Ocean Floor Sediment as a Creationist Clock

By Jason Tentinger

The fact that most of the Earth is covered in water has spurred much interest in the world's oceans. For many years, scientists have studied the ocean's creatures, the effects of introducing chemicals to the water, and the geologic floor of the world's vast oceans. One creationist believes that the floor of the ocean provides evidence that the earth is much younger than the generally accepted age of 4.6 billion years. This paper will provide an explanation of his claim, as well as evidence and arguments provided by mainstream scientists which causes them to reject this young-earth creationist's clock.

Before these claims can be considered, a brief explanation of plate tectonics is in order. The theory of plate tectonics states that the lithosphere, which is the layer of Earth that includes the continental and oceanic crusts, is divided into seven large plates and several smaller ones. These plates are in constant motion. Earthquakes and volcanic activity are caused by the movement of plates and interaction at their boundaries. Plates that move apart from each other form divergent boundaries, while plates that move towards one another form convergent boundaries. convergent ocean-continent plate boundaryConvergent boundaries cause lithospheric subduction, the destruction of the sea floor, which is a key aspect of the supposed clock used to date the earth by measuring the depth of mud on the ocean floor. When two plates converge, one slides beneath the other, taking the sediment present on the ocean floor with it, as shown in the diagram below (Duxbury et al. 2005:69). Plates that are sliding past one another form transform boundaries.

Rivers, streams, and winds deposit twenty billion tons of sediment from the land into the ocean each year. Lithospheric subduction is one major way that this sediment is ultimately removed from the ocean floor. Dr. D. Russel Humphreys, a physicist at the Institute for Creation Research, believes that subduction removes only one billion tons of sediment from the seafloor every year, so if the oceans are billions of years old there should be much more sediment present on the ocean floor than the current thickness, which averages around 400 meters. He claims that at the current rate of subduction and sediment deposition, it would take, at most, only twelve million years for the ocean floor to reach its current level of sediment. Therefore, he contends that the Earth cannot possibly be older than twelve million years. He argues that the timeline proposed in the Book of Genesis is more realistic than the geological timeline accepted by most scientists (Humphreys 2005).

Mainstream scientists contend that the present amount of sediment on the ocean floor does not conflict with the generally accepted age of Earth. According to David E. Thomasm (1998), Humphrey's proposed geologic clock is overly simplistic and involves a misunderstanding of sedimentary processes. He writes:

The depth of sediments on the ocean bottom is not a uniform 400 meters, but varies considerably. And much sediment never gets to the ocean floor, but is trapped instead on continental slopes and shelves, or in huge river deltas. Over the years, some of these continental slopes can accumulate several kilometers of sediment, while others can even become part of mountain ranges in continental plate-to-plate collisions. Neither erosion nor subduction are expected to be constant processes over millions of years, and they are simply not good clocks. Humphrey's strawman ocean floor does not prove the Earth is young.

Humphreys states that "An alternative (creationist) explanation [for the amount of sediment on the ocean floor] is that erosion from the waters of the Genesis flood running off the continents deposited the present amount of sediment within a short time about 5,000 years ago" (Humphreys 2005). If this catastrophic event was the cause, one would expect the ocean bottom to be covered in a single kind of sediment. However, the type of sediment on the ocean floor varies considerably and matches a uniformitarian model.

According to Duxbury et al. (2005), seafloor sediments can come from one of four places: preexisting rocks, marine organisms, seawater, or space. Sediments that come from preexisting rocks are termed terrigenous sediments. They include the sand, rock fragments, wood chips, and anything else that enters the ocean from the land. Rock powder may be suspended in the ocean for many years and eventually form clay on the ocean floor. Biogenous sediment is produced by marine organisms. This type of sediment includes siliceous ooze and calcareous ooze and is dependent upon the biomass and skeleton formation of organisms inhabiting the water. According to Rachel James (2005), "Diatom oozes generally predominate in deep waters at high latitudes and in areas of coastal upwelling, whereas radiolarian oozes are found at low latitudes. The belt of siliceous sediments round the Antarctic consists of diatom ooze, whereas that in the equatorial Pacific is of radiolarian ooze." In places where diatoms and radiolarians are abundant in the ocean today, the sediment underneath them is composed of their skeletons, even to a great thickness. This is not consistent with a global flood model because such an event would have caused the seabed's sediments to be intermixed. Hydrogenous sediment is created by chemical reactions in seawater to form minerals that accumulate as sediment. Sediment created by objects from space, such as meteors, is called cosmogenous sediment (Duxbury et al. 2005:114-116).

