Molecules, Light And Life: Fill & Download for Free

Is it possible that life elsewhere might not be carbon-based? Certainly. But it is more likely that it is carbon-based. Why? Chemistry.I've highlighted a column in the periodic table, with a red border. Carbon is at the top of this column. Carbon is the lightest, most abundant, element with four valence electrons in a shell capable of eight. That means a carbon atom can form four covalent bonds while nitrogen (to its right) can form three and oxygen (to nitrogen's right) can form two. Here is a diagram of methane, an example of carbon using all four bonds.Carbon can also form double bonds, allowing strong (but not so strong the molecules can't change), complex, branching molecules, like this butene molecule.This means carbon is a light and abundant element capable of forming very complex and flexible molecules. Life is complex. Life needs to be flexible to survive.But what about the other elements in the red box? Well, there is something called the double bond rule that says period 3 and below do not readily form double bonds. If they do, the bonds are weak. So, the lower we go down that column the less likely life can form based on that element. Silicon can form double bonds with itself, forming diselenes which are unstable. Silicon is a possibility for life, but far less likely than carbon. Science fiction authors like to use it, such as in the Star Trek episode, Devil in the Dark, where the crew of the Enterprise met the silicon-based Horta.So, the primary reason we look for carbon-based life is that it is more likely to exist. But the secondary reason is that we know what it looks like. There might be other life out there that is not carbon-based, but it might be so foreign to us that we wouldn't recognize it as life.

Is it possible that life elsewhere might not be carbon-based? Certainly. But it is more likely that it is carbon-based. Why? Chemistry.I've highlighted a column in the periodic table, with a red border. Carbon is at the top of this column. Carbon is the lightest, most abundant, element with four valence electrons in a shell capable of eight. That means a carbon atom can form four covalent bonds while nitrogen (to its right) can form three and oxygen (to nitrogen's right) can form two. Here is a diagram of methane, an example of carbon using all four bonds.Carbon can also form double bonds, allowing strong (but not so strong the molecules can't change), complex, branching molecules, like this butene molecule.This means carbon is a light and abundant element capable of forming very complex and flexible molecules. Life is complex. Life needs to be flexible to survive.But what about the other elements in the red box? Well, there is something called the double bond rule that says period 3 and below do not readily form double bonds. If they do, the bonds are weak. So, the lower we go down that column the less likely life can form based on that element. Silicon can form double bonds with itself, forming diselenes which are unstable. Silicon is a possibility for life, but far less likely than carbon. Science fiction authors like to use it, such as in the Star Trek episode, Devil in the Dark, where the crew of the Enterprise met the silicon-based Horta.So, the primary reason we look for carbon-based life is that it is more likely to exist. But the secondary reason is that we know what it looks like. There might be other life out there that is not carbon-based, but it might be so foreign to us that we wouldn't recognize it as life.

I am not aware of any evidence of life on other planets. I think there is, however, starting to be more and more evidence that the conditions to support life have existed and maybe do still exist, at locations other than Earth.The entire subject is challenging because we have to start by defining a term on which we have a very narrow perspective. What is Life? If life is something that can reproduce, is a mule alive? If life is something that can grow, is a crystal alive? And if we come to a consensus on what makes something “life”, does that mean all objects with those characteristics will be recognizably similar to each other?All we really know about life is based upon observations of the life that formed on the planet Earth. From those observations, we conclude that life involves carbon and life requires water. So, we extrapolate that if we can find places where water and complex carbon based molecules exist, then life may also exist. That may well be short-sighted. There may be life that doesn’t need water nor carbon.But, chemistry tells us that life is more likely to be based on carbon than on any other element. Carbon is the lightest, most abundant, element with four valence electrons in a shell capable of eight. That means a carbon atom can form four covalent bonds while nitrogen (to its right) can form three and oxygen (to nitrogen's right) can form two. Carbon can also form double bonds, allowing strong (but not so strong the molecules can't change), complex, branching molecules. This means carbon is a light and abundant element capable of forming very complex and flexible molecules. Life is complex. Life needs to be flexible to survive.Water is also viewed as a near prerequisite for life. Water is a universal solvent. It can dissolve many substances, making it extremely valuable at transporting materials in and out of living cells.So, we look for complex carbon molecules and we look for water and we look for temperatures at which that water can be a fluid.Just three months ago, NASA announced that flowing water had been observed on Mars. Researchers studying imagery from the Mars Reconnaissance Orbiter observed grooves formed by the transport of salts via water.Four months before that, other researchers published a paper on late-stage formation of Martian chloride salts that posited that in the area they studied, a lake existed on Mars 3.6 billion years ago. At that same time, the Archaen eon, it is believed that prokaryotes were evolving on Earth.And four months before that, another group of researchers published a paper that, based on studying atmospheric water of Mars and deuterated forms, concluded that early in its life (around 4 billion years ago) Mars had a global equivalent water layer at least 137 meters deep.If Mars had liquid water for hundreds of millions of years, it could certainly be possible that life, if even just for a geologically brief period, did appear on Mars.NASA missions like Cassini and Dawn are doing more than just sending us amazing images of the bodies in our solar system. They are providing data that indicates how prevalent water is in the solar system. It is believed that both Ganymede and Callisto (moons of Jupiter) and Enceladus, Titan, and Mimas (moons of Saturn) have underground saltwater oceans. Neptune’s moon Triton might also have a subsurface ocean. Just a few months ago, New Horizons sent back images showing frozen water on Pluto.In September, a paper was published in the journal Icarus, about shock experiments done to examine the potential role that cometary impacts may have played in the evolution of life. Not only could comets have provided much of the water on the terrestrial planets, but the paper suggests that comet impacts played a role in chemical evolution via supplying linear peptides.The search for exoplanets is also revealing evidence that Earth is not so unique. So far, more than thirty potentially habitable exoplanets have been found in other solar systems.There's a lot of optimism. Recently, NASA chief scientist, Dr. Stofan said:"I think we're going to have strong indications of life beyond Earth within a decade, um and I think we're going to have definitive evidence within 20 to 30 years. We know where to look, we know how to look, in most cases we have the technology, and we are on the path to implement it."