If you're attracted to (A), you might be reading it as "fossils don't have biomarkers," which would undercut the idea that fossilized life could be the source of the biomarkers in petroleum. But that's not what (A) says. It just says there have been fossils without biomarkers. In other words, some fossils don't have biomarkers. But plenty of other fossils could still have biomarkers, and those fossils could be the source of the biomarkers we find in petroleum.

If you're attracted to (B), you might be assuming that petroleum had to form around the time the earth was formed. If that were true, then the fact that living organisms came along much later would suggest the petroleum couldn't have come from life. But the stimulus never says petroleum formed at or near the time of the earth's formation. That's what the deep carbon deposits date to, not the petroleum itself.

Petroleum could have formed long after the earth's formation, well after living organisms emerged. Maybe organisms lived, died, became fossils, and then the petroleum formed from those remains. (B) doesn't create any timeline conflict with the geologist's reasoning.

Even if it takes many millions of years for organisms to become petroleum, that doesn't make it unlikely. The earth is billions of years old. There's been plenty of time for organisms to live, die, and slowly transform into petroleum over millions of years. If you're attracted to (C), you might be assuming that petroleum had to form quickly, but nothing in the stimulus requires that assumption.

This provides an alternate explanation for how biomarkers could have ended up in petroleum. The geologist assumed the biomarkers in petroleum are there because the petroleum formed from living things. But (D) offers a different possibility: bacteria thrive deep inside the earth's crust, which is where the deep carbon deposits are located. If living bacteria are present in the same area where petroleum forms from deep carbon deposits, those bacteria might be the source of the biomarkers.

Remember, biomarkers indicate the past or present existence of a living organism. The geologist treated the biomarkers as evidence of petroleum's ancient biological origin. But (D) suggests the biomarkers might reflect the present existence of bacteria living alongside the petroleum, not the origin of the petroleum itself. Petroleum could have formed from deep carbon deposits and still contain biomarkers, because the bacteria living nearby might have contributed those markers.

(D) doesn't prove the geologist is wrong. It doesn't establish that petroleum definitely came from deep carbon deposits. But it doesn't have to. It just needs to show that the geologist's evidence (biomarkers in petroleum) doesn't guarantee her conclusion (the deep-carbon-deposit theory is wrong). By providing a plausible alternate source for the biomarkers, (D) weakens the argument.

Pay close attention to which carbon deposits the scientists are talking about. The scientists' theory involves deep carbon deposits dating from the formation of the earth. These deposits have been around since the earth formed, which means they existed before any living thing did. (E) describes carbon deposits that were formed from fossilized remains of plants. But plants are living things that came along well after the earth's formation. So the carbon deposits in (E) are a completely different kind of deposit than the ones the scientists are talking about.

Even if some carbon deposits out there were formed from plants, those aren't the deposits at issue in this argument. The geologist is responding to a theory about carbon deposits that predate life entirely. (E) has no impact on that debate.