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Arsenic and Aliens

Arsenic anyone?

What do you first think about when someone mentions arsenic? Poison? Am I right?


For hundreds of years arsenic has been the favoured choice of the assassin. The 16th century Italian Borgia dynasty used it with great effect to polish off many of their rivals. It is even rumoured that Napoleon was finally nobbled with arsenic in his wine. There were certainly traces of it found in samples of his hair.

Why is arsenic such a good poison?

If you look at the periodic table Arsenic is in the same group and right next door to Phosphorous. Phosphorous happens to happens to be one of the six essential elements needed for life. (The other five being Carbon, Hydrogen, Oxygen, Nitrogen and Sulphur)

No form of life has ever been discovered that does not contain these key ingredients. They are needed to make DNA, RNA, proteins and enzymes that make all of life work.

Borgian Dynasty

Why is arsenic lethal then?


What arsenic does is fool the body into thinking it is phosphorous because it is chemically similar in many ways. The only problem is it can't actually do the chemistry needed for life. The body thinks the arsenic is the phosphorous, takes it in and tries to use it for life process, but it can't! The biochemistry just doesn't work with arsenic and the organism dies. This is the what makes any poison a poison. It has be similar to something the body needs, so that it takes it in, but different enough so that it cannot use it when it is there. Arsenic is really good at this trick.

Arsenic - the master of disguise!

Arsenic is a very abundant substance, the 20th most common element in the Earth's crust. Some places have lots of arsenic present in the environment naturally. One of these places is Mono Lake in California.

Lake Mono

This is very old lake that has been around for at least 700,000 years, and it has a very high concentration of Arsenic. Just looking at the pictures gives you a clue as to how toxic the environment is. There is not much life here; but there is some. Extremophile bacteria that can tolerate high levels of arsenic have been known to live in the lake for thirty years. Interesting beasties!

Extremely weird results!

An experiment has just been recently done to find out just how much arsenic they can survive. Most of the results were as expected. As the arsenic levels are increased the extremophiles die off one by one.


Except for a few that went “whoopee!”, had a party and started to thrive and multiply. Now this was not expected and was initially completely impossible to explain. It is difficult to stress how odd this result was. These levels of arsenic should have killed absolutely everything, according to all our knowledge of biochemistry, this was simply impossible. It made no sense at all.

What was going on? The answer sounds like science fiction. What we appear to have is a completely new form of life based on different biochemistry. It seems that these organisms are actually using arsenic instead of phosphorous in its structure. This means that it must have a different kind of DNA to every other form of life ever discovered on the Earth. This really could be important.

Where did it come from?

There are two possibilities, both very significant:

It could represent a very deep root of the tree of life. It could show a branch that started billions of years ago and has survived and evolved parallel to all the life we have known about up until now.


It could have come from somewhere else. That is it could have arrived from space at some point in the distant past and actually evolved on a different planet. We may actually have real live aliens living amongst us. This is a fairly startling thought but may actually turn out to be true.

Whichever origin turns out to be true, this is a very important discovery and shows that life can exist in ways that have never been dreamt of. It also makes the possibility of life elsewhere in the universe or even the solar system much more plausible. It seems that life may always find a way, in fact many ways to get a foothold.

Big Questions

What is the chemical recipe for life?

How do poisons work?