The field of geological oceanography owes much to American ______ Marie Tharp, a pioneering oceanographic cartographer whose detailed topographical ma...

Sentence Structure

• The field of geological oceanography
• owes much to American geologist[?] Marie Tharp,
  • a pioneering oceanographic cartographer
    • whose detailed topographical maps of the ocean floor and its multiple rift valleys
      • helped garner acceptance for the theories of plate tectonics and continental drift.
• Where [?] = comma OR nothing OR semicolon OR colon

Understanding the Meaning

Let's start reading from the beginning:

The field of geological oceanography owes much to American geologist...

This is where we have the blank. Let's look at the choices:

• Choice A: geologist,
• Choice B: geologist
• Choice C: geologist;
• Choice D: geologist:

So we're deciding what punctuation (if any) should follow "geologist." To see what works here, let's read the rest of the sentence and understand what it's saying!

The sentence continues: "American geologist ____ Marie Tharp, a pioneering oceanographic cartographer whose detailed topographical maps of the ocean floor and its multiple rift valleys helped garner acceptance for the theories of plate tectonics and continental drift."

Now let's understand what this is telling us:

• "Marie Tharp"
  • is a proper name - the specific name of the geologist being discussed
• "a pioneering oceanographic cartographer"
  • is additional descriptive information about Marie Tharp
  • tells us what made her important
• "whose detailed topographical maps..."
  • describes her specific contribution
  • these maps helped prove plate tectonics theory

So the complete picture is:

• The sentence is saying the field owes much to one specific person - Marie Tharp, who was an American geologist
• It then adds more details about who she was and what she did

What do we notice about the structure here?

• We have a pattern: general description + specific name
  • "American geologist" is the general category
  • "Marie Tharp" is the specific name that identifies which geologist
• The name "Marie Tharp" is essential information
  • It tells us WHICH geologist we're talking about
  • Without it, we wouldn't know who the sentence is about
  • It's not just extra information - it's the identification
• When a proper name directly identifies which person you're referring to, it's essential identification and needs NO punctuation before it

Compare these two patterns:

• "American geologist Marie Tharp" - the name identifies which geologist
• "Marie Tharp, an American geologist" - the description adds info about Marie

In our sentence, the name comes after the description, so we need:
"American geologist Marie Tharp" (no punctuation between them)

So we need Choice B - no punctuation

Grammar Concept Applied

Essential vs. Additional Information: When NOT to Use Commas

When a proper name directly identifies which specific person or thing a general noun refers to, that name is essential information (called restrictive or essential modification in grammar terms). Essential information is not set off by commas.

The key distinction:

Pattern 1: General noun + Specific name = NO comma (name is essential identification)

• "American geologist Marie Tharp made important discoveries"
  • "Marie Tharp" identifies which geologist
  • Without it, we don't know who
• "President Lincoln delivered the Gettysburg Address"
  • "Lincoln" identifies which president
  • Essential to the meaning

Pattern 2: Name + General description = YES comma (description is additional info)

• "Marie Tharp, an American geologist, made important discoveries"
  • We already know who (Marie Tharp)
  • "an American geologist" adds extra information
  • Could remove it and sentence still identifies the person

How this applies to our question:

• "American geologist Marie Tharp" follows Pattern 1
• The name "Marie Tharp" is essential - it tells us which geologist
• Therefore, no comma is needed between "geologist" and "Marie Tharp"