Question

If a typical rate for the accumulation of sediments is \(1 \mathrm{~mm} /\) year, what thickness (meters) of sedimentary rock could accumulate over a period of 30 million years?

Short answer

The thickness of sedimentary rock that could accumulate over a period of 30 million years, given a typical accumulation rate of 1mm/year, is 30,000 meters.

Step-by-step solution

Convert time to years

We are given a time period of 30 million years, which we need to express in terms of years. 30 million years = 30,000,000 years

Calculate the accumulated thickness in millimeters

We know that the accumulation rate is 1mm per year. To find the total accumulated thickness over 30,000,000 years, we simply multiply the accumulation rate by the number of years. Total accumulated thickness (in millimeters) = Accumulation rate × Number of years Total accumulated thickness (mm) = 1mm/year × 30,000,000 years Total accumulated thickness (mm) = 30,000,000 mm

Convert the accumulated thickness to meters

Since we need to express the final result in meters, we need to convert the accumulated thickness from millimeters to meters. We know that 1 meter = 1000 millimeters, so we can use that to convert the accumulated thickness to meters. Total accumulated thickness (m) = Total accumulated thickness (mm) / 1000 Total accumulated thickness (m) = 30,000,000 mm / 1000 Total accumulated thickness (m) = 30,000 m The thickness of sedimentary rock that could accumulate over a period of 30 million years is 30,000 meters.

Key concepts

Geological Time

To truly appreciate the scale of geological changes, we must first understand 'geological time'. It's the time frame over which Earth's geological history is analyzed and comprises millions or even billions of years. Unlike human history's frequent events, geological changes often occur over vast periods of time, which can be difficult to conceptualize.

For instance, the 30 million years mentioned in our sedimentation problem is just a fraction of Earth's 4.5-billion-year history. This time scale allows us to observe the slow and cumulative processes, like sedimentation, that can build great mountain ranges, carve out canyons, and lay down vast sedimentary rock formations. Geological time provides context for the slow pace at which these changes can occur and highlights the persistent and often imperceptible accumulation of geological effects over eons.

Sediment Accumulation Rate

The 'sediment accumulation rate' is central to understanding how sedimentary rock layers form over time. This rate indicates how quickly sediments—tiny particles of rock and organic material—collect in a given area. Rates can vary depending on environmental factors such as location, climate, and nearby geological activity.

For the exercise, the given rate was 1 millimeter per year, which might seem negligible until considered over geological time. When calculating the sediment accumulation, students must remember that this slow rate, consistent over millions of years, leads to substantive accumulation, like in our example where sediments could form a 30,000-meter thick deposit over 30 million years. This concept is crucial for interpreting Earth's stratigraphic record, as each layer of sedimentary rock represents a snapshot of Earth's past environment.

Earth Science Calculations

In 'earth science calculations', numerical methods are used to quantify natural processes, allowing scientists and students alike to understand and predict how Earth's systems behave over time. The calculations often require unit conversions and working with large numbers, typical for geological studies.

The step-by-step solution illustrates the importance of unit conversion by switching from millimeters to meters to express the sediment thickness in a more comprehensible unit. Furthermore, the ability to perform such calculations helps us to quantify Earth's dynamic processes and to make those large timescales and rates manageable and meaningful. As you progress in Earth sciences, you'll find that mastering these calculations arms you with the tools to decode the planet's history and forecast its future changes.