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T. McGrath

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  1. The original 1998 paper that paved the way for the existence of Dark Energy set out to calculate how quickly the universe was slowing down. They were not expecting the results that they got. Using 30 Type Ia SNe observed at z = 0.5 and 10 Type Ia SNe observed at z = 1.0 they erroneously assumed all Type Ia SNe had the exact same absolute magnitude of -19.46. We have since discovered not only a whole new class of very dim Type Ia SNe (known as Type Iax SNe) that range between -14.2 and -18.9 absolute magnitude, but also superluminous Type Ia SNe with absolute magnitudes exceeding -20. The "Standard Candle" they thought they had in the 1990s proved to be not so standard after all. At the very least it brings into question the SNe data that was used to calculate the age and acceleration of the universe. Edwin Hubble made the exact same mistake in 1927 when he used Cepheid variables as his "Standard Candle" and erroneously calculated that the universe was only ~2 billion years old. Just as a side note: I find it rather difficult to comprehend why people have no problem accepting the fact that we have confirmed the existence of exoplanets based upon the gravitational effects the exoplanet has on its parent star (without ever seeing the actual exoplanet), but they have difficulty accepting the existence of Dark Matter even when it is those very same gravitational effects that tell us something must exist. Very odd. Sources: The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Curvature of the Universe Using Type Ia Supernovae - The Astrophysical Journal, Volume 507, Number 1, 1998 (free preprint) Type Iax Supernovae: A New Class of Stellar Explosion - The Astrophysical Journal, Volume 767, Number 1, March 2013 Analytical Expressions for Light Curves of Ordinary & Superluminous Type Ia Supernovae - The Astrophysical Journal, Volume 809, Number 1, 2015 Hydrogen-Poor Superluminous Stellar Explosions - Nature 474, 487-489, June 2011 (free preprint)
  2. The interactive model can be found at: Action Dynamics of the Local Supercluster Interactive Model Source: Action Dynamics of the Local Supercluster - The Astrophysical Journal, Volume 850, Number 2, December 2017 (free preprint)
  3. Since the Sloan Digital Sky Survey began in 2014 and is on-going and will not be completed until the year 2020, good luck with that.
  4. Dark Energy also has absolutely no bearing on the original question. It is currently believed that the very first galaxies formed just prior to reionization some 400,000 years after the Big Bang. It is suggested that the active galactic nuclei (a.k.a. quasars/blazars) from what is widely believed to be elliptical galaxies that caused this reionization. However, it has also been suggested that the shape of a galaxy is determined by its rotation, and that is where Dark Matter does play a role. Elliptical galaxies having a relatively slow or no rotation, while the spiral types have a much greater rate of rotation. In such a case, the age of the galaxy would not necessarily determine whether it is elliptical or spiral, but rather the rate of its rotation. Thus, it could be possible for spiral galaxies to exist at redshifts z > 6. Sources: Early Reionization by the First Galaxies - Monthly Notices of the Royal Astronomical Society, Volume 344, Issue 1, 1 September 2003 Early star-forming galaxies and the reionization of the Universe - Nature 468, 49-55, November 2010 (free preprint)
  5. My claim actually comes from the paper that originally created the Type Iax supernova category in March 2013. Source: Type Iax Supernovae: A New Class of Stellar Explosion - The Astronomical Journal, Volume 767, Number 1, March 25, 2013 If between 18% and 48% of all the Type Ia SNe prior to March 2013 should have been classified as the much dimmer Type Iax SNe, then the age of the universe, the acceleration of the universe, and the existence of Dark Energy need to be re-examined. However, it has absolutely nothing to do with Dark Matter. Dark matter exists independently from supernovae data. Nor are supernovae used to determine the existence of Dark Matter. We are able to directly observe the gravitational effects Dark Matter has on galaxies and light. However, we cannot say the same thing about Dark Energy. Dark Energy only exists because of the questionable supernovae data collected during the 1990s.
  6. The location of the 1954 supernova appears to be coincidental. Based upon the spectrum of the 1954 supernova in NGC 4214, it was not the same star that produced iPTF14hls. The iPTF14hls supernova was rich in hydrogen, and the 1954 supernova lacked hydrogen in its spectra and was dominated primarily by helium. They were not entirely sure how to classify the 1954 supernova, but they were leaning towards a type I supernova, and iPTF14hls is classified as a Type II-P supernova. The 1954 supernova lasted between 45 and 50 days after peak brightness. It was also suggested that the progenitor may have been an OB-type star, except that it lacked the hydrogen lines and has abundant helium in its spectra. As far as ideas are concerned, could iPTF14hls be a Thorne–Żytkow object? I know that when a neutron star siphons material from a companion it becomes an X-ray pulsar (Be X-ray binary) during that period, but what if the neutron star periodically shed this outer layer of material from its companion in a similar manner as a white dwarf that has exceeded the Chandrasekhar limit? Normally there is nothing left of the white dwarf after a Type Ia supernova, but would that process also apply to a neutron star?
