The sentence given is an example of a comma splice. A comma cannot join together two independent clauses. The two clauses can be made into two separate sentences, or can be joined using a semicolon instead of a comma. 

Two independent clauses being joined only by a single comma result in an error known as the "comma splice." In the example above, a period, a comma and a conjunction, or a semicolon would all be appropriate to punctuate the sentence.

When two independent clauses are joined only by a single comma, this results in an error known as the "comma splice." Since both of the clauses in the example above are independent, they could stand on their own as full, grammatically complete sentences, a semicolon, period, or comma and a conjunction would be needed to properly punctuate the sentences (or compound sentence).

The example sentence attempts to create a compound sentence using only a comma, thus creating a comma splice. In the example above, something more than a comma is needed to separate the two clauses. 

This list is punctuated correctly. There should be a comma between each item in the list and an additional comma on either side of “Susanna,” which modifies “their sister.” (If “their sister, Susanna,” was the first or second item in the list, a semicolon would be needed to separate the items for clarity’s sake, but here it’s unnecessary.) In the second half of the sentence, a semicolon correctly separates the two independent clauses without a conjunction.

Here we have a comma splice: two independent clauses that are incorrectly separated by a comma. Two independent clauses in the same sentence must be punctuated by either a comma with a conjunction or a semicolon. Correctly punctuated, this sentence would read: “Although certainly the best known of the early aviators, Orville and Wilbur Wright were not the only inventors pioneering airplane designs; the Montgolfier brothers should also be remembered for their timely rediscovery of the hot-air balloon.” The comma after “aviators” is correct, since it’s separating an independent from a dependent clause.

Here we have a comma splice: the first two independent clauses in this sentence are incorrectly separated by a comma. (The latter two of the three independent clauses are correctly punctuated with a comma and a conjunction word.) Multiple independent clauses in the same sentence must be punctuated by either a comma with a conjunction or a semicolon. Accurately punctuated, the sentence should appear as follows: “The inhabitants of Ulan Bator inhabit a unique cultural juxtaposition; they are in a cosmopolitan city with a population of more than 1 million residents, but they are also influenced by a nomadic heritage.” 

Here we have a comma splice: two independent clauses that are incorrectly separated by a comma. Two independent clauses in the same sentence must be punctuated by either a comma with a conjunction or a semicolon. Correctly punctuated, this sentence would read: “Contrary to popular belief, the artisanal cheese-makers did not live a decadent, gourmet lifestyle; they had to scrimp and save on their personal grocery expenditures in order to keep their business afloat.” Elsewhere, commas are correctly separating two adjectives in a list and an independent clause from a dependent clause.

Here we have a comma splice: two independent clauses that are incorrectly separated by a comma and should instead be punctuated by either a comma with a conjunction or a semicolon. Written correctly, this sentence would read: “Lee has always been a proponent of tighter gun regulations; he believes countries that enforce strict firearms laws are generally more peaceful, safe, and open-minded than those that don’t.” At the end of the sentence, commas are appearing correctly to punctuate the list.

Here we have a comma splice: two independent clauses that are incorrectly separated by a comma and should instead be punctuated by either a comma with a conjunction or a semicolon. Written correctly, this sentence would read: “A rigorous national curriculum should encompass not only excellent preparation in reading and mathematics but also so-called extracurricular activities such as sports, arts, and music; studies have shown that the most successful people in life are often those with divergent, varied interests.” “The list “sports, arts, and music” is correctly punctuated with commas, as are the two adjectives that precede “interests.”