Monday Minute: Oceanic Crust? Not in a Young Earth!

What geologists have learned about the ocean floor over the past 70 years completely shifted our paradigms several times. First, decommissioned submarines discovered that the seafloor was not flat, but is covered in mountains, ridges, plateaus, valleys, and super deep troughs. This discovery was shocking in and of itself, because we expected that the calm conditions of the deep ocean might have yielded a smooth blanket of sediment over a featureless abyss, much like a vast, subaqueous desert expanse. The underwater topography of the seafloor (aka, its ‘bathymetry’) was readily explained, however, by the second discovery: oceanic crust was constantly being created by extensive ridge systems—where the seafloor was spreading apart—and it was constantly modified by massive volcanic systems (e.g. island chains and oceanic plateaus) and subduction at plate boundaries.

These discoveries in oceanography, which largely fueled the modern theory of plate tectonics, also coincided with the founding and expansion of the creation science movement. Early on, therefore, it was taken for granted that the oceans might have simply been created in place, perhaps accumulating some sediments in the wake of Noah’s flood. But as a more dynamic portrait of the oceans appeared, YEC evolved alongside. Notably, young-Earth interpreters of Genesis associated the “fountains of the great deep” (Gen. 7:11) with deep-ocean vents, without hesitation, despite that such features were wholly unknown to biblical authors and readers until the late 20th century. They further speculated that the ocean floor could have subsided after the flood, explaining the ultimate fate of the global flood waters.

Once the theory of plate tectonics, rejected out of hand by early authors such as Henry Morris, gained sufficient traction in geology, YEC’s were quick to adapt. Geophysicist John Baumgardner, with substantial support from ICR, committed to model how continents could have broken up and drifted apart in a matter of decades to centuries. His so-called ‘theory’ of Catastrophic Plate Tectonics swiftly gained popularity, because it seemed to be rooted in a meaningful physical model and a plethora of real-world data. According to Baumgardner, the ‘pre-Flood’ ocean floor subducted rapidly beneath the continents, driving Earth’s tectonic history—including the breakup of Pangaea and formation of mountain belts—on a decadal scale. Oceanic ridges formed in response to the stretching of the crust and quickly produced a brand new seafloor, which even recorded geomagnetic anomalies produced by the catastrophic assimilation of old crust deep into the mantle.

So long as one is unaware of the numerous problems created by Baumgardner’s conjecture, including the fact that it would leave the oceans unbearably hot and devoid of life, the scenario almost sounds plausible. One feature overlooked by the model, however, is the creation of new oceanic crust, which we observe today occurring at an extremely slow rate (millimeters per year, on average). First, there is no evidence that the rate of oceanic spreading varied by orders of magnitude at any point in Earth history. From one end of the ocean to the other, the basic structure and chemistry of oceanic crust looks pretty much the same as actively forming crust. As one moves away from active ridges, moreover, the temperature of the crust decreases rapidly, indicating that ample time has passed to allow for cooling of the rock.

More importantly, however, the characteristic chemistry of ocean crust reveals that it could not have been formed catastrophically, especially over the course of centuries. Take a look, for example, at the difference between granite (common in continental crust) and basalt (typical of oceanic crust). In granite, the individual crystals are relatively large well formed, because they cooled over a much longer period of time while buried deeply beneath the surface. But these rocks also vary in their composition. In short, basalt contains much less silica, a lower concentration of alkali metals (e.g. Na, K, Rb), and a much lower concentration of what are called Rare-Earth Elements. But all of these constituents, collectively called incompatibles, are concentrated in rocks like granite.

The main reason for this contrast lies in the fact that the upper mantle, from which ocean crust is formed, has been depleted over time by the formation of continental crust, which preferentially removes incompatible elements. Imagine, for example, the way a thin layer of fat develops on the surface of a slowly cooling pot of broth. As the layer develops, the underlying water becomes depleted in dissolved molecules of fat. In the same way, the chemistry of oceanic crust reveals a long history of Earth’s geochemical evolution.

Once oceanic crust is formed, it remains several hundred degrees celsius for millions of years. During this time, oceanic water is able to circulate through the rocks, exchanging certain elements (e.g. Na) for others (e.g. Ca) and modifying the minerals within the crust, after which it is expelled through hydrothermal vents. If the crust were formed catastrophically, less than 5,000 years ago, then not only would it still be exceedingly hot, but we should find active (or at least recently active) hydrothermal vents across the entire ocean floor. Today, however, they exist only near active spreading centers. This distribution is entirely consistent with the estimated age of our current ocean floor, which ranges from 0 to ~180 million years.

Young-Earth geologists take for granted the unique structure and chemistry of the ocean floor, which rather reveals a very long and complex history. Though having the appearance of scientific rigor, their catastrophic models of plate tectonics contradict the most basic features of oceanic crust. Every time you see a cross section of oceanic crust, therefore, be reminded that “Catastrophic Plate Tectonics” is not a scientific theory, but a hypothesis contrary to fact.

Note: Radiometric dating of the ocean floor is a powerful, independent witness to its great antiquity, but I have intentionally omitted those data here, simply for the sake of discussion. Even without radiometric dating, we can recognize that Earth’s oceans are indeed quite old.

Featured image from COSEE: “Age of the Ocean Floor”.

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