I remember sometime in 2010, my mum was concerned about a rain that was going to fall in the Lagos area of Nigeria. She had heard this from news outlets that the acid rain was going to fall and people should stay indoors. Actually, NASA later called the news false after all, and I did not eventually see the acid rain. Now you see, there are a lot of things that have fallen from the sky and you must have even heard that fishes fell with rain from the sky. Hey it isn't manna, rather it is hypothesized that strong Ocean wind such as tornadoes carry water from sea and oceans along with water creatures which fish is the most common of them. That said,in this post, I want to discuss some things that have fallen from the sky.
Back to the acid rain. The thought that acid is fallen from the sky can be scary but then a rain is regarded as acid if it has precipitation with acidic components. Actually, acid rain comes from the emission of Sulfur dioxide and Nitrogen oxide which was burnt from industries and in cars which goes into the air mixing with oxygen and water to form sulfuric acids and nitric acid which would fall as droplets.
needpix
At some point it was corrosive destroying crops in regions like China and killing marine lives in lakes in certain regions of the US and Canada. But in recent times we haven't been hearing of acid rain again, and this is because regulations and laws were made to curtail the emission of those compounds.
Talking about things that fell with rain, we can talk about the red rain that fell in the morning of July 25th, 2001 in Kerala, India. Something like a blood rain if you would call it so. The can continued sporadically for several days until 23rd September 2001. Some report said that after the rain trees shared their leaves and then turned burned gray color.
Godfrey Louis who was a physicist decided to take a look at the water under an electron microscope where he found red particles that were similar to biological cell but with no DNA. he published his result in the Journal of Astrophysics and space in 2006 where he said that he cell like particles are a kind of alternate life from space if they cells are biological or have a cometary origin. He concluded that it could be a case of cometary panspermia. He and Chandra Wickramasighe were able to discuss this for a long time and after further studies, they realized that at 121 degree celcius, the cells reproduced but remained inert at room temperature. They could not prove that the rain was from an extraterrestrial origin, they were only able to suggest.
In 2013, a paper in microbiology changed the entire course of the research when they were able to show that the cells had DNA. They continued to say that the pigment in the water was the reason for the previous failure to identify the DNA from the red rain water. Just as the research continued, another red rain happened in the villages of Zamora in Spain and when the sample was checked it contained the organism Haematococcus pluvialis which is a green alga that turns red when chemically stressed, and the pigment Astaxanthin in the alga was responsible for the coloration of the rain water. This is why it is known as the blood rain alga.
Before you start to think that it was the same algae that caused the blood rain in India, let me quickly break it to you that it is not the same. The algae responsible for the blood rain in India is known as Trentopohlia annulata. Although this alga aren't native to these countries but it is believed that its spores went through the air and precipitated after which it fell along with the rain.
Reference
https://www.vanguardngr.com/2010/03/panic-over-acid-rain-in-lagos/
https://www.bbc.com/future/article/20190823-can-lessons-from-acid-rain-help-stop-climate-change
https://www.firstpost.com/explainers/raining-fish-australian-town-lajamanu-fish-falling-from-the-skies-12198912.html
https://www.epa.gov/acidrain/what-acid-rain
https://ui.adsabs.harvard.edu/abs/2006Ap&SS.302..175L/abstract
https://www.researchgate.net/publication/1778007_The_Red_Rain_Phenomenon_of_Kerala_and_its_Possible_Extraterrestrial_Origin
https://www.discovermagazine.com/the-sciences/indias-red-rain-still-cloudy-with-a-chance-of-alien
http://www.todayifoundout.com/index.php/2017/11/casued-red-rain-kerala/
https://redrainkerala.com/reliving-the-red-rain-event-of-2001-in-kerala/
https://www.mysteryofindia.com/2014/09/mystery-of-red-rain-in-india.html#google_vignette
https://www.bbc.com/news/magazine-20028490
https://arxiv.org/pdf/astro-ph/0601022.pdf
https://arxiv.org/ftp/arxiv/papers/1008/1008.4960.pdf
https://www.hilarispublisher.com/open-access/european-species-of-subaerial-green-alga-trentepohlia-annulata-trentepohliales-ulvophyceae-caused-blood-rain-in-kerala-india-2329-9002-15-144.pdf
http://www.todayifoundout.com/index.php/2017/11/casued-red-rain-kerala/