Early Earth is thought to have been characterized by a stagnant lid tectonic regime, in which the upper lithosphere (the...
GMAT Information and Ideas : (Ideas) Questions
Early Earth is thought to have been characterized by a stagnant lid tectonic regime, in which the upper lithosphere (the outer rocky layer) was essentially immobile and there was no interaction between the lithosphere and the underlying mantle. Researchers investigated the timing of the transition from a stagnant lid regime to a tectonic plate regime, in which the lithosphere is fractured into dynamic plates that in turn allow lithospheric and mantle material to mix. Examining chemical data from lithospheric and mantle-derived rocks ranging from 285 million to 3.8 billion years old, the researchers dated the transition to 3.2 billion years ago.
Which finding, if true, would most directly support the researchers' conclusion?
Step 1: Decode and Map the Passage
Part A: Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "Early Earth is thought to have been characterized by a stagnant lid tectonic regime, in which the upper lithosphere (the outer rocky layer) was essentially immobile and there was no interaction between the lithosphere and the underlying mantle." |
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| "Researchers investigated the timing of the transition from a stagnant lid regime to a tectonic plate regime, in which the lithosphere is fractured into dynamic plates that in turn allow lithospheric and mantle material to mix." |
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| "Examining chemical data from lithospheric and mantle-derived rocks ranging from 285 million to 3.8 billion years old, the researchers dated the transition to 3.2 billion years ago." |
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Main Point: Researchers used chemical analysis of ancient rocks to determine that Earth transitioned from a stagnant lid tectonic regime to a plate tectonic regime 3.2 billion years ago.
Step 2: Interpret the Question Precisely
What's being asked? Which finding would most directly support the researchers' conclusion about the timing of the transition.
What type of answer do we need? Evidence that would strengthen or validate their conclusion that the transition occurred 3.2 billion years ago.
Any limiting keywords? "Most directly support" means we need the strongest, most relevant evidence for their specific conclusion.
Step 3: Prethink the Answer
- The researchers concluded that Earth transitioned from a stagnant lid regime (no lithosphere-mantle interaction) to a plate regime (lithosphere-mantle mixing) 3.2 billion years ago
- For evidence to support this conclusion, we need something that shows evidence of mixing between lithospheric and mantle materials occurring around 3.2 billion years ago, when it wasn't happening before
- Discusses proportions of rock types before and after 3.2 billion years but doesn't address whether materials from these sources were mixing
- Proportions alone don't indicate interaction between the two sources
- Focuses on compositional diversity within each rock type but doesn't show mixing between lithospheric and mantle materials
- Shows correlation between rock types increasing at 3.2 billion years, but correlation doesn't directly prove the mixing that defines the plate regime
- Shows mantle-derived rocks younger than 3.2 billion years contain material from lithospheric rocks
- This directly demonstrates the mixing between lithospheric and mantle materials that characterizes the plate regime, with timing that matches exactly when the researchers say the transition occurred