Which of the following situations is a typical starting point for primary ecological succession?

Introduction / Context:
This question is from ecology. Succession describes how biological communities develop over time in a particular area. Primary succession and secondary succession differ in whether soil and previous life are present at the start. Identifying a correct starting condition for primary succession is a common exam task.

Given Data / Assumptions:
- The focus is on primary succession. - Options describe different types of disturbed or exposed land. - Primary succession starts where there is no soil and almost no pre existing life.

Concept / Approach:
Primary succession occurs in areas where living organisms have not previously existed or where any earlier community has been removed so completely that soil has not yet formed. Examples include newly formed volcanic rock, bare rock exposed by retreating glaciers, or newly formed sand dunes. Secondary succession, by contrast, occurs where soil already exists, such as in abandoned farmland or neglected yards.

Step-by-Step Solution:
1. A neglected yard still has soil, seeds, and existing organisms, so it fits secondary succession. 2. An abandoned city has soils, seeds, and often many remaining plants and animals. 3. Abandoned farmland has well developed soil and seed banks, again leading to secondary succession. 4. A surface exposed by a retreating glacier is bare rock or freshly exposed substrate with little or no soil. 5. Such a bare surface is a classic example of a primary succession starting point. 6. Therefore, the correct answer is a surface exposed by a retreating glacier.

Verification / Alternative check:
Ecology textbooks often use retreating glaciers as textbook illustrations of primary succession, showing the gradual colonization by lichens, mosses, grasses, shrubs, and trees over long periods.

Why Other Options Are Wrong:
Neglected yard: Already has soil, plants, insects, and microbes, so succession here is secondary. Abandoned city: Concrete and buildings may be present, but underlying soil and life remain in many places. Abandoned farmland: Contains soil and seed banks, leading to secondary succession.

Common Pitfalls:
Students may mistakenly think that any disturbed land represents primary succession. The key is to check whether soil and previous life are present. If soil already exists, the process is secondary succession, not primary.

Final Answer:
A typical starting point for primary succession is a surface exposed by a retreating glacier.