Earth's early atmosphere - question
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Earth's early atmosphere - question
Post #1The Miller-Urey experiment and other similar experiments are based on our knowledge of Earth’s early atmosphere. They usually involve some combination of water, methane, ammonia, hydrogen, and carbon dioxide. But how do we know (or why did we think) that these chemicals would have made up the atmosphere so many billions of years ago? How did we reach that conclusion, and how certain are we?
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Neatras
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Post #2
There are a number of methods we could use. Comparison with other planets, the elemental composition of Earth, the calculations based on half-lives of radioactive matter and what the abundance of certain elements would mean in terms of molecular composition for atmospheric conditions. Additionally, by understanding that such an environment would be prebiotic, it becomes trivial to recognize that many of the molecules that living organisms regularly circulate through the atmosphere would not naturally be present. As you'll find in any and all scientific articles from the last 20 years, the early atmosphere contained trace amounts of oxygen.
We can also find evidence of atmospheric composition using ice cores, which are very reliable records for what the environmental conditions were during each year as layers were added; different compositions of gases would cause different structures , thickness, and layer compositions to form.
To review: We can make predictions about early earth's history based on what we know about molecular chemistry. For example, by taking into account the different ways in which hydrogen, carbon, oxygen, and nitrogen bond with each other and are added/removed from the atmosphere, we can speculate that the early atmosphere contained large amounts of CO2 and N2 as opposed to CH4 and NH3.
We can make predictions about early earth's history based on what we know about ice cores. For example, if the planet's average climate is warmer one year than the next, then the ice layer will correspond to that. The cyclical nature of melting and freezing doesn't erase all data; it removes the permafrost and provides a kind of canvas for future ice to form that will carry characteristics of carbon content in the air, local temperature, and compare the quantity of greenhouse gases across a long time-scale.
We can make predictions about early earth's history based on what we know about biology. Because the oxygenated atmosphere was not present up until a certain point in history (according to geological evidence), any life did not rely on oxygen to sustain itself. Due to the plasticity and adaptability of life, however, when oxygen became prevalent, most of our living precursors gradually filled in the niche so as to take advantage of the oxygen-rich atmosphere. Photosynthesis would eventually create a stable cycle, and this can be corroborated by looking at the evidence for photosynthetic microbial organisms and the early ancestors of plants.
Modern-day creationists shoot themselves in the foot by trying to divorce historical science from classical physics and chemistry. According to them, eyewitness testimony is the only way to confirm events. Setting aside the hypocrisy of Christendom et al making countless unverified claims about the past, we can still take note that this position isn't based on any kind of realistic or pragmatic approach to nature. Due to the consistency of universal physics and chemistry, we can assume that the conditions that give rise to a physical phenomena are understandable, and finding evidence that physical phenomena occurred in the past is direct evidence of those conditions. Forensic science is the tongue-in-cheek response to folks like Ken Ham who obfuscate and misrepresent science so as to try and put his bronze age mythology beyond the "purview of science" (as the terminology is put across by modern creationists parroting the limited think tank of liars and conmen who come up with these backwards, anti-intellectual arguments).
Yes, our calculations and predictions are all based on approximations, and they all rely on making the most out of all physical data available at the time of hypothesizing. We also acknowledge that future data will correct discrepancies and get us closer to a realistic answer. This is what science is supposed to do. Creationists see the above two sentences and declare, "Aha! If everything you know about science will be overturned in 100 years, why bother pretending you can make predictions?" This anti-intellectual approach is actually a poisonous element that would put us back in the Stone Age if we gave it any credibility. Fortunately, we don't have to. Because while our estimations are incomplete, they are also mindful of their incompleteness. Error bounds that account for missing physical data continually become refined and move us toward a more precise answer. Early theories are not some be-all, end-all declaration of exact physical conditions. They are always approximations based on available evidence, and a good theory will give a window for new discoveries to tell a theory whether they are moving toward one end of the error bound or the other. But, surprise surprise, lots of good theories end up remaining within the range of predicted values, with new data and variables often shrinking the error bound to a more precise range. Because science operates under the assumption that limited data means approximation, and more data means precision.
And the statement that scientific theories get thrown out every 100 years is still a load of malarkey. I leave it as an exercise to Creationists to please try and mull it over for a good hour and come up with reasons why it is such a backwards position to take; I assure you, if you apply critical thinking to that kind of statement, you will see flaws and realize the error.
Lastly, eyewitness testimony isn't admissible in court, and for good reason. Experiential evidence is inherently flawed due to the poor memory capabilities of humans. Measuring instruments, repeated experimentation, and an objective understanding of reality based on a reliance on accumulation of knowledge is what leads to impartiality and gives scientists the credibility to do their work; it is not something a layman can understand or dismiss at a glance.
We can also find evidence of atmospheric composition using ice cores, which are very reliable records for what the environmental conditions were during each year as layers were added; different compositions of gases would cause different structures , thickness, and layer compositions to form.
To review: We can make predictions about early earth's history based on what we know about molecular chemistry. For example, by taking into account the different ways in which hydrogen, carbon, oxygen, and nitrogen bond with each other and are added/removed from the atmosphere, we can speculate that the early atmosphere contained large amounts of CO2 and N2 as opposed to CH4 and NH3.
