Part 1: Engage (Anchoring Phenomenon)

The Phenomenon: Approximately 27.5% of Puerto Rico’s surface is covered by a limestone region known as the karst belt. This area features spectacular landforms, including mogotes (hummocks), extensive underground cave systems (like the Río Camuy Caves), and deep sinkholes (dolines). These massive, solid rock formations have been hollowed out and reshaped over time, demonstrating a powerful connection between the properties of water and its effects on Earth materials and surface processes.

Observe and Wonder:

1. How could water—a seemingly gentle liquid—carve massive caves out of solid rock?
2. What properties of water might allow it to interact chemically with Earth materials?
3. Generate two “need to know” questions about how water interacts with bedrock to create these formations.

   • ---

   • ---

Part 2: Explore (Simulation Investigation)

Estimated Time: 45-60 minutes

Materials:

• Computer or tablet with internet access
• Interactive Simulation: Puerto Rican Karst Topography
• Calculator (optional)

Procedure: In this investigation, you will test how different environmental variables affect the rate of chemical weathering in limestone bedrock over thousands of years.

Part A: The Baseline System

1. Open the simulation and set all controls to their default values:
   • Annual Rainfall: 1500 mm
   • Rainwater Acidity (pH): 5.6 (Normal)
   • Limestone Fractures: Medium (3)
2. Press Play and observe the simulation for 1000 simulated years.
3. Pause the simulation and record the following data in your baseline table:
   • % Dissolved Limestone: _____
   • Aquifer Volume: _____

Part B: Testing Variables You will now systematically change one variable at a time to determine its effect on the rate of dissolution. For each test, click “Reset” before changing the variable. Run each test for 1000 simulated years.

Part 3: Explain (Sensemaking)

Using the data you collected from the simulation, answer the following questions to make sense of the phenomenon.

1. Chemical Effects of Water: How did increasing the acidity (lowering the pH) of the water affect the rate of limestone dissolution compared to the baseline? What property of water makes it an effective solvent for chemical weathering? _____
2. Mechanical and Structural Factors: How did the number of pre-existing fractures in the limestone affect the formation of caves and sinkholes? Explain why the surface area exposed to water is an important factor in this process. _____
3. Volume and Transport: What effect did increasing the annual rainfall have on the aquifer volume and the total amount of limestone dissolved? Why is the continuous flow of water necessary for the sustained chemical weathering of rock? _____

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

The Deliverable: Construct a scientific explanation to answer the following prompt: How do the chemical properties of water and the physical structure of bedrock interact to create the karst topography of Puerto Rico?

Your explanation must include:

• A claim that directly answers the prompt.
• Evidence from your simulation data (Part 2), specifically referencing the effects of acidity (pH), rainfall volume, and rock fractures.
• Reasoning that connects your evidence to the scientific principles of chemical weathering, the polarity of the water molecule, and how water acts as a solvent to break down and transport Earth materials.

Draft your explanation here: _____

Part 5: Extension Options

• Local Geology: Research the geology of your local region. Are there any karst formations or areas prone to sinkholes near you?
• Climate Change Connection: How might global climate change (which can alter both average rainfall amounts and ocean/rainwater acidity) affect the future formation of karst topography in regions like Puerto Rico?

Teacher Notes (HS-ESS2-5 Alignment)

This task aligns with the Next Generation Science Standards (NGSS) Performance Expectation HS-ESS2-5: Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

• Science and Engineering Practice (SEP): Planning and Carrying Out Investigations - Students conduct a simulated investigation, altering variables (rainfall, pH, fractures) to produce data that serves as evidence for how water affects Earth materials.
• Disciplinary Core Idea (DCI): ESS2.C: The Roles of Water in Earth’s Surface Processes - Students investigate water’s exceptional capacity to dissolve and transport materials (limestone/calcium carbonate) through chemical weathering.
• Crosscutting Concept (CCC): Structure and Function - Students infer how the physical structure of the rock (fractures) and the chemical properties of water (acidity, solvent capabilities) function together to create karst landforms.

Evidence Statement Alignment: Student work demonstrates the following observable features:

• 1a: Students describe the phenomenon under investigation, which includes a connection between the properties of water (acidity, volume) and its effects on Earth materials (limestone dissolution).
• 2a(iv): Students collect data on the chemical effects of water on Earth materials (the solubility of limestone in water of varying pH) to infer chemical weathering.
• 4a: Students collect and record measurements (e.g., % Dissolved Limestone, Aquifer Volume) indicating the predicted effect of water’s properties on Earth’s surface.