study resulted in an nternational collaborative effort involving researchers from India and Austria, supported in part by INSPIRE Faculty Award.

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