UPDATED: December 16, 2013, at 11:52 p.m.

Shortly after 9 a.m. Monday, the roughly one third of students in the introductory chemistry and biology course Life Sciences 1a who were sitting for their final exam in Emerson Hall were greeted by the shrill ringing of a fire alarm heralding a campus bomb scare.

As those students were evacuated, the remaining two thirds of the class, divided between Geological Lecture Hall and Yenching Auditorium, began taking their exams, blissfully unaware of the disruption in and around Harvard Yard until they were notified of the threats by course staff approximately midway through their exams.

After unconfirmed bomb threats prompted law enforcement to evacuate four campus buildings Monday morning, several of the morning and afternoon’s final exams—including the Emerson Hall sitting of LS1a—were cancelled and rescheduled as course staff and administrators adjusted to the day’s events.

Courses with final exams scheduled for 9 a.m. Monday in the three affected classroom buildings—the Science Center and Emerson and Sever Halls—were cancelled, with grading and rescheduling options varying for each course.

Students in some courses with morning exams, including Government 1510: "American Constitutional Law” and Life and Physical Sciences A: “Foundational Chemistry and Biology,” had the option of taking the exam at a rescheduled time this week or at the start of next semester, or not taking the exam at all and accepting their current grade. For its part, LS1a required students in the evacuated Emerson Hall exam sitting to make up their missed exams Monday evening or in early spring.

Most exams scheduled for 2 p.m. proceeded as scheduled—with several exceptions. Three afternoon exams scheduled to be held in the Science Center were cancelled, and two mathematics exams were relocated. And students who felt unprepared to take their still-scheduled afternoon exams were excused from the sitting and given the choice of accepting their current grade without the final exam or changing their course grading status to pass/fail with no penalty.

Some students already stressed by exams were unsettled by Monday’s events and its implications for their academics. The news about the bomb scare “rattled a lot of people,” said Philip J. Abboud ’17, a student in LS1a who took the exam in the Geological Lecture Hall.