How many years can a mountain exist? Bob Dylan’s rhetoric question has just received yet another scientifically-based answer. Researchers from Wageningen University & Research (WUR) and Denmark’s Technical University (DTU) have developed a new method that can measure the exposure duration of rocks and sediments, leading to new insights in landscape evolution. In Scientific Reports (Nature) of this week they reveal their innovative technique.
The interactions of sunlight with plants and animals is common knowledge that begs no special introduction. However, fewer of us realise that sunlight interacts with rocks too, involving subtle subatomic processes that are generally difficult to observe. In a rock initially shielded from light, the defects within its crystals fill with electric charge over time, as a result of the surrounding environmental and cosmic radiation. When this rock is then exposed to sunlight, some of the trapped charge immediately at the surface will recombine and emit photons, in a process called ‘luminescence’.
Light empties trapped charges
As sunlight exposure continues, deeper and deeper regions within the rock will subsequently interact with the incoming sunlight and get similarly emptied of trapped charge. The transition zone between the rock’s surface where no trapped charge exists, and deeper regions where electron traps are fully occupied, is called the ‘luminescence bleaching depth’. This depth can provide geoscientists with vital information regarding the precise timing of landscape formation, bedrock erosion rates, sediment transport distances, sky cover conditions, and so on. Read more