Podcaster: Avivah Yamani
Title: Life
Organization: Astrosphere new Media
Link : http://astrosphere.org
Description: What is Life..and what kind of life that we looking for in this universe?
Bio: Avivah is a project director of 365 Days Of Astronomy and astronomy communicator from Indonesia.
Transcript:
If we look at the earth, shortly after its formation some 4,6 billion years ago, our planet was a lifeless and inhospitable place. But after we examine rocks that were created about a billion years later, we can find that 3,5 billion years ago life was already established on Earth. But have you ever asked yourself what is life? According to the Merriam Webster dictionary, Life is: the ability to grow, change, etc., that separates plants and animals from things like water or rocks; the period of time when a person is alive; and the experience of being alive.
But again… how would you define life? This is important because as we grow up and learn more we have found another question: Are we alone? This is the most basic question that has been pondered for many centuries. But how do we know and how do we recognise another life form if we can’t define life itself.
As living organisms, we consider life forms to be fundamentally different from non-living matter. However, defining life is not that simple, and many current definitions of life attempt to do so by enumerating life’s key properties but still scientists can’t yet agree on an absolute definition.
Trying to define life is not just a philosophical exercise. We need to understand what separates living creatures from non-living matter before we can claim to find life elsewhere in the Universe. Most biologists would identify two key features that indicate life: the capacity for self replication and the capacity to undergo Darwinian evolution.
For an organism to self replicate, it must be able to produce copies of itself and for darwinian evolution to occur, imperfections or mutations must occasionally arise during the copying process. And all these new mutations must be subject to natural selection.
The cell is the basic unit of all life on Earth. Complex organisms, including animals and plants, are composed of eukaryotic cells, which are characterized by having nuclei containing most of their genetic information. Simple cells, such as those of bacteria, lack nuclei and are referred to as prokaryotic.
All living organisms on Earth are composed of one or more cells. Sub-life forms that are not composed of cells, such as viruses, cannot function and reproduce on their own. Living organisms process energy and have the capability to grow and reproduce. But fire shares these same attributes. Cells and ecosystems are both able to harvest energy, metabolize, replicate and evolve; this ensemble of properties can be considered as fundamental to life. The ability of organisms to undergo Darwinian evolution is an important aspect of life on Earth. However most macroscopic organisms cannot survive independently. But defining life to be a self-sustaining system capable of undergoing Darwinian evolution has considerable merit.
For life to be sustaining and capable of Darwinian evolution both energy and minerals must be extracted from the surrounding environment to allow growth and replication. And some sort of living apparatus must be present to govern and facilitate the chemistry of life.
So what’s important for life? There is only one element that can form molecules of sufficient size to perform some of the functions necessary for life as we know it. And that element is carbon.
Carbon can form chemical bonds with many other atoms which allows a great deal of chemical versatility. Commonly organic compounds also contain elements such as hydrogen, oxygen, nitrogen, sulfur and phosphorus. Also iron, magnesium and zinc can be bond with carbon.
It also can form compounds that readily dissolve in liquid water which also is very essential for life on earth. And the fundamental elements which develop into living organisms on Earth must be able to interact readily with one another, and that occurs most readily in the presence of water.
The life we know now utilizes carbon-based organic compounds and the universe is well stocked with the elements needed to construct it.
The other essential component for life is liquid water. Living systems need a medium in which molecules can dissolve and chemical reactions can take place. And water is the answer since it performs these functions so well. Liquid water exists in a warm temperature which is not too cold to sustain biochemical reactions and not too hot to stop many organic bonds from forming. As an alternative, ammonia would be liquid on a world much colder than Earth. And in such low temperatures, chemical reactions that could lead to life would operate sluggishly and living systems may struggle to establish.
So how did life arise on earth?
Evidence suggests that life evolved for the first time around 3.5 billion years ago. It took the form of microfossils and ancient rock structures in South Africa and Australia called stromatolites which were produced by microbes that form thin microbial films which trap mud. Over time, layers of these mud/microbial mats can build up into a layered rock structure. This stromatolites still exist now and have similarity with the ancient one.
One hypothesis says life originated near deep sea hydrothermal vents. The chemicals found in these vents and the energy they provide could have fueled many of the chemical reactions necessary for the evolution of life. Even though the evidence is consistent with the hypothesis that life began near deep sea vents, it is far from certain: the investigation continues and may eventually point towards a different site for the origin of life.
To find another life in the universe in terms of life as we know it, we need to find the most essential component for life itself. One of the main ingredients for life as we know it is liquid water. That’s why astronomers are looking for another world that could support liquid water on its surface. Water exists as a liquid between 273K and 373K. And to find that kind of planet, it should be something like earth, a terrestrial planet in the star’s habitable zone, the region around a star that’s not too hot or too cold for a planet to support liquid water on its surface.
The life we are looking for is not only human-like or complex like plants or animals. But life could be as simple as bacteria. Millions of years ago Earth was only able to sustain microbial life, today it can also maintain plants and animals and supports a more diverse biosphere.
Aside from being in the star’s habitable zone, the planet should have similarity with Earth and hold an atmosphere with basic ingredients for life, such as carbon dioxide, oxygen, nitrogen, water vapour, ammonia, and methane in certain amounts.
From all the extrasolar planets we have found up to now, there are only 21 that can be considered habitable planets. We haven’t found what we are looking for yet, but that doesn’t mean there is no other life out there. But is it life as we know it or will it be another kind of life that we have never known before?
365 Days of Astronomy is a community podcast made possible thanks to the contributions of people like you. Please consider donating at 365DaysofAstronomy.org/Donate
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Reference:
Conway. A., I. Gilmour, B.W. Jones, D.A.Rothery, M.A. Septhon, J.C. Zarnecki. 2003. An Introduction to Astrobiology. Eds: I. Gilmour & M.A. Sephton. Cambridge University Press
Lissaeur, J.J., Imke de Pater. 2013. Fundamental Planetary Science. Cambridge University Press
From Soup to Cells—the Origin of Life
End of podcast:
365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by Astrosphere New Media. Audio post-production by Richard Drumm. Bandwidth donated by libsyn.com and wizzard media. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. In the new year the 365 Days of Astronomy project will be something different than before….Until then…goodbye