global distribution of sedimentThe distribution of sediment is uneven because sediment derived from the continents stays mostly on the continental shelf, which is the area of shallower water around the continents and which is never subducted. There is also a much higher amount of sediment accumulation adjacent to deserts, where the wind blows continental sediment into the ocean. Humphrey also fails to account for the amount of debris that does not accumulate on the ocean floor. In fact, according to Rachael James (2005), only between one and ten percent of skeletal debris becomes sediment. The rest is dissolved in the ocean water either before reaching the seafloor or shortly afterward. The rate at which skeletal debris is dissolved in the water can also vary greatly with temperature, pressure, and carbon dioxide concentration (James 2005:58, Duxbury et al. 2005).

Because different sediments have different compositions, some accumulate faster than others, while some are more likely to dissolve in the ocean water. According to Rachael James (2005:59), "Close to continental margins where inputs of material from the land are high, terrigenous sediments can accumulate at rates as high as a few meters per thousand years, enough to obliterate any biological component. By contrast, the accumulation rate of siliceous ooze is of the order of a few meters per million years." Because of the variation in sediment type, and the consequent variance in accumulation rates, the depth of sediment in the ocean as a whole cannot be used as an accurate natural clock.

Humphrey's argument focuses on subduction at convergent plate boundaries. He overlooks what occurs at divergent plate boundaries, where new ocean crust is being formed. As two tectonic plates move away from each other, new sediment begins to be deposited on the new seafloor that is created by their boundary. The sediment on the young sea floor is not very deep because it has not had nearly as much time to accumulate. The older the ocean crust, the more sediment there is covering it. Therefore, the thickness of sediment on new crust can be used as crude type of geologic clock. The thickness of sediment is in any particular location is generally consistent with the age of the sea bed and the modern rate of accumulation in that region (Duxbury et al. 2005:113). By contrast, a world-wide flood would be expected to distribute a more uniform layer of sediment throughout the oceans.

Although the age of the ocean floor roughly corresponds to the amount of sediment accumulation, dating the seafloor and its sediments is not a good way to estimate the age of the Earth as Humphreys (2005) implies. Because the seafloor is constantly being created and destroyed, the ocean floor is actually much younger than the Earth as a whole. The oldest seafloor has been radiometrically dated to only about 200 million years (Duxbury et al. 2005:114), whereas continental rocks have been dated to four billion years, and the earth is thought to be about 4.6 billion years old (Dalrymple 2004). Therefore, the age of the ocean floor is not an accurate tool to measure the age of the Earth.

While Humphrey's claim that depth of sea floor sediment proves the Earth cannot be older than twelve million years may seem logical, there is a lot that he is overlooking. Yes, subduction is one major means by which sediment is destroyed, but that does not mean that measuring the depth of sediment and determining the rate of subduction versus sediment deposition will create an accurate natural clock. There are many factors that Humphrey does not take into account, such as sediment not reaching the ocean floor, sediment dissolving, uneven distribution of sediment, and the fact that sediment accumulation varies greatly with the type of sediment involved. Seafloor sediments also support uniformitarianism, rather than Humphrey's proposal of catastrophism, since the seafloor sediments closely match the regional sediments being deposited today.

Sources:
  1. Dalrymple, G. Brent. 2004. Ancient Earth, Ancient Skies. Stanford: Stanford University Press.
  2. Duxbury, Alyn C., Alison B. Duxbury, and Keith A. Sverdrup. 2005. The World's Oceans. 8th ed. Boston: McGraw-Hill.
  3. Humphreys, Russell. 2005. Evidence for a Young World. Acts and Facts, Impact Article #384, Institute for Creation Research.
  4. James, Rachel. 2005. Marine biogeochemical Cycles. 2nd ed. Boston: The Open University.