THE DEPTHS OF THE OCEANS: INCOMPATIBLE WITH A GLOBAL FLOOD MODEL
Created April 5, 2002
Updated October 2005 (fixed links)
attempting to harmonize the notion of a Noachian flood with modern geology,
young earth creationists are now forced to explain continental motions in a
plate tectonic framework. The model that is held forth most often is the 'catastrophic plate tectonic' model of Baumagardner1. This model posits runaway subduction of pre-flood oceanic seafloor as the driving force for rapid plate reconfiguration. Baumgardner adopts, without discussion, the Pangea model of modern Geology2. Baumgardner also asserts that ALL ocean floor (present-day) was formed during the flood (~4000 years ago)
The notion of Pangea was formulated by Wegener in the early 1900's. Wegener built on earlier works from the 1800's, but was the first to argue cogently in favor of the Pangea supercontinent. Wegener's conclusion was largely based on the presence of climatic indicators (glacial deposits etc) whose present location could be best explained, he felt, by polflucht ('flight from the poles'). Other data that suggested continental motion was the shape of the South American and African coastlines and some faunal evidence. Wegener's notion was soundly criticized by the geologic community because the oceans were thought to be old and thick and Wegener had no mechanism to drive continents through this thick oceanic crust. Nevertheless, such geologic dignitaries as Alex du Toit (S. Africa), Arthur Holmes (Edinburgh) and Sam Carey (Australia) thought that Wegener's idea had merit. In fact, Holmes suggested that mantle convection might be a suitable driving force for continental drift. Since Wegener's days, Pangea has been meticulously reconstructed using paleoclimatic indicators, geochronology, field geology, paleontology, paleomagnetism and magnetostratigraphy and the matching of paleobathymetric contours of the ocean floor3. Many of the fields of study used to reconstruct Pangea are vociferously attacked by creationists (for example radiometric dating and paleontological correlation); thus I refer to the creationist supercontinent as Pangea-Noachia in order to distinguish it from the real Pangea. This paper focuses on some of the implications of rapid continental drift proposed by Baumgardner. In particular, the paper will focus on paleobathymetry and modern bathymetry of the ocean floor and its incompatibility with the catastrophic models of Baumgardner.
One of the critical innovations and developments during the infant days of plate tectonics was the discovery of a large circum-global belt of undersea mountains (the so-called mid-ocean ridge system). These ridges are topographically elevated above the surrounding seafloor (see figure at the top of this page). The reason for their topographic expression is that they are active volcanic centers and they are thermally buoyant (compared to the surrounding seafloor)4. Harry Hess of Princeton University proposed that this bathymetry (along with other observations) was best explained by sea-floor spreading (the ridges were the source of new seafloor). Vine-Mathews and Morley collected magnetic profiles across the ridges and found them to be symmetric about the ridges. Subsequent radiometric dating and correlation with land records demonstrated that the crust grew progressively older with distance from the ridge axis4,5. Moreover, Parsons and Sclater (1977) showed that simple models of oceanic crust cooling via conduction fit the paleobathymetry of the oceans very well. The model predicts that older oceanic crust should thermally relax (via conduction) resulting in deeper bathymetry as distance from the ridge is increased. Furthermore, the analysis of conductive heat flow allows excellent estimates for sea floor depth in relationship to the speed at which subduction or spreading occurs6. Mathematically, the depth of the seafloor with age/distance/velocity is given by Equation 17:
The equation, in simple terms, predicts that the depth of the ocean will increase with the square root of the distance from the ridge. In mainstream geology, the distance is also age dependent. This must also be true in the creationist argument, though the age differences would be no more than 6000-10000 years. The equation produces a profile similar to that shown below:
Figure 1:Generalized thermal relaxation profile away from a ridge crest using equation 1 and a spreading rate of 5 cm/year.
These equations can be reformulated to account for the rate at which subduction or spreading occurs to generate profiles of the ocean floor topography using a variety of input parameters. For example, the formula used to estimate sea-floor topography that is dependent on the age of a subducted slab is given by8:
The solution to equation 2 has a similar form to equation 1 and is given by:
We can now use these equations to predict the depth of the seafloor using creationist assumptions. The simplest exercise is simply to conclude that the spreading took place rapidly (for example, in order to open up a 4000 kilometer wide ocean during the year of the Noachian flood, the spreading rate must have been on the order of 4 x 108 cm/year (this means the oceans were growing at about 750 cm/minute!!). Using this spreading rate in equation 1 yields the following result:
Figure 2: Depth of seafloor expected today based on the ocean
forming during the year of the Noachian flood
and cooling via conduction until today.
