#19 - Paleontologist: It is widely, but falsely, held that

[PresidentLSAT]

So D, is soil not from land? Where else would the soil the stimulus is talking about be from?

Also, C, visually, if those rocks by the beach are half submerged like most rocks at beaches, how is it enough justification for life on land? It's not like the rocks are scattered elsewhere far from the ocean. Most rocks are not fully in, and it barely has anything to do with land activity

[Adam Tyson]

The author is trying to support the claim that life on land is older - maybe much older - than just half a billion years. Life on land might have begun as far back as 1.2 billion years ago, and the evidence is that rocks that old have carbon 14 in them, and carbon 14 is a byproduct of life.

Answer D weakens the argument by saying that the carbon 14 in those rocks could have come directly from the atmosphere, rather than being extracted from the atmosphere by plants and microbes and then released into the soil when those things died.

Consider this analogy: I smell cigarette smoke in my house. That usually happens when my daughter hangs out with her friends, who all smoke a lot, and it gets into her hair and clothes, and then she comes home and brings that smell with her. So I conclude that she has been hanging out with her smoking friends. But what if, instead, someone was standing out on the sidewalk in front of my house, smoking, and the smoke just wafted in through an open window? That would weaken my conclusion that my daughter was hanging out with her friends while they smoked.

Answer D is doing the same thing here. The author thinks the carbon 14 in the rocks was deposited there by life forms. But if instead it just came straight from the atmosphere, without being extracted and deposited by life forms, then there's no reason to believe there were any life forms at the time.

"Soil" isn't the issue here. The issue is "directly from the atmosphere."