RC - Because of the proximity and likeness

[ParthJ26]

Dear Instructors,

Hi.

RC Guide, 6th Edition, Pg 121

Because of the proximity and likeness of Mars to Earth, scientists have long speculated about the possibility of life on Mars. Roughly three centuries ago, astronomers observed Martian polar ice caps, and later scientists discovered other similarities to Earth, including the length of day and axial tilt. But in 1965, photos taken by the Mariner 4 probe revealed a Mars without rivers, oceans, or signs of life. Moreover, in the 1990s, it was discovered that unlike Earth, Mars no longer possessed a substantial global magnetic field, allowing celestial radiation to reach the planet's surface and solar wind to eliminate much of Mars's atmosphere over the course of several billion years.

More recent probes have investigated whether there was once liquid water on Mars. Some scientists believe that the presence of certain geological landforms definitively resolves this question. Others posit that wind erosion or carbon dioxide oceans may be responsible for these formations. Mars rovers Opportunity and Spirit, which landed on Mars in 2004, have both discovered geological evidence of past water activity. These findings substantially bolster claims that there was once life on Mars.

Q4. It can be inferred from the passage that scientists would be more likely to suspect that Mars once held life if there were evidence of each of the following features?

A. Carbon dioxide oceans

B. Celestial radiation and solar wind

C. High daily level of sunlight reaching the planet's surface

D. Volcanic eruptions

E. A significant global magnetic field

My Question:

When I read the question, my interpretation was:

The evidence of which of the following features would make scientists more likely to suspect [or be suspicious of the fact] that Mars once held life?

I thought that if there is that CO2 oceans existed, then those CO2 oceans, rather than water, would have been responsible for the formation of certain geological landforms. CO2 oceans would weaken the evidence of water and in turn, lead scientists to suspect that Mars once held life.

I know it is a silly doubt, but I would really like your thoughts on this one.

Thanks in advance.

Best,

Parth Jain

[Sage Pearce-Higgins]

CO2 oceans would weaken the evidence of water and in turn, lead scientists to suspect that Mars once held life.

I don't get your logic here. Sure, CO2 might explain the landforms and weaken the argument that there was once water, but why would that support the idea that Mars once held life?
Although it's important not to bring too much of your own knowledge to these passages, it's important to know that water is generally seen as one of the necessary conditions for life. This is suggested by the passage: 'Mariner 4 probe revealed a Mars without rivers, oceans, or signs of life.'

[FaysalT485]

Hi Sage,

Regarding answer choice (E).

the passage mentions "...Mars, unlike Earth, no longer possessed a substantial global magnetic field...". The word "no longer" implies that scientist knew that Mars had a Substantial Global Magnetic Field some time ago but it no longer has it.

But the question says "... IF there were evidence of which of the following features?"

What's confusing me is that the evidence (answer E) has already been established in the passage (as i explained above). So how can E be correct ?

[Sage Pearce-Higgins]

What's confusing me is that the evidence (answer E) has already been established in the passage

Sure, we know that Mars doesn't have a substantial magnetic field now, and that a magnetic field - by keeping the atmosphere together - helps fulfill one of the conditions of life. So, as a counterfactual, if Mars had a magnetic field now, then we'd expect it to have a greater chance of having life (now).

You've highlighted what may be a slight weakness in the problem: since Mars used to have a magnetic field, perhaps it's possible that it used to have life. Now, my brain is already beginning to hurt a bit as I think about this one, but I don't think that it's a big deal for the following reasons:
-All the other answer choices are rubbish. Evidence of these things would not help life.
-The magnetic field disappeared a long time ago (four billion years is mentioned in the article).
-The question asks 'if there were evidence'. This could be about the past, but it could just as well be about the present. The Rover could have come back with evidence of a magnetic field present now, meaning that answer E has not been established.

Have faith that thinking hard about problems like this one is good for your neural connections.