What’s red, wet, and even apocalyptic for
some? It’s blood rain. While the rain is not actually blood, its
strange appearance has instilled fear into many who have witnessed it. In ancient times, blood rain, which is also
called red rain, was considered a bad omen. NASA Earth Observatory describes an early
account of red rain by the Roman historian Livy back in 191 BC. It disturbed the Roman Senate so much that
they “decreed that the consuls should sacrifice full-grown victims to whatever gods it deemed
proper.” Another source states that “in Germany,
showers of blood rain warned villages of the outbreak of the Black Death in 1348 – 1349.” Over the years, superstition has given way
to more rational explanations of this striking phenomenon, which we will explore, in this
episode of The Infographics Show, “What Caused The Blood Rain?” One common source of blood rain is dust from
the Sahara Desert combining with storm clouds. According to NASA Earth Observatory, “colored
rain (or snow) occurs when dust plumes and storm systems meet, though only when raindrops
fall through a dust plume beneath the level of the clouds.” How red the rain is depends on the amount
of iron oxide the dust contains. Low amounts of iron oxide will make the rain
seem more brown than red. And not all blood rain events stain everything
they touch red. It depends on the concentration of dust to
rainwater. Weather expert Philip Eden states, “’Heavier,
more prolonged rainfall simply ends up washing away the residue.’” Where the blood rain from Saharan dust falls
depends on wind and weather patterns. It often appears somewhere in Europe. The BBC reports that “’blood rains happen
a few times a year in the UK” but is “more common in southern Europe like Spain and the
South of France, which are closer to the Sahara.” A strange variation on blood rain caused by
red dust occurred in Siberia earlier this year. On July 3, 2018, blood rain fell in the industrial
town of Norilsk. A Live Science article reported that “the
plaguey rain stained cars red, spread blood-colored puddles over the asphalt and cultivated the
general vibe of a town turned into ‘a horror movie,’”. While the blood rain created excitement and
alarm for some living in Norilsk, its cause turned out to be rather mundane. Instead of red dust from the Sahara Desert,
the dust came from a local, man-made source. Live Science reports that wind blew away a
large amount of uncovered iron oxide (rust) residue from the local Nornickel metallurgical
plant. The rust dust drifted over the plant’s parking
lot, and the wind combined it with rain that was falling at the time. These conditions created a miniature blood
rainstorm that the locals will probably remember for years to come. Besides colored dust, there are also biological
causes of blood rain. Two examples of biologically-derived blood
rain occurred in recent years. One article provides an overview of an incident
that happened in 2001. It describes how the state of Kerala in India
had a series of recurring blood rainstorms: “For two full months through the end of
summer, every time it rained, the land was drenched crimson.” At first, scientists thought it might be dust
from the Rub’ al Khali desert in Saudi Arabia creating a scenario similar to the one caused
by Saharan dust in Europe. This theory was rejected after two physicists
named Godfrey Louis and Santhosh Kumar made the surprising discovery that the particles
were actually living cells. What added to the mystery was that Louis and
Kumar could not find nuclei or other genetic material in the cells. There was another strange element – reports
of a “loud bang distinct from thunder” occurring just hours before the first blood
rain. Because of these factors, they proposed that
the cells were extraterrestrial in nature. They theorized that the blood rain in Kerala
was caused by panspermia, which the article describes as “organic material moving from
one world to another.” More specifically, they believed the red “alien”
cells were from a comet that entered Earth’s atmosphere and exploded over Kerala. Most of the mass media loved the panspermia
theory and ran stories about it without questioning it. However, there is a third and more plausible
theory about the cause of Kerala’s blood rain. Scientific examination of a red rainwater
sample by Kerala’s Centre of Earth Science Studies (CESS) revealed that the “particles
appeared to be spores.” Government botanists reproduced the spores
and discovered upon re-examination that the they were “those of an unremarkable, and
extremely common, local algae called Trentepohlia,” which is “heavy with red-orange carotenoid
pigments.” The specific type of Trentepohlia is Trentepohlia
annulata. Trentepohlia spores are described as “stratospheric
spores.” This means that they are typically “found
in the atmosphere.” Instead of dust, an unusually large bloom
of spores mixed with storm clouds in the area, and blood rain was the result. The article pointed out that the main flaw
in Louis and Kumar’s research technique is that they “tried dying the spores without
growing them,” with the end result being that the “cell membranes remained intact
and they saw no genetic material.” If they had cultured the cells the way the
botanists did, they could have broken the cell walls, which would have made the cells
easier to dye and the genetic material easier to see. Louis and Kumar probably did not think of
doing this because “they were physicists and were completely outside of their specialty.” Unfortunately, despite this solid scientific
evidence about Trentepohlia spores, Louis and Kumar’s alien spores from outer space
still remain a popular explanation for Kerala’s 2001 blood rain incident even today. In 2014, a similar but less exciting blood
rain incident happened in Zamora, Spain. When blood rain fell there, a resident took
samples of the red rainwater and gave them to scientists at the University of Salamanca. University researchers examined the samples
and found that, as in Kerala, the cause of the blood rain was algae. However, it was a different type of algae
called Haematococcus pluvialis. According to one source, this freshwater algae
is green but “turns red in times of chemical stress” due to a “carotene pigment called
astaxanthin.” However, one mystery that the researchers
could not solve was where the Haematococcus pluvialis spores came from. They are not local to the area and are not
found in nearby water sources. While blood rain may be startling to see because
it seems abnormal, it is really nothing to be afraid of. In the recent examples we have seen of red
dust causing blood rain, the red dust has been sand particles from the desert and rust
scrapings from a metallurgical plant. The levels of dust involved in these blood
rain events were not dangerous to humans. In the cases of blood rain in Kerala and Zamora,
neither type of algae is harmful to humans. In a discussion of Trentepohlia spores in
a 2015 news article, Dr. Felix Bast of the Central University of Punjab said that “this
microalgae is absolutely harmless.” He also states that “‘blood’ rainwater
is perfectly potable, even for vegetarians.” As for the algae responsible for the blood
rain in Spain, it is safe enough to eat. A Daily Mail article notes that “Haematococcus
pluvialis is used in the pharmaceutical industry for its antioxidant properties and in food
production, to give salmon and trout a deeper red colour.” Have you ever seen blood rain, or have you
seen some other unusual type of rain? Let us know in the comments! Also, be sure to check out our other video
called Cannibal Island: The Real Battle Royale! Thanks for watching, and, as always, don’t
forget to like, share, and subscribe. See you next time!
