prinits wrote:
The axis of Earth’s daily rotation is tilted with respect to the plane of its orbit at an angle of roughly 23 degrees. That angle can be kept fairly stable only by the gravitational influence of Earth’s large, nearby Moon. Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life. Mars, for example, has only very small moons, tilts at wildly fluctuating angles, and cannot support life.
If the statements above are true, which one of the following must also be true on the basis of them?
(A) If Mars had a sufficiently large nearby moon, Mars would be able to support life.
(B) If Earth’s Moon were to leave Earth’s orbit, Earth’s climate would be unable to support life.
(C) Any planet with a stable, moderate axis tilt can support life.
(D) Gravitational influences other than moons have little or no effect on the magnitude of the tilt angle of either Earth’s or Mars’s axis.
(E) No planet that has more than one moon can support life.
The axis of Earth’s daily rotation is tilted with respect to the plane of its orbit at an angle of roughly 23 degrees. Axis of Earth is tilted at roughly 23 degrees
That angle can be kept fairly stable only by the gravitational influence of Earth’s large, nearby Moon.Only a large, nearby moon has the ability to keep the angle fairly stable.
Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life. Without this moderate tilt (23 degrees) which is stable, planet's climate is too extreme to support life.
Mars, for example, has only very small moons, tilts at wildly fluctuating angles, and cannot support life. Mars, which has small moons, tilts at wildly fluctuating angles (so the angle is neither moderate nor stable). It cannot support life.
What must be true?
(A) If Mars had a sufficiently large nearby moon, Mars would be able to support life.
No. If Mars had a sufficiently large Moon nearby, it might have been able to keep the angle stable. Would the angle be moderate? We don't know. Would Mars have had a million other things needed to support life? We don't know.
The statement is a hypothetical conditional. If A were true, B would have happened.
But we cannot say that B would have happened.
(B) If Earth’s Moon were to leave Earth’s orbit, Earth’s climate would be unable to support life.
Correct. We are given that only a large nearby moon can keep the angle stable. Without this moderate, stable tilt, Earth's climate would not be able to support life. If the Moon were not there, the angle would not be stable and hence no life.
(C) Any planet with a stable, moderate axis tilt can support life.
Not correct. We need a million other things to go right too. A stable, moderate axis tilt is necessary, not sufficient.
(D) Gravitational influences other than moons have little or no effect on the magnitude of the tilt angle of either Earth’s or Mars’s axis.
We don't know what has effect on the magnitude of the tilt angle. We just know that Moon is able to keep the angle stable.
(E) No planet that has more than one moon can support life.
Not given.
Answer (B)