We can make predictions about early earth's history based on what we know about ice cores. For example, if the planet's average climate is warmer one year than the next, then the ice layer will correspond to that. The cyclical nature of melting and freezing doesn't erase all data; it removes the permafrost and provides a kind of canvas for future ice to form that will carry characteristics of carbon content in the air, local temperature, and compare the quantity of greenhouse gases across a long time-scale.
We can make predictions about early earth's history based on what we know about biology. Because the oxygenated atmosphere was not present up until a certain point in history (according to geological evidence), any life did not rely on oxygen to sustain itself. Due to the plasticity and adaptability of life, however, when oxygen became prevalent, most of our living precursors gradually filled in the niche so as to take advantage of the oxygen-rich atmosphere. Photosynthesis would eventually create a stable cycle, and this can be corroborated by looking at the evidence for photosynthetic microbial organisms and the early ancestors of plants.
Modern-day creationists shoot themselves in the foot by trying to divorce historical science from classical physics and chemistry. According to them, eyewitness testimony is the only way to confirm events. Setting aside the hypocrisy of Christendom et al making countless unverified claims about the past, we can still take note that this position isn't based on any kind of realistic or pragmatic approach to nature. Due to the consistency of universal physics and chemistry, we can assume that the conditions that give rise to a physical phenomena are understandable, and finding evidence that physical phenomena occurred in the past is direct evidence of those conditions. Forensic science is the tongue-in-cheek response to folks like Ken Ham who obfuscate and misrepresent science so as to try and put his bronze age mythology beyond the "purview of science" (as the terminology is put across by modern creationists parroting the limited think tank of liars and conmen who come up with these backwards, anti-intellectual arguments).
Yes, our calculations and predictions are all based on approximations, and they all rely on making the most out of all physical data available at the time of hypothesizing. We also acknowledge that future data will correct discrepancies and get us closer to a realistic answer. This is what science is supposed to do. Creationists see the above two sentences and declare, "Aha! If everything you know about science will be overturned in 100 years, why bother pretending you can make predictions?" This anti-intellectual approach is actually a poisonous element that would put us back in the Stone Age if we gave it any credibility. Fortunately, we don't have to. Because while our estimations are incomplete, they are also mindful of their incompleteness. Error bounds that account for missing physical data continually become refined and move us toward a more precise answer. Early theories are not some be-all, end-all declaration of exact physical conditions. They are always approximations based on available evidence, and a good theory will give a window for new discoveries to tell a theory whether they are moving toward one end of the error bound or the other. But, surprise surprise, lots of good theories end up remaining within the range of predicted values, with new data and variables often shrinking the error bound to a more precise range. Because science operates under the assumption that limited data means approximation, and more data means precision.
And the statement that scientific theories get thrown out every 100 years is still a load of malarkey. I leave it as an exercise to Creationists to please try and mull it over for a good hour and come up with reasons why it is such a backwards position to take; I assure you, if you apply critical thinking to that kind of statement, you will see flaws and realize the error.
Lastly, eyewitness testimony isn't admissible in court, and for good reason. Experiential evidence is inherently flawed due to the poor memory capabilities of humans. Measuring instruments, repeated experimentation, and an objective understanding of reality based on a reliance on accumulation of knowledge is what leads to impartiality and gives scientists the credibility to do their work; it is not something a layman can understand or dismiss at a glance.
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Neatras
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Post #4
[Replying to post 3 by H.sapiens]
Good grief, I can't believe I went off on a train of thought and made a statement like that. It's counted as less reliable than forensic evidence. It shouldn't be the sole case for conviction. Can't edit it, unfortunately. But the statement is clear: Eyewitness testimony will never amount to the same kind of standing or persuasive power as physical evidence and forensic science.
Good grief, I can't believe I went off on a train of thought and made a statement like that. It's counted as less reliable than forensic evidence. It shouldn't be the sole case for conviction. Can't edit it, unfortunately. But the statement is clear: Eyewitness testimony will never amount to the same kind of standing or persuasive power as physical evidence and forensic science.
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DrNoGods
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Re: Earth's early atmosphere - question
Post #5[Replying to post 1 by Rufus21]
As Neatras indicated there are lots of studies on this issue, as I expect you have already discovered from web search. But if you have more interest this article published in 2010 is chock full of references both in the text and in the right sidebar (and one of the authors is an acquaintance of mine):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944365/
But how do we know (or why did we think) that these chemicals would have made up the atmosphere so many billions of years ago? How did we reach that conclusion, and how certain are we?
As Neatras indicated there are lots of studies on this issue, as I expect you have already discovered from web search. But if you have more interest this article published in 2010 is chock full of references both in the text and in the right sidebar (and one of the authors is an acquaintance of mine):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944365/
In human affairs the sources of success are ever to be found in the fountains of quick resolve and swift stroke; and it seems to be a law, inflexible and inexorable, that he who will not risk cannot win.
John Paul Jones, 1779
The man who does not read has no advantage over the man who cannot read.
Mark Twain
John Paul Jones, 1779
The man who does not read has no advantage over the man who cannot read.
Mark Twain
