Arsenic’s atomic number is 33 and Phosphorus’ is 15. They share the same column in periodic table which means their chemical composition is similar.
NASA found that bacteria which is very adaptable when deprived of Phosphorus in an Arsenic rich environment, adopted to replace P with AS. Considering they both have similar chemical composition and bonding properties, is this surprising? I don’t think so. However, it is good that NASA is able to expand their definition of what life is. (note that there have been questions raised on the validity that it’s indeed life since some are asking for proof that the arsenic molecules are functional within the organism).
It’s well-known that Arsenic is poisonous to living beings. Why? Here is an excerpt from Wikipedia article on Arsenic: One of the cellular poisoning caused by Arsenic – Tissue culture studies have shown that arsenic blocks both IKr and Iks channels and, at the same time, activates IK-ATP channels. Arsenic also disrupts ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits pyruvate dehydrogenase and by competing with phosphate it uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration, and ATP synthesis. It also produces higher levels of Hydrogen peroxide. It triggers apoptosis because the cellular structure is changed.
The surprise is that NASA scientists have been searching for live in the universe and assume that it will be exactly made of same chemical bonds as we are familiar or know it.
The universe is more complex and is very difficult to understand since what we have at our disposal is just the five senses and a whole lot of imagination.
It’s assumed that water is essential component for “life”. The “life” in quotes here is very narrow definition.
Life should be defined more broadly. It should exhibit the following characteristics:
- Reproduce – This can be sexual reproduction (fusion) or asexual reproduction (fission)
- Grow – Necessary for reproduction so that the population can grow.
- Death – As important as Reproduction and growth since population explosion will starve them of nutrients without death. In a way, death is quintessential to life.
- Interact with the environment
- Being able to take chemicals from environment and convert them to energy or other useful forms is necessary for growth and reproduction
- Adopt to environmental changes – Mutation is the key for survival (though not essential for life to exist) as environment changes.
The rest of the properties we see composition using cells, organization, use of energy etc. which are described as characteristics of life.
It’s a fair assumption that life requires organic compounds those that can form covalent bonds. Ionic bonds are too strong to exhibit the characteristics. However, ionic bonds can disrupt organic compounds. Weak bonds are easy to break and as such they can easily interact with the environment, grow, divide or multiply etc.
Are there other forms of life that are in front of our eyes but we are not able to see? Stars and Galaxies – New stars are born, grow and die. Stars and galaxies collide to form new stars and galaxies. Galactic clouds are birth place of stars. They do interact with surrounding environment.
Forests – Mayan ruins were quickly engulfed by forest. There were famines and lack of water but once humans abandoned their places, forest was born, grew.
There are various other examples, ecosystems on earth, traffic in busy intersections, whole species (this is an interesting thing that life can emerge out of lower forms of life), stock market etc. that exhibit some or all of the attributes of life.
It’s great that NASA is spending a lot of effort in searching for life elsewhere but they should probably expand their definition of life. They will have better chance of finding it out there or even here on earth just like they did in this announcement.