  7. Think of the speed of light as the current maximum speed limit for anything with mass. That does not mean that all photons are traveling at light speed, only that anything with mass cannot travel faster than light speed. If photons have to pass through a medium other than a vacuum then you can expect that they will not be traveling at their maximum speed. At Harvard University they conducted an experiment using a Bose--Einstein condensate as the medium to slow the photons. Having said that, it has been suggested that in the early universe the maximum speed of light was actually faster than 299,792,458 m/s and has slowed to its current maximum speed. Sources: Spatially Structured Photons that Travel in Free Space Slower than the Speed of Light - Science, Volume 347, Issue 6224, Pages 857-860, February 2015 (free preprint) Critical Geometry of a Thermal Big Bang - Physical Review D, Volume 94, Issue 10, November 2016 (free preprint)
  8. Superluminous SNe have been measured with an absolute magnitude of -23, 50 times brighter than your typical Type Ia SNe, but they are much rarer than the "sub-Chandrasekhar" Type Iax SNe. Superluminous Type Ia would throw off our distance by making it appear closer than it really is, which does not appear to be our problem. Our issue with an accelerating universe is because these so-called Type Ia SNe are appearing further away than they should. Which would be the result if you were looking at a Type Iax SNe with an absolute magnitude of -14.2 but calculated its distance based upon an absolute magnitude of -19.46. We can distinguish the difference between Type Ia SNe and Type Iax SNe, but only with sufficient data. We need more than just the light-curve. A full spectrum is required, for example, in order to determine the velocity of the SNe ejecta. The ejecta of all Type Iax SNe is less than 10,000 kps, while the ejecta of all Type Ia SNe exceeds 10,000 kps. There are additional ways the two different SNe can be distinguished, but only if we have the data. Unfortunately in many cases astronomers only obtain the light-curve and no spectrum, then make an assumption based upon that light-curve and its red-shift on the type of SNe it can be. I'm not sure if there is a means to distinguish the difference between a "Super-Chandrasekhar" superluminous Type Ia SNe and a normal Type Ia SNe. There has been some suggestions that these superluminous Type Ia SNe are the result of the rapid spin rate of the progenitor. While that makes sense, I am not sure how we would be able to determine the rotation of the progenitor after the fact. Sources: 'Super-Chandrasekhar' Type Ia Supernovae at Nebular Epochs - Monthly Notices of the Royal Astronomical Society, Volume 432, Issue 4, 11 July 2013, Pages 3117–3130 Superluminous Supernovae at Redshifts of 2.05 and 3.90 - Nature 491, Pages 228–231, November 2012 (free preprint) Type Iax Supernovae: A New Class of Stellar Explosion - The Astronomical Journal, Volume 767, Number 1, March 25, 2013 Gone in a flash: Supernovae in the survey era - Astronomy & Geophysics, Volume 54, Issue 6, Pages 6.17–6.21, December 2013 A Luminous Peculiar Type Ia Supernova SN 2011hr: More Like SN 1991T or SN2007if? - arXiv 1512.03995, January 2016
  9. Parallax is without a doubt the most accurate means of measuring cosmological distances, but as you correctly pointed out, it does have its limitations. Beyond parallax the methods used to measure distance becomes less reliable. Classical Cepheid variables are perhaps the second best source for measuring distance, providing you can distinguish them from anomalous Cepheid variables, RR Lyrae variables, or double-mode Cepheid variables. That should get you out to just about a million parsecs. Beyond about a million parsecs there is only two methods used to measure cosmological distances, Type Ia SNe and red-shift. Both have issues. Red-shift is great for determining how fast an object is moving relative to us, but not so good for determining distances except in the most general terms. Back in the 1990s we use to think the Type Ia SNe was our "Standard Candle," with a peak absolute magnitude of -19.46. However, we have since discovered "superluminous" Type Ia SNe in 2006 and subsequently, and we developed a whole new classification of supernovae in 2013 - Type Iax. Furthermore, there is between 18% and 48% chance that those supernovae that were classified Type Ia SNe prior to 2013 are in error and should actually be the much dimmer Type Iax SNe. Which brings into question not just the age of the universe but the existence of Dark Energy and this whole "acceleration" process. Dark Energy could simply be a mistake based upon our erroneous assumption that all Type Ia SNe were the same. The exact same mistake Edwin Hubble made in 1927 when he attempted to calculate the age of the universe using Cepheid variables as his "Standard Candle."
