To study centuries-old earthquakes and the geologic faults that caused them, seismologists usually dig trenches along visible fault lines, looking for sediments that show evidence of having shifted. ███
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What is the author's primary ███████ ██ █████████ ██ ███ ████ ██ ██████ ██ █ █████ ████████ ██████ ███████
to emphasize the ████████ ████ █████ ██████ ████████ ███ █████████ ██████████ ██ █████ ███████ ████ ████████
The author doesn’t emphasize the speed of lichen growth; the growth is simply presented to help us understand how measuring lichen growth can help date an earthquake.
to offer an ███████ ██ █ ██████ ███████ ████ ███ ██ ███ ███████ █████ █████ ██ ██████
We don’t know whether the lichen mentioned has one of the slowest known rates of growth.
to present additional ████████ ██████████ ███ █████ ████ █████████████ ██████████ ███ █████ ████████ ████ ██ ██████
The author hasn’t introduced the idea that environmental conditions can alter lichen growth rates. That idea comes in P3 and is not related to the purpose of the line we’re asked about.
to explain why ████████████ █████ ████ ███ ██████ ███████████ ████ ████████ ██ ███ ████ ███ █████
The claim that lichenometry works best for earthquakes in the last 500 years is in P3 and isn’t related to the purpose of the line we’re asked about.
to provide a █████ ██ ███ ████ ██ █████████ ██ █████ ██████ ██████ ██████
This is the best answer. Not exactly what we anticipated, but no other answer makes any sense. The author mentions the growth rate to give us a sense of the lichen growth rate, which helps us understand how measuring lichen growth rate can date an earthquake.