Origin of life

Mostly for my own satisfaction, in my last couple of posts I have written of what is known about the beginnings of our Universe in the 'Big Bang'; how the elements were formed in Supernova explosions of huge early stars that ejected clouds of interstellar dust called nebulae; and finally the formation of our sun and its solar system in one such nebula. At the end of that last post I promised that in this one, I would summarize what is known about how life got started on Earth. I will keep that promise but it’s going to take a couple of postings to do so.

For those who may regularly visit my site, you will have noticed that, for the first time in 2 ½ years I have missed my self-imposed Sunday morning deadline this week. The main reason was that as I researched the topic of the origin of life on Earth, I was on a very steep learning curve and on Sunday, I still had a lot to understand before I was ready to write anything on such a momentous topic. It’s been a fascinating journey and I’ve enjoyed the experience so much I didn’t want to stop until I was satisfied I had a pretty good grasp of the subject.

So picking up the saga from the last posting where we left a molten Earth to cool and to form and reform the Earth’s continents, around 4 billion years ago, most molecules were probably moving slowly enough that when they collided, they interpenetrated and reacted chemically by exchanging or sharing their surface electrons. Constant volcanic eruptions would have released huge clouds that mostly contained water vapour, and carbon dioxide [CO₂], with lesser amounts of methane [CH₄], sulfur dioxide [SO₂], nitrogen, carbon monoxide [CO], ammonia [NH₃], hydrogen sulfide [H₂S] and others; gases that contained all the main elements essential for life. 

Miller-Urey experiment 

The water vapour condensed and rained down in torrential storms that created the oceans while frequent lightening flashes helped cause the evolution of Chemistry to create ever more complex organic molecules. The experiment performed in 1953 by Miller and Urey was the first to prove that molecules of life like amino acids were formed in this manner. This important discovery inspired a multitude of further experiments that in turn produced an amazing variety of the molecules of life - like the nucleotide base, adenine for instance, which is one of the most important organic molecules for life as we know it today. Adenine is an integral part of DNA, which is found in every cell and spells out the genetic code used for directing the chemistry of cellular life. Adenine and similar nucleotide bases are found also in RNA, a smaller molecule that actually reads the DNA code and is the catalyst that performs the chemistry that it dictates.

We have known for many years that life depends on chemical reactions to exist and that life itself is a special form of chemistry in which the reactions are self-contained and self-sustaining and that they lead to their own replication and therefore growth.  So when we think of the origin of life, we see that the organic molecules involved in the chemistry of life were present; there were the abundant sources of energy available to push chemistry between them toward ever more complex interactions, and it is in the evolutionary nature of phenomena of many natural emergent events that have occurred on Earth that some form of primitive life would have evolved. By its very nature however its origins could leave us no fossil record and so we are left to speculate until life can be started, with the right conditions and compounds, in the laboratory.

This week I’ve enjoyed not feeling the constraint – self imposed though it may have been – of having to meet a deadline on Sundays so have decided to just post when I have found something new and interesting that I feel compelled to write about.  I’ll be back soon with more on what is known about the beginnings of life on our planet.  Rie  

Birth of Earth

The beautiful Eagle Nebula

In my last post I described the dying of a huge star in a spectacular supernova explosion that spewed out chemically enriched dust and gases that formed a nebula cloud out of which a solar system like ours emerge. It is because astronomers have studied new solar systems in various stages of evolution, that we now have well accepted theories about how our own developed.   

Apparently, under the force of its own gravity the portion of the nebula cloud from which we came into being, contracted over a period of around 10 million years or so and, as it shrank, material was drawn in from space around it. The increasing amount of matter resulted in a larger gravitational pull and made material speed inward ever faster. When this mass smashed into the center, its energy of motion was transformed into heat energy and the temperature increased until it reached around 15 million degrees. At that temperature, the nuclei of hydrogen atoms are moving so fast that when they collide, they fuse forming Helium nuclei and give off incredible amounts of heat and light energy. That is the story of how our sun was born in our corner of cold dark space. The marvelous process by which stars are created is more fully illustrated in a posting I did on the sun a couple of years ago.