  10. The link above is bogus. I must have accidentally posted the wrong URL. Below is the correct link. It is a free article. Type Iax Supernovae: A New Class of Stellar Explosion - The Astronomical Journal, Volume 767, Number 1, March 25, 2013
  11. Your assertion is correct. The more observations that are made, the more accurately the asteroid's orbit can be calculated. Asteroids of such small size (~30m) are extremely difficult to detect. Even when found trying to find it again can be problematic. Yet these are the asteroids that are most likely to impact Earth in the short term. Approximately 100 tons of dust and sand impacts the planet daily. Asteroids the size of automobiles burn up in our atmosphere annually on average. NASA estimates that only once every 2,000 years an asteroid 300 meters in diameter impacts the planet. In order to come up with a means of mitigating the problem, a great deal about the asteroid needs to be known. Such as its density and composition. Is the asteroid a stereotypical carbonaceous chondrite (C-type), made of mostly metals (M-type), or a rubble-pile loosely held together (S-type)? Each different type would require a different form of mitigation on our part. That is assuming we had enough time to make such observations and time enough to act which, considering the size of the NEO, seems highly unlikely. NASA has the asteroid 2012 TC4 passing Earth today at 26,000 miles (~42,000 km) with a diameter between 15 meters and 30 meters. As the name suggests, it was first discovered in 2012 by a ground-based telescope in Hawaii, but then they lost it. It was rediscovered again, as you say, in July 2017. I was able to find out a great deal about asteroid 2012 TC4's orbit, however, I was unable to find out anything about the composition of the asteroid. Sources: Asteroid Fast Facts - NASA, March 31, 2014 Asteroid Tracking Network Observes Oct. 12 Close Approach - NASA, October 10, 2017
  12. First and foremost you need to understand that both "Dark Matter" and "Dark Energy" are merely placeholders, or labels, for something that we do not understand. It does not mean that either are "dark." They are only "dark" because we do not understand either. So they are really a description of our ignorance than anything real. As Janus correctly pointed out, Dark Matter and Dark Energy are completely unrelated. Dark Matter's history goes back to the 1930s. Fritz Zwicky first discovered the unusual rotational periods while working on galaxy clusters. It went largely unnoticed until the 1970s when Vera Rubin began studying galactic rotation. For some unexplained reason, galaxies were rotating far faster than they should be for the amount of visible matter that they have. Galaxies were rotating as if they had considerably more mass, mass that did not react to light. Hence the term "Dark Matter" was created to label this invisible matter. Since the late 1970s there has been a search for this missing matter. We can identify the effects Dark Matter has, such as the rotation of the galaxies, and also gravitational effects that causes light to bend, but we are no closer to identifying what Dark Matter actually is. There have been lots of theories, from Massive Compact Halo Objects (MACHOS) to Weakly Interacting Massive Particles (WIMPS), but so far none of them have panned out. In the case of Dark Matter we have something tangible and observable that we have not yet been able to explain. We have even made maps of Dark Matter using the light as it bends passing through such a strong gravitational field. We just can't see it, or explain what it is. Dark Energy, on the other hand, is something completely different. The term "Dark Energy" came along in the 1990s in an attempt to explain why the universe was not just expanding, but accelerating. Vesto Slipher first discovered galactic red-shifts in 1912, but it took Edwin Hubble to correlate these red-shifts into distance. While not a very accurate means of determining distance, it was sufficient to identify that galaxies were moving away from each other, and the further away they were the faster they appeared to be moving. In 1927 Georges Lemaitre, using Einstein's 1915 Theory of General Relativity, came up with his "Primordial Atom", which would be latter derisively referred to as the "Big Bang" by its biggest critic, Fred Hoyle. This debate on whether the universe was static and everlasting or had a beginning continued until 1964. When the cosmic background radiation was detected in 1964 it was the crucial evidence needed to sway the majority of astronomers and astrophysicists to accept the "Big Bang." Numerous attempts have been made to determine the age of the universe, beginning with Edwin Hubble. Unfortunately Hubble's initial estimate at the rate the universe was expanding (also known as the "Hubble Constant" today) was 500 km/s/Mpc or about 153 km per second per million light-years, which gave him an estimate of ~2 billion years. Hubble's mistake was his use of Cepheid variables as a "Standard Candle." We have since substituted Type Ia Supernovae (SN) to be our new "Standard Candle" and the current age of the universe (13.813± 0.038 billion years), making the Hubble Constant 67.31± 0.96 km/s/Mpc or ~20.65 km per second per million light-years. This is also where "Dark Energy" first makes its appearance. During the 1990s a concerted effort was made to record as many Type Ia SN as possible, and