The answer is, in the 1.5 billion years since its intrusion, erosion in the landscape by rivers and other agents, such as glacial ice, has worn away the surrounding rocks.
(The answer; is; in the 1.5 billion years since its intrusion) Context(The answer is,List([0, 13))):(erosion in the landscape by rivers and other agents, such as glacial ice; has worn away; the surrounding rocks)
The answer is,List([0, 13))
The answer erosion in the landscape by rivers and other agents, such as glacial ice
is has worn away
in the 1.5 billion years since its intrusion
the surrounding rocks