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Comments on AP article about prehistoric tropical arctic

  1. Jun 1, 2006 #1
    Scientists say Arctic once was tropical

    I don't know much about geology, but shouldn't this AP science writer have at least asked about the possibility that the location where these preserved tropical specimens were found may have been at a different position on the globe. Am I wrong to assume that 55 million years is a decent time scale for significant continental drift to occur?

    I just find it hard to believe that even in a very very warm earth that alligators and palm trees would survive in a region that is completely dark for several months each year. The latter for photosynthetic reasons, and the former for reasons that involve reduced food supply and probably freezing temperatures.

    Let me know if I am way off.
    Thanks in advance for any replies
  2. jcsd
  3. Jun 1, 2006 #2

    jim mcnamara

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    Yes, it's possible. Antarctica had extensive dinosaur populations and "tropical" plant populations as it moved South of the Antarctic Circle.

    The animals and plants adapted to colder, dark winters. Eventually it became so hostile terrestrial non-migratory animals completely died out. Ditto most plants. I think the flowering plant species count down there still requires only the fingers of one hand.

    There are boreal plant species that remain dormant for large parts of the year - from willows to cotton grass. They seem to be doing okay in terms of surviving long periods of darkness. As a modern example.
  4. Jun 1, 2006 #3
    It doesn't look like the arctic changed much since then. These are images taken from scotese.com, if you haven't been there it's an interesting site about Earth history.




    As you can see, between 66 and 50.2 million years ago the arctic wasn't too different from what it is today. Greenland does look a bit further south, but not south enough to explain 75F temperatures.

    I read in the artical that the carbon dioxide content in the atmosphere was much higher, does anyone have any compartive numbers on that? And it's curious that the arctic was this way immediately following the extinction of the dinosaurs.
    Last edited: Jun 1, 2006
  5. Jun 1, 2006 #4


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    "The 74-degree temperature, based on core samples which act as a climatic time capsule, was probably the year-round average, but because data is so limited it might also be just the summertime average, researchers said."

    Translation? Isotope ratios in the core samples are interpreted on some unspecified basis (bases); there is no mention of very restricted exchange of water, oxygen and carbon isotopes, with the Atlantic and Pacific basins of the time, and what corrections to isotope interpretations might be necessary --- alternatively, assigning a larger uncertainty to isotope-temperature proxies for closed basins. From the "temperature" record, one then applies the "one-parameter" climate model of the GW modelling groups to infer high CO2.

    AP reporter bright enough to know when the snow is flying? Not likely. Should science reporters add stock questions to their interviews? Yes. What questions are those? "What approximations and assumptions have you made to reach these conclusions; and, what other models and explanations are possible?"
  6. Jun 4, 2006 #5
    One of the most important questions to ask in this case would be about the Milankovitch cycles, especially how the earth was tilted on its axis at the time. One of the many things climatologists are ignorant about is that plant health doesn't depend on average temperatures but on temperature ranges. Different plants require different temperature ranges to live and function. Too hot or too cold and the plant may go into a dormant stage or even die. Many tropical plants are killed by prolonged exposure to subfreezing temperatures so I suspect that 55 million years ago the earth was not tilted enough to cause wintry conditions at the poles.
  7. Jun 5, 2006 #6


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    Didn't Lance Armstrong ride "Milankovitch cycles?" Or, wait, maybe they were one of Harley's competitors --- you presume too much of journalists --- that's the point behind the "stock questions."

    Forty years ago, the lunar ephemeris was "good" to 3ka either direction; good might have meant placing eclipses on a correct day, or it might have been some other criterion --- I didn't think to ask at the time. The physics is well understood; the quality, time span, and number of observations of earth-moon orbital dynamics aren't really up to a 55Ma extrapolation --- place limits on axial tilt, lunar precession and recession, earth axial precession rate, assorted other parameters? Yeah. Specify values? No.
  8. Jun 5, 2006 #7


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    I am constantly telling people it is always better to read the scientific literature rather than the news reports.
  9. Jun 9, 2006 #8


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    From Brown university,
    Glaciers formed in tandem, with the Antarctic icecap forming first, 45 million years ago.
  10. Jun 11, 2006 #9
    Isn't it odd that such a blatant geological anomaly goes by so quietly? Believe me, that palaeo science is rather numb now. Whatever hypothesis would have been sort of tolerable for the many enigmatic events of the Palaeocene Eocene Thermal Maximum, it's all void now. It's also clear that a runaway global warming scenario does not add up, simply because the Arctic is not global and many other places suggest termperature anomalies of 3-8 degrees celsius at that time, no more, whereas the Arctic suggest some 40-60 degrees temperature anomaly.

    Now if you want to understand what happened take a good look at this reconstruction (from the original article in Nature). Note in particular the sea strait separating Europe and Asia (yes, these are two continents from origine).

    Now, this is what could have happened:

    Last edited: Jun 11, 2006
  11. Jun 15, 2006 #10
    Milankovitch cycles refer to variations in the earth's tilt on its axis(without this tilt the amount of sunlight received each day at a specific location on eath would be the same throughout the year) differences in the shape of earth's orbit and the time of year when earth is closest to and farthest from the sun. Currently the earth is closest to the sun during the northern winter which means warmer winters and cooler summers in the the northern hemisphere.