In the process of its formation, the sun had pulled in 99.86% of the matter in its vicinity and the slight rotation of the nebula cloud had speeded up so that the remaining 0.14% of matter  formed into planets that had just enough speed that they didn’t fall into the sun but orbited around it. As the planets grew by sweeping up the all the dust and rocky debris in their orbits, the birth of the sun sent out a blast of solar wind that cleared out all the remaining dust and rubble. 

Click on picture to enlarge & read the
thickness of the layers of Earth's interior

It’s interesting to have a look at the video simulation of all of this happening.  The video also depicts the Earth  in its early years when it was a molten mass and the heavy liquefied iron-nickel alloy sank to the center. Not mentioned is that the Earth’s mantle is kept molten by radioactive elements like uranium that give off heat as they decay. The story of the cooling of our planet and how our continents formed is told in some detail in an earlier post about the ‘Earth’s Crust’. 

Earth turned out to be the only one of the eight planets in our solar system that was at just the right distance from the sun to have a temperature range suitable for life. It has been speculated for years that there are other planets like ours in the Universe but it is the recent detection of billions of new planets that sparked my interest in going back to the very beginning and writing about the spectacular events that eventually produced our planet Earth. 

It is obvious that it has been a natural process and now, with the confirmation of so many other planetary systems, the probability that other intelligent beings exist becomes more real.  The problem is, with what we know of the Laws of Physics, it would take us at least 75,000 years to just reach the closest star similar to our own. That means we’ve no place to go if we don’t smarten up and keep our beautiful planet Earth habitable. For me it also increases the importance of the SETI  [Search for Extra-Terrestrial Intelligence]   program that searches for non-natural radio signals from sections of space outside our Solar System.  

Next week, if I find enough time to research it, the subject of my post will be what we know about how life started on Earth.  Rie

                                                                        

Supernova

There are just over 100 elements in our Universe and many of them are found in each of us. I’ve been fascinated to learn over the years about how the elements were first created in the stars and then made available throughout our Galaxy so that they were accessible when we were evolving on planet Earth. I will attempt to tell that story in this post so that its marvels and violence are clearly revealed.

It’s a well-accepted scientific theory that in the beginning there was the ‘Big Bang’ when our Universe exploded into being as a condensed state of pure energy. That happened about 13.7 billion years ago and ever since it has been expanding. Evidence suggests that energy was converted into the most basic particles of matter through the relationship Einstein revealed in his famous equation: 
            E=mc²        where E stands for energy; m, for mass and 
                                c², for the enormous speed of light multiplied by itself.                                 Many thousands of years later when things cooled further, atoms, most of them of the simplest element, Hydrogen, formed from the basic particles and the stage was set for the first suns to be born.

The distribution of matter was not entirely uniform in the early Universe and giant clouds of hydrogen tended to coelesce as the force of gravity drew them together. As the mass of the accumulation increased, the gravitational force became ever stronger until the nuclei of the Hydrogen atoms were smashing into each other so fast that they fused, forming the nucleus of the next heavier element Helium that, though made of two Hydrogen nuclei, weighs a little less. That mass was converted to heat energy and the temperature increased to around 15 million degrees Celsius.  To see a simulation of this process in which a star is born, click on the video.  

The colossal stars in the early universe were 1000 times larger than our sun and when all the Hydrogen was used up and converted to Helium, the core contracted. That caused an increase in temperature and the Helium nuclei began to fuse, again giving off energy, and forming the nuclei of the element Carbon. When all the Helium is used up, shrinkage again increases the temperature and carbon nuclei fuse. In the video showing this, I love how the two guys tell the story of how each element is formed until you come to the element Iron. When iron nuclei fuse, no mass is lost and so no energy is created and the star dies and begins to collapse inward. As the core falls in on itself, it bounces off sending a wave of material outward that hits the wave of the matter collapsing from the outer layers and then a stupendous explosion occurs called a supernova that flashes in the sky with the light equivalent to that given off by 4 billion smaller stars like ours and can be seen from Earth.  In that whole energetic process, the rest of the elements are formed and spewed with tremendous momentum throughout the galaxy as stardust. We are made of that stardust!  Rie