Question

The absolute ages of the following 5 units have been determined radiometrically (units A and F) or by fossil evidence (units M, Y, and X). Use this information to answer following questions.

Unit A: 2.8 billion years old
(= 2800 million years old)

Unit M: 600 million years old

Unit Y: 270 million years old
Unit F: 120 million years old
Unit X: 40 million years old


1.) If we want to estimate how much geologic time is missing along the unconformity marked as #1. What are the two rock units essential to solve this question?



Following Q2 using the absolute ages of these two essential rock units to calculate the missing time recorded at the unconformity 1 (an event of erosion and/or non-deposition):

Missing time: __ million years

Answer 1

The missing time recorded at unconformity #1 is 560 million years.

How did we get the value?

To estimate how much geologic time is missing along unconformity #1, you'll need to identify the two rock units that are essential for this question. The key information for this is the concept of unconformities, which represent gaps in the geologic record due to erosion or non-deposition.

In this case, you can look for the youngest rock unit below unconformity #1 and the oldest rock unit above it. The unconformity represents a period of time where either erosion occurred or no new sediments were deposited.

Based on the ages provided:

1. The youngest rock unit below unconformity #1 is Unit X (40 million years old).

2. The oldest rock unit above unconformity #1 is Unit M (600 million years old).

So, the two essential rock units for estimating the missing time along unconformity #1 are Unit X and Unit M.

Now, to calculate the missing time, you subtract the age of the younger unit from the age of the older unit:

`\[ \text{Missing time} = \text{Age of Unit M} - \text{Age of Unit X} \]`

`\[ \text{Missing time} = 600 \, \text{million years} - 40 \, \text{million years} \]`

`\[ \text{Missing time} = 560 \, \text{million years} \]`

Therefore, the missing time recorded at unconformity #1 is 560 million years.