  12. Jun 16, 2006 #11

    That sounds like prior to that time the earth didn't have a tilt to its axis in relation to the sun with the result that both poles received light from the sun throughout the year and seasons varied only because of the changing distance between the earth and the sun during the year. The formation of both ice sheets at the same time would indicate that the earth's tilt might be of relatively "recent" origin.
  13. Jun 16, 2006 #12
    The reasoning however is the other way around. If there is no tilt and no seasons, the polar region would indeed get sunlight all year but the angle of incidence is very shallow and the average temperature year round would be below freezing, allowing ice sheets to build up.


    The ice sheets are supposed to build when the tilt is minumum and the summers are to cool to melt all the ice that was formed in winter time.

    Consequently, if the tropical Arctic swimming paradise was to be explained by milankovitch cycles, it would require a very high tilt to get really warm tropical summers when the sun is high in the sky and does not set for the whole summer season. The organisms should be sturdy enough to survive the severe dark Arctic winters of course.

    But the Arctic and Antarctic were already warm in the Paleocene (65-55 Million years ago) and the temperature surging during the PETM for about 200,000 years (10 precession cycles), while the temperatures started to drop in a few million years in the Eocene. It seems rather unlikely that the Earth decided to tilt over for some odd period. But who knows.
  14. Jun 21, 2006 #13

    The important factor is that without a tilt there is no prolonged period without a source of heat which causes the ice buildup and would kill any tropical plants. The important environmental factor for tropical plants is the low temperature not the high one. Tropical plants do not necessarily benefit from very high temperatures, but may be easily killed by a hard freeze.

    The most northerly areas would not need to get all their heat directly from the sun, because air and water circulation could provide sufficient additional heat to keep air temperature above freezing is such air circulation does in many areas of the U.S. during winter.

    Without the periodic influx of extremely cold upper(winter) level air from the polar regions the atmosphere would be warmer over other areas. A warmer atmosphere would reduce the high cloud cover of ice crystals which can block sunlight without being likely to fall as snow or rain.

    Water carries a great deal of heat energy and so long as the surface isn't covered it carries that heat energy into the atmosphere when it evaporates. With sufficient water in the atmosphere the dew point could remain above freezing which would prevent freezing of plants. The suggestion you made earlier about warm water moving into the region would help keep the dew point high enough to prevent freezing. However, this movement would not keep the area sufficiently tropical if the area had the type of prolonged darkness that allows the land area to cool well below freezing and experience the type of high snowfall that would produce snow cover that would reflect spring sunlight back into space and delay reheating of the area. In fact the warm water might increase snow fall be continuing to release water into the atmosphere that would subsequently fall as snow on land areas.

    As for the cause of the tilt, one possibility might be an asteroid hit from above(or below) the plane of the solar system or possibly a series of hits in the polar regions. We usually think of asteroids making what could be considered a direct hit that produces a large crater. An asteroid coming from above or below the plane of the solar system might hit the earth a glancing blow and "bounce" off like a billiard ball. the hit might not need to cause an immediate full tilt, but cause a sufficient wobble to eventually lead to the tilt that occurred later.

    Considering that the earth is "top heavy" due to a greater amout of mass in the northern hemisphere, it might also be possible for a heavy body passing through from above or below the plane of the solar system to produce a gravitational attraction that might "pull the earth over"

    I believe that there is a theory that one of more of the gas giants might be a late arrival in the solar system. If so, earth might have at one time been orbiting closer to the sun than it is now which would have resulted in higher temperatures.
  15. Jun 26, 2006 #14
    I've been thinking more about the tilt issue. A heavy body might not need to collide with the earth to cause it to tilt on its axis. A passing heavy body with a magnetic field might be the more likely to have caused the tilt. A heavy body passing above the plane of the planet with its north pole "down" would have a repelling affect on the region of earth around earth's north pole which would tend to move that area away from the passing heavy body resulting in a tilt.
  16. Jun 26, 2006 #15
    Oops, getting out of control here. That's not physics. Passing heavy bodies do not change tilts of spin axes, which are extremely stabilized due to the gyroscopic effect, instead they change the orbits around the sun, something that should not have gone unnoticed in geology.

    The obliquity of the earth is highly stabilized albeit that it cycles a tiny bit with a period of 41,000 years, you can read all about it here:


    the cause of this tilt cycle is related to the precession cycle of some 25,700 years which is decribed here:


    The same theory predicts that when the moon recedes further and the spin of the Earth decreases that the precression cycle period will increase. When in two billion years the precession and axial tilt cycles have the same period, resoncance will occur which should lead to extreme axial tilt cycles, which is called the chaotic zone.


    This may change the Earth to make it the real identical twin of Venus but that's a different story.

    So there is little chance to do creative things with the axial tilt to explain the PETM. You could think of a True Polar Wander but that would lead to some other complications.
    Last edited: Jun 26, 2006
  17. Jul 3, 2006 #16
    A passing heavy body wouldn't permanently change a planet's orbit because that depends on the attraction of the other planets - although it might change the orbit of the moon such as by changing the distance from the earth. A heavy body that joined the solar system would permanently affect the orbits of the other planets. The earth's spin axis would be stable if it were a sphere rather than a kind of warped "pear" with its mass unevenly distributed with the distribution subject to variation including its "midriff bulge" around the equator.

    I hadn't really thought about the earth's tilt until this thread. The statement about the start of the ice caps raises the possibility that something must have changed with the earth's tilt being a strong possibility because such a change would allow prolonged cooling. the more I think about it the more I think that a body with a strong magnetic field would be more likely to change the tilt than would a gravitational affect.

    I have doubts about the polar regions retaining significant heat during a long dark winter even with warm water currents bringing in heat. Geothermal heating might have been playing a more significant role at the time either because the earth was warmer or because areas of heat were closer to the surface at the poles.
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