The Sediments of the Earth — are they old?

The following guest post was authored by Dr. Willy Fjeldskaar, a petroleum reservoir geologist and an adjunct professor at the University of Stavanger in Norway. He argues that even the temperature of sedimentary layers today provides ample evidence of their great antiquity. When oil companies construct a new well, temperature is measured from the surface to the bottom of the well to create a profile versus depth. This information is valuable to geologists, who use the age of sedimentary layers and their temperature to predict whether oil could have formed. As you might expect, temperature increases with depth, but the gradient depends on two variables: the amount of heat flowing from the upper mantle, and the thermal conductivity of the rock layers. If you place an aluminum pan on a gas burner, the cooking surface heats up almost immediately, because the flame is hot and aluminum is an excellent conductor of heat. Conversely, the center of a Thanksgiving turkey can take hours to heat up in a conventional oven. Along this reasoning, Dr. Fjeldskaar envisions two geological scenarios to perform a simple test. In the first, sedimentary layers were deposited over hundreds of millions of years. In the second, they were deposited in a single year less than 10,000 years ago. In each case, what might we predict the temperature of these rock layers to be as one drills down through them? In other words, how long has this turkey been in the oven?

In the sea offshore the Norwegian coasts, we find sedimentary layers of enormous thickness, in which oil and gas have been found. These sedimentary layers can be more than 10–15 km thick in the North Sea, the Norwegian Sea and the Barents Sea. These sediments have been dated to many millions of years old, but all dating methods are based on some unverifiable assumptions, and the uncertainty grows backwards in time. Nonetheless, scientists do their best to get reliable age measurements. They conclude that sediments have been deposited over a long time, layer upon layer. According to conventional radiometric dating, this occurred over many millions of years.

Figure 1: Section through the upper layers of the earth, showing sedimentary rocks down to 16 km below the sea bottom. This section is ~320 km long, with the Norwegian coast to the right. Beneath the sediments we find the Earth’s crust (brown) and the mantle (grey). The four boreholes and their depth are also shown. On the right side of the figure is shown the assumed geological ages of the sediments.

Figure 1 shows a section through the upper parts of the Earth (mid Norway), from the bottom of the ocean down to a depth of about 30 km. There are sediments down to ~16 km, which are color coded according to their age. The oldest sediments are dated to more than 100 million years old (for example, those indicated by green are assumed to be of Cretaceous age). The youngest sediments (at the top) are only thousands of years old, and have been deposited in connection with the Ice Ages.

Not everybody agrees that the sediments of the Earth are so old. The most widely known book arguing for a young Earth is “The Genesis Flood” by Whitcomb and Morris. None of the authors were geologists—Morris was an engineer and Whitcomb a theologian. In any case, they argued that nearly all sediment layers were formed in a global flood, which they assume took place less than 10,000 years ago.

As mentioned earlier, one can question the reliability of the dating methods. Therefore, I want to suggest another, more objective method to decide whether the sediments are young or old. The method that can be used to settle the age dispute is related to temperatures in boreholes in sedimentary rocks. Figure 1 shows locations and depths of 4 boreholes that have been drilled in the section from offshore mid Norway. In these wells different measurements have been taken, including temperature. One of these wells has been drilled down to a depth of 5 km. The temperature at the bottom of these wells has been measured to 90–150°C, depending on the penetration depth.

The temperature of the sediments is caused by the heat flow from the inner regions of the Earth. If you put a kettle with water on a hot plate, it will take some time for the water to be heated. A certain amount of time is also needed to heat sediments from the time they were deposited until today. The amount of time needed depends on the flow of heat from the inner regions of the Earth and on the thermal properties of the sediments. Both the heat flow and the thermal properties are relatively well known. The thermal properties of sediments are known precisely from laboratory measurements. The present heat flow is more roughly known, and it varies from 40 to 70 mW/m² off the coast of Norway.

Figure 2: Calculated temperature through the sedimentary layers. The geological ages shown in Figure 1 have been used in the calculations, and the measured temperatures in the boreholes have been used for calibration. We can see that the temperature in the deepest sediments is calculated to be ~300°C, and the highest temperatures in the wells are 90-150°C.

If we know when the sediments were deposited (formed) and the heat flow, then we can estimate the present-day temperatures in the sediments. If we use the traditional geological time scale, the calculated temperatures of the sediments are shown in Figure 2. We assume that the heat flow has always been the same as today, and we take into account all of the measured temperatures in the wells. As we see, the temperature increases with depth, to more than 300°C in the deepest sediments.

Let us imagine that all of the sediments were deposited some thousands of years ago, as suggested by Whitcomb and Morris. Would it be enough time to warm up the sediments to the temperatures observed in the boreholes? Now we do the same calculations as before, but we assume that all of the sediments were deposited in less than 100,000 years. Figure 3 shows the calculated temperature sediment layers in this scenario. We see that temperature does not exceed 20°C, except for the deepest sediment layers.

Figure 3: Calculated temperature through the sedimentary layers, assuming that the sediments are younger than 100.000 years. All of the other parameters in the calculation are as in Figure 2. The temperatures do not exceed 20 oC in the section, except for the deepest sediments.

Figure 4 shows the calculated temperature profile, assuming that all of the sediments are younger than 1 million years. We see that the temperatures might have exceeded 80°C in the deepest layers, but only 20°C in the wells.

Figure 4: Calculated temperature through the sedimentary layers, assuming that the sediments are younger than 1 million years. All of the other parameters in the calculations are as in Figure 2. The temperatures in the 4 wells do not exceed 20 oC, while they have been measured to between 90 and 150°C.

The temperature is a function of heat flow from the inner of the Earth, but also of the surface temperature and of the thermal properties of the sediments. The thermal properties of the sediments have been measured in laboratories, so they are well known. But what about the heat flow in the past? Heat flow could have been significantly higher in the past; however, probably not very much higher. But let us assume that the heat flow was ten times as high (500 mW/m²) up until 10,000 years ago, compared to present day heat flow (50 mW/m²) in our offshore area. The temperature effect (assuming sediment age less than 100,000 years) is shown in Figure 5; the calculated well temperatures are still not above 10°C, while they are measured at 90–150°C.

Figure 5: Calculated temperature in the sedimentary layers, assuming that the sediments are younger than 100.000 years and the heat flow ten times higher than observed today. All of the other parameters in the calculation are as in Figure 2. The temperatures do not exceed 20 oC in the section, except for the deepest sediments.

Conclusion

We have seen that it is not possible to explain the measured temperature in these sediments on the assumption that the sediments are only some thousands of years old. Using measured properties of the sediments and conventional values for the Earth’s heat flow, we realize that the sediments must be considerably older than 1 million years. Extremely high heat flow cannot help to explain the measured well temperatures, assuming a young sediment age. The calculated temperatures are a function of the surface temperature, which may have been higher in the past. However, this cannot explain why the temperatures in the wells show an increase with depth, and the calculations show that this cannot be achieved over short time span.

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