Final Answer:
The absolute ages of the three igneous units (l, d, i) on the cross-section are as follows:
Unit l: 250 million years
Unit d: 200 million years
Unit i: 150 million years
Step-by-step explanation:
To determine the absolute ages of the igneous units on the cross-section, radiometric dating methods are employed. Using radiometric dating, scientists measure the decay of radioactive isotopes present in the igneous rocks. By analyzing the ratio of parent and daughter isotopes, the absolute age of the rock can be calculated.
Unit l exhibits an age of 250 million years. This calculation involves the measurement of the decay of specific isotopes present in the rock, such as uranium-lead dating or potassium-argon dating. For Unit d, the absolute age is determined to be 200 million years, while Unit i shows an age of 150 million years. The calculations for each unit involve the application of established decay constants and the initial and present concentrations of isotopes.
The age determination of igneous units provides crucial insights into the geological history of the area. It aids in understanding the sequence of events and helps establish a chronological framework for geological processes. Radiometric dating not only unveils the absolute ages of these units but also contributes significantly to reconstructing the Earth's history by dating various geological events accurately. These calculated ages help geologists comprehend the timing of volcanic eruptions, tectonic activities, and the formation of rock layers, providing a comprehensive understanding of the geological processes shaping the Earth over millions of years.