when the distances to these Type Ia SN were measured they concluded that the universe is not just expanding (as Hubble noted), but accelerating. Unable to explain this acceleration they attributed it to some unseen, and before now, undetected form of energy which they labeled "Dark Energy." Since that label was created we have since discovered that Type Ia SN are not the "Standard Candle" astronomers originally presumed them to be. Originally it was assumed that all Type Ia SN had an absolute magnitude of -19.46. However, in 2006 we discovered the first of several "superluminous" Type Ia SN. Then in 2013 a whole new classification of supernovae was created. This new classification, Type Iax SN, had an absolute magnitude ranging between -14.2 and -18.9, much dimmer than Type Ia SN. Furthermore, it is estimated that between 18% and 48% of all the Type Ia SN prior to 2013 have been misclassified and should actually be Type Iax SN. Which calls into question the Type Ia SN data collected during the 1990s used to calculate the age of the universe and its alleged acceleration. Exactly like Hubble's mistake using Cepheid variables as his "Standard Candle" in 1927 to determine the age of the universe, our understanding of "Dark Energy" could be attributed to the Type Ia SN we also mistakenly thought was a "Standard Candle" in the 1990s. We can distinguish the difference between Type Ia SN and Type Iax SN with sufficient data, but identifying "superluminous" Type Ia SN and distinguishing them from normal Type Ia SN is another matter entirely. Which means that there is no such thing as a "Standard Candle" in astronomy. Sources: A History of Dark Matter - arXiv : 1605.04909v2, May 24, 2016 WIMPs & MACHOs - Encyclopedia of Astronomy & Astrophysics, 2002 [PDF] A Brief History of Dark Energy - Astrophysics & Space Science, Volume 319, Issue 1, January 2009 (free preprint) What is the Hubble Constant? - Space.com, March 21, 2014 Type Iax Supernovae: A New Class of Stellar Explosion - The Astronomical Journal, Volume 767, Number 1, March 25, 2013 A Comparative Study of the Absolute Magnitude Distributions of Supernovae - The Astronomical Journal, Volume 123, Number 2, 2002
  13. When Congress created the NEO Search Program in 1998 they tasked NASA with finding 90% of the near-Earth asteroids that are one kilometer or larger. Then in 2005 Congress extended NASA's objective to include 90% of the NEOs larger than 140 meters. While the majority of NEOs have been identified via ground-based telescopes, they are not the only sources. Both WISE and NEOWISE were space-based infrared searches for NEOs before their cryogens were exhausted by 2010. It is a question of size. Since 1998 NASA has discovered ~98% of the NEOs that are one kilometer or larger. The percentage of known NEOs drops according to their size. At 140 meters in diameter fewer than 1% are known. However, while a 140 meter diameter meteorite impact could easily wipe out a large city, it would not cause an extinction level event. What was meant by the asteroid approaching from the "daytime sky" is that the asteroid approached Earth from the direction of the sun. Even with infrared sensing satellites we would not be able to see something approaching Earth from the direction of the sun, unless the satellite was closer to the sun than the NEO. It is our thermal blind-spot. Depending on the density and composition of the NEO, it will need to be between 20 and 25 meters in diameter in order to impact with the surface and form a crater. The Chelyabinsk meteor came very close to impacting the planet and it was estimated to be just over 15 meters in diameter. In order to be the cause of an extinction level event the NEO would have to be very large indeed. The asteroid that impacted the planet ~65 million years ago was estimated to be 12 kilometers in diameter. Currently, the known NEO with the highest probability of impacting Earth is 2010 RF12. Sometime between 2095 and 2117 there is a 5% chance that the asteroid may impact Earth. At only ~7 meters in diameter the NEO does not pose much of a threat. The odds of an unknown NEO causing an extinction level event is extremely unlikely considering the size it would have to be. However, it is only a matter of time before a 50 to 100 meter NEO that we didn't know about impacts the planet and could very possibly kill millions if it impacts a major city. Sources: NEO Search Program - Jet Propulsion Laboratory, Center for Near-Earth Object Studies Sentry: Earth Impact Monitoring - Jet Propulsion Laboratory, Center for Near-Earth Object Studies Absolute Magnitudes of Asteroids and a Revision of Asteroid Albedo Estimates from WISE Thermal Observations - Icarus, Volume 221, Issue 1, September-October 2012, Pages 365-387 (free preprint) The International Astronomical Union Minor Planet Center Asteroid Impact Effects and their Immediate Hazards for Human Populations - Geophysical Research Letters, April 19, 2017 (free preprint)
  14. First, it is obvious that you did not read Tappert et. al because he cites numerous sources. In fact the paper lists five pages of references. Tappert et. al even includes your prior reference of Berner, multiple times. Second, they are not my figures any more than your reference to Berner's data is your figures. If you have an issue with the peer-reviewed paper I provided, take it up with the author. At least I cited a credible source. Where is your citation?