Of course, there can be several arguments made by creationists to counter the physical result shown in Figure 2. The first is that the assumption that the entire ocean opened during the year of the flood is untrue. Therefore, creationists may contend, that spreading was initially fast and has decayed to the rates we observe today. This can be easily accommodated in the model through the placement of a decay function into EQN1 for spreading rate . While this 'decay function' can account for the slowing of spreading rates since the flood, it does not result in reasonable oceanic depths. In fact, one can develop several iterative models and still never come up with the profiles we observe today. In order to approximate the depth profiles in today's ocean and maintain the rapid spreading model, it is possible to vary some of the other parameters in the equation. An example of some other variations (and comparison to today are given below:
Figure 3: (top) A different view of the flood model (inverted to reflect +depth below ridge) using an exponential decay for spreading rate (middle) graph using standard geology and (bottom) flood model generated by increasing diffusivity by a factor of 105. Note that in the bottom figure the axis is mislabeled Ma and it should be (years).
The bottom figure comes close to approximating today's sea level profile, but the result is only a mathematical trick9. Finally, young earth creationists could argue that conductive models are inappropriate for the Baumgardner model since it relies on vigorous convective processes10. Indeed, I would suspect that this is the only recourse possible to salvage the runaway subduction model. The problem with convective models is that they would not generate an oceanic-depth profile consistent with conductive cooling. Convective heat transport is efficient and fast and would result in a profile that is basically flat during the rapid spreading portion of the flood. It would presumably change to a conductive regime sometime post-flood. In qualitative terms, the profile might look like:
FIGURE 4: Hypothetical ocean profile assuming rapid
convective cooling during the flood followed by conductive
cooling sometime after the flood. The problem is that this does not match the observations AND the rate of conductive
cooling needed to produce the conductive part of the curve results in still very fast spreading rates!
In essence, the problem for young earth creationists is to develop a self-consistent model of rapid spreading that can yield the bathymetric profiles observed in the current ocean floors. Modern geology has already done so and the conductive cooling model of the ocean floor fits perfectly within the old earth paradigm.
The conductive cooling predicted by modern geology also matches the age distribution on either side of the ridge. The predicted age of a piece of ocean floor based on conductive cooling is a near perfect match for the radiometric and magnetostratigraphic age11 of the ocean floor. These observations are not consistent with the hypothetical profile shown in Figure 4. For example, radiometric ages in the convective region would be nearly identical and would show greatest change in the conductive region. This is contrary to what we observe. In short, the observed bathymetry is a near perfect match for an old earth model and seriously challenges the model proposed by Baumgardner and other advocates of rapid drift.
Other Essays by Author:
1. Baumgardner, J.R., 1994, RUNAWAY SUBDUCTION AS THE DRIVING MECHANISM FOR THE GENESIS FLOOD. It is important to note that the subducting material in Baumgardner's model would be balanced by the extrusion of new sea floor during the breakup of 'Pangea-Noachia".
2. Wegener, A., 1912. Die entstehung der kontinente und ozeane, Petermans Mitteilungen, 185-195.
3. Tarbuck and Lutgens, Earth, 2001.
4. Davies, Dynamic Earth 2001.
5. Glen, The road to Jaramillo, 1982.
6. Turcotte & Shcubert, Geodynamics 2nd edition 2002.
7. =density of the mantle (3300 kg/m3); =density of water (1000 kg/m3);=coefficient of thermal expnasion (3 x 10-5 K-1); =Differential temperature between mantle and surface (taken as 1300 K); =thermal diffusivity (1 mm2/sec);=distance from ridge (meters);=velocity of spreading
8. Parameters are the same as in reference 7, =average age of subduction. Note: K is for Kelvin (a measure of temperature with the same scaling properties as celsius (i.e. 1 C = 1 K; however for example 0 C= 273 K).
9. Thermal diffusivity is related to how far/fast heat is transported. Extreme values of diffusion required to generate the thermal profile shown in Figure 3 indicate that convection is vigorous and therefore the conduction equations are no longer valid. In essence, the equations will give an answer that is physically impossible. In fact, Baumgardner in defending his model on another attack, Baumgardner admits:
Baumgardner: “If these critics had read my papers carefully, they would have learned that a low thermal diffusivity actually aids the runaway mechanism. Whether or not the runaway occurs at all depends on a competition between heat production due to deformation and heat loss due to thermal diffusion. Low, rather than high, thermal diffusivity assists this process"
10. Baumgardner's model relies on unrealistic viscosity values and extreme values for other parameters in order to generate runaway subduction. There is no evidence to support the values used in the model although the computer will unashamedly generate the answer!
11. Creationists argue that magnetic reversals are (a) not real or (b) happen quickly during the flood. Unfortunately, the magnetostratigraphic pattern observed in the ocean floor coupled with the thermal conductive (or convective) model does not support either (a) or (b). For example, creationists could argue that reversals happened quickly during the flood yet the edges of the Atlantic Ocean (cretaceous age) show little in the way of reversals (Cretaceous Long Normal Interval). If (b) is true and it is true that reversals no longer happen, then we should only see them in the convectively cooled ocean floor. However, we see them all the way to the ridge. There are other problems associated with the magnetic polarity patterns in the ocean and on land for the young earth creation model that will be discussed in another essay.