The action that describes an experimental investigation is (D) Measuring the temperatures at which two rock samples melt.
An experimental investigation involves conducting a controlled experiment to gather data and test a hypothesis. In this case, measuring the temperatures at which two rock samples melt involves manipulating variables (temperature) and collecting data to analyze the relationship between the independent variable (temperature) and the dependent variable (melting point).
This action allows for the comparison and analysis of the behavior of the two rock samples under different temperatures, providing valuable insights into their properties. By measuring the melting points, scientists can make observations and draw conclusions about the composition and characteristics of the rock samples.
On the other hand, options (A), (B), and (C) involve other scientific processes, such as exploration, description, and comparison, but they do not specifically involve an experimental investigation. They may be observational or descriptive in nature, rather than involving manipulation and control of variables to gather quantitative data.
Therefore, the action that best describes an experimental investigation is (D) Measuring the temperatures at which two rock samples melt.