  15. Your photo could be anywhere, and it is clearly south of the tree line. Kolari, Finland, is only a few kilometers north of the Arctic Circle (67° 19' 50'N), not the 200 km north of the Article Circle that Inivuk is located. The photo I displayed was of the village of Inuvak itself, and the surrounding area. There were no trees, just alder bushes and shrubs. Just as there are no trees anywhere on the northslope in Alaska. I should know, I live in Alaska and have worked on the northslope for years. There are absolutely no trees north of the Brooks Mountain Range in Alaska. I do not know why you insist that trees continue to grow beyond the tree line, but that is not the case. The tree line in Alaska is at ~68°N. The tree line in Canada's Northwest Territory is at ~69°N. The tree line in Canada's Nunavut territory is at ~61°N. The tree line at Canada's Labrador Peninsula is at ~60°N. The tree line in Greenland is at ~64°N. The tree line in Norway is at ~70°N. The tree line in central Siberia is ~66°N. The tree line in eastern Siberia (Kamchatka and Chukotka) is at ~60°N.
  16. It may be the first point to be hit by sunlight in Australia, but not in the world. It really depends on the time of year you are talking about because of Earth's 23.5° tilt. On Summer Solstice the very first landmass to be hit by sunlight is Semisopochnoi Island located at 51° 57' 05" North by 179° 36' 03" East. Semisopochnoi Island is one of the Rat Islands in the Aleutian Island chain in Alaska. https://en.wikipedia.org/wiki/Semisopochnoi_Island Even New Zealand, at 41° 17' South by 174° 27' East, gets the morning sunlight before Australia. FYI, Semisopochnoi Island is in the New Zealand Time Zone, but just slightly further east.
  17. Stable Carbon Isotopes of C3 Plant Resins & Ambers Record Changes in Atmopsheric Oxygen Since the Triassic - https://www.eas.ualberta.ca/wolfe/eprints/Tappert_GCA_2013.pdf Except that your assumptions are not supported by the evidence. Atmospheric oxygen levels during the Triassic and Jurassic were between 12% and 13%, and dropped even further to between 10% and 11% during the Cretaceous. At the end of the Cretaceous the oxygen levels spike back up to 18%, but are still lower than today's level. Hence, atmospheric oxygen levels played absolutely no role in determining the size of the dinosaurs. Stable Carbon Isotopes of C3 Plant Resins & Ambers Record Changes in Atmopsheric Oxygen Since the Triassic - https://www.eas.ualberta.ca/wolfe/eprints/Tappert_GCA_2013.pdf
  18. No, actually, you are not finding "decent-looking trees" near Inuvik. This is what Inuvik in the Northwest Territory actually looks like: Not a single tree to be seen as far as the eye can see. I don't know where "Kolari" is located, but clearly it is not as far north of the Arctic Circle as Inuvik.
  19. It may take longer than you think. It isn't just the climate that keeps the trees from growing, although that is the biggest contributor. The amount of sunlight is also a factor. The tree line stops just north of the Arctic Circle ( 66°33′46.8″ N) and just south of the Antarctic Circle ( 66°33′46.8″ S). The trees get smaller and more spaced apart the closer one gets to the poles. Clearly climate is a major factor, but the lack of sunlight for as long as 90 days at a time is also a factor. The northern forests of Russia, Alaska, Canada, Norway, and Sweden all have tree lines that stop just a few miles north of the Arctic Circle, even though there is still arable land further north. The north-slope of Alaska is completely treeless, even though the southern interior of Alaska is far colder during the winter. Lichen and other tundra plants seem to do better under such conditions than trees. We have to remember that when the continent of Antarctica was lush with forests it was not located at the South Pole, but much further north in a much warmer (and better lit) climate. Eventually the Antarctic continent will move away from the South Pole, but we are talking tens of millions of years from now.
