The Cosmic Origins of Life

Here’s one to confound the creationist crowd: life may have begun as a result of organic molecules resulting from impacts by comets or meteorites. No supernatural foundation, no invisible hand guiding the process. Just random crashes, a little physics, some chemistry, a while lot of time, and voila: life.

But wait, there’s more…

How did these molecules go from static organic molecules to self-reproducing you ask? Ah, therein lies another tale… that of enzymes, the little engines of life. More randomness, more chemistry. No intelligent design.

Let’s start with the comets.

According to a recent article in Science Daily,

Scientists … from Imperial College London, the University of Kent and Lawrence Livermore National Laboratory discovered that when icy comets collide into a planet, amino acids can be produced. These essential building blocks are also produced if a rocky meteorite crashes into a planet with an icy surface.

The researchers suggest that this process provides another piece to the puzzle of how life was kick-started on Earth, after a period of time between 4.5 and 3.8 billion years ago when the planet had been bombarded by comets and meteorites.

The intrepid researchers fired projectiles at comet-like speeds into icy surfaces similar to what we know comets are made from.  They discovered that the shock wave slams simple molecules together into more complex forms. The heat from the impact  then transforms these more complex molecules into amino acids such as glycine and D-and L-alanine.

Dr Mark Price, co-author from the University of Kent, adds: “This process demonstrates a very simple mechanism whereby we can go from a mix of simple molecules, such as water and carbon-dioxide ice, to a more complicated molecule, such as an amino acid. This is the first step towards life. The next step is to work out how to go from an amino acid to even more complex molecules such as proteins.”

In a similar experiment, published in July,2013, scientists simulated an icy comet-like snowball using carbon dioxide, ammonia, methane, ethane and propane. They zapped it with high-energy electrons to “simulate the cosmic rays in space” and discovered that the result was “complex, organic compounds, specifically dipeptides, essential to life.”

Chemists from the University of California, Berkeley, and the University of Hawaii, Manoa, showed that conditions in space are capable of creating complex dipeptides – linked pairs of amino acids – that are essential building blocks shared by all living things. The discovery opens the door to the possibility that these molecules were brought to Earth aboard a comet or possibly meteorites, catalyzing the formation of proteins (polypeptides), enzymes and even more complex molecules, such as sugars, that are necessary for life.

So we know that impacts can create complex organic molecules, and that comets themselves may carry them. And we know comets and meteorites struck the young earth during its early history (and may have done as recently as 1908  – some may have caused geologically recent climactic changes). Either the impact or the debris may have contributed to the early organic molecules on earth.

More information about the composition of comets will be discovered in 2014 when Rosetta lands a probe on  comet 67P/Churyumov–Gerasimenko. Fascinating stuff.

This notion of life from space, by the way, isn’t entirely new. A similar notion (but not founded on empirical data) called Panspermia has been around since the 19th century. Back int he 1970s, astronomers Sir Fred Hoyle and Chandra Wickramasinghe hypothesized that space dust was mostly organic and that some hardy life forms (extremophiles) might have survived the journey across interplanetary and even interstellar space to land on Earth and thrive here.*

While this notion has not had a lot of scientific support, there is more interest in pseudo-panspermia:

Pseudo-panspermia (sometimes called “soft panspermia” or “molecular panspermia”) argues that the pre-biotic organic building blocks of life originated in space and were incorporated in the solar nebula from which the planets condensed and were further —and continuously— distributed to planetary surfaces where life then emerged.

In a related story on Science Digest,  UNC School of Medicine biochemist Charles Carter’s team,

… recreated ancient protein enzymes that likely played a vital role in helping create life on Earth. Carter’s finding flies in the face of the widely-held theory that Ribonucleic Acid (RNA) self-replicated without the aid of simple proteins and eventually led to life as we know it.

Carter’s group recreated ancient protein enzymes in the lab and the results suggest they  played a vital role in creating life. However, this challenges a long-held belief that life formed from self-replicating Ribonucleic Acid (RNA). Some scientists have argued this is unlikely because they,

…calculate that it would take much longer than the age of the universe for randomly generated RNA molecules to evolve sufficiently to achieve the modern level of sophistication. Given Earth’s age of 4.5 billion years, living systems run entirely by RNA could not have reproduced and evolved either fast or accurately enough to give rise to the vast biological complexity on Earth today.

Carter, instead,  superimposed digital three-dimensional models of modern enzymes in our genetic code and found they had, “virtually identical cores.” His team extracted these cores as “molecular fossils” Carter named “Urzymes.”

Both Urzymes are very good at accelerating the two reactions necessary to translate the genetic code.
“Our results suggest that there were very active protein enzymes very early in the generation of life, before there were organisms,” Carter said. “And those enzymes were very much like the Urzymes we’ve made.”
The finding also suggests that Urzymes evolved from even simpler ancestors — tiny proteins called peptides. And over time those peptides co-evolved with RNA to give rise to more complex life forms.

Peptides, working with RNA might be one of the key kickstarters to self-replicating life. Carter is “extending his research to include polymerases — enzymes that actually assemble the RNA molecule” to see if they also played a part.

Pretty exciting stuff.

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* The discovery of the Pandoravirus in July, the largest virus yet discovered, may yet revitalize the life-from-space-extremophile theory. According to The Daily Mail,

When the team studied them they found that their genetic code was twice the size of the Megavirus, which was previously the biggest virus ever found at around 440nm.
However, they were in for more of a shock as only six per cent of its genes resembled genes seen before in other organisms on Earth.
Dr Claverie told NPR: ‘We believe that those new Pandoraviruses have emerged from a new ancestral cellular type that no longer exists.’
He went on to explain that it is possible that they have come from another planet, such as Mars.

Don’t get too excited (too late… the wingnuts already leapt on it.). The doctor also noted rather more prosaically that,

Alternatively, its unusual genome could have developed as a result of it picking up genetic material from its hosts.

And in a more reserved manner, Nature commented:

They do, however, contain some of the core genes that are common to giant viruses, and they have a viral life cycle. Under an electron microscope, the researchers saw the viruses being taken up by amoeba hosts, emptying their proteins and DNA into the host cells, commandeering the host-cell nuclei, producing hundreds of new viral particles and, finally, splitting the host cells open.

The researchers are now trying to determine the viruses’ origins by characterizing the unknown genes and the proteins they encode. They have long suspected that giant viruses evolved from cells; if they are right, the ancestors of Pandoraviruses must have been very different from the bacteria, archaea and eukaryotes we have today. “We think that at some point, the dynasty on Earth was much bigger than those three domains,” says Abergel. Some cells gave rise to modern life, and others survived by parasitizing them and evolving into viruses.

So no Martian viruses, sorry. Simply because they challenge some ideas about viruses doesn’t mean they’re not from here.