  20. What is tenuous or suspect about making valid observations? Were there not large reptiles, dinosaurs, and mammals on the large landmasses? Did they not get smaller as the landmasses got smaller? In extreme cases, when the landmass was so small we have examples of dwarf species adapting to that environment. Atmospheric oxygen levels were between 12% and 13% during the Triassic and Jurassic, and dropped to between 10% and 11% during the Cretaceous, so atmospheric oxygen levels could not have been the cause for the size of the reptiles and dinosaurs during this period. What part of this line of reasoning is "highly suspect" to you?
  21. Atmospheric oxygen levels during the Triassic and Jurassic (between 140 and 250 million years ago) ranged between 12% and 13%. At the Jurassic-Cretaceous boundary (140 million years ago) the oxygen levels gradually dropped to between 10% and 11% over the course of the next 40 million years. Atmospheric oxygen levels were gradually beginning to increase again and then right at the end of the Cretaceous, when the dinosaurs become extinct 65 million years ago, atmospheric oxygen levels spike up to 18%. For the next 25 million years or so (between 40 and 65 million years ago) the atmospheric oxygen levels fluctuated wildly between 12% and 20%, until about 40 million years ago (about the same time India collided with the Asian continent) the atmospheric oxygen levels stabilized at 21%. Yes, we could breath. OSHA considers oxygen levels below 19.5% to be "deficient and immediately dangerous to life or health." But humans could survive until oxygen levels got to 6%, then that becomes fatal. However, at between 10% and 14% humans become mentally impaired due to lack of oxygen. This should not be confused with altitude sickness. Altitude sickness is due to the lack of atmospheric pressure. Hypoxia is the result of not enough oxygen being absorbed by the body. Source: Stable Carbon Isotopes of C3 Plant Resins & Ambers Record Changes in Atmopsheric Oxygen Since the Triassic - https://www.eas.ualberta.ca/wolfe/eprints/Tappert_GCA_2013.pdf
  22. I found the paper to be an accurate representation of what I have read from other sources. Toward the end of the Carboniferous and the formation of Pangaea, combined with our fourth ice-age at that time, the atmospheric oxygen levels began to decline. When that ice-age ended approximately 270 million years ago atmospheric oxygen levels were already down to ~18% with atmospheric carbon dioxide levels between 250 and 350 ppmv. That is also when temperatures began to rise, reaching between 35°C and 40°C. Contrary to popular belief, there were three main extinction events between 270 and 250 million years ago, and each of those three Permian extinction events (spaced between 9 and 11 million years apart) were larger than the extinction event that killed the dinosaurs. When the Siberian Traps began erupting 248 million years ago the particulates in the atmosphere helped cool off the planet and increased carbon dioxide levels significantly (by as much as 1,200 ppmv according to some sources), but atmospheric oxygen levels would take longer to increase. While atmospheric oxygen levels has certainly determined the size of arthropods, I am not sure the same thing applies to reptiles or dinosaurs. We have evidence of large arthropods during the Carboniferous, when atmospheric oxygen levels were as high as 33%. Even during the Silurian and Devonian, when oxygen levels spiked to 24%, there were 3 meter long arthropods. The atmospheric oxygen levels would drop again towards the end of Devonian, which is also when the giant eurypterids went extinct. What seems to matter more, with regard to the size of reptiles, dinosaurs, and even mammals, is the amount of space they have, not the amount of oxygen. Reptiles, dinosaurs, and mammals get bigger and bigger the more space they are given, irrespective of the amount of atmospheric oxygen that is available. During the Triassic the massive Pangaea continent was beginning to break up, but the super-continents of Gondwanaland and Laurasia still existed so they could start getting large during this period. When Gondwanaland and Laurasia started to break apart into South America, Africa, North America, and Eurasia about 100 million years ago it also ended the rein of the large sauropods. Life on land would never again get that large, and it had nothing to do with atmospheric oxygen levels. See also "The Silurian-Devonian: How An Oxygen Spike Allowed The First Conquest of Land", from The National Academies of Sciences, Engineering, and Medicine, Chapter 5 - https://www.nap.edu/read/11630/chapter/7
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