Copper Discovery and Human Evolution
The discovery of copper marks a significant milestone in human history, particularly during the Chalcolithic period.

Understanding the Chalcolithic Period
- The Chalcolithic period, also known as the Copper Age, spans approximately from 4500 to 3500 BCE.
- It was characterized by the use of copper tools alongside stone tools, indicating a transition in technology and lifestyle.

Technological Advancements
- The ability to extract and manipulate copper represented a leap in human ingenuity.
- Early humans discovered that copper could be found in its native form, which made it easier to work with than other metals.

Societal Implications
- The introduction of copper tools improved agricultural practices, enhancing food production.
- This advancement led to the growth of settled communities and the development of trade networks.

Comparison with Other Periods
- In contrast, the Paleolithic period (Old Stone Age) primarily involved the use of stone tools.
- The Mesolithic period (Middle Stone Age) showcased a transition but did not prominently feature metal use.
- The Neolithic period (New Stone Age) saw advancements in farming but still relied on stone tools until the advent of copper.

Conclusion
The correct answer to the question is option 'D' - Chalcolithic man discovered copper, marking a transformative phase in human history that paved the way for further technological and societal advancements. This period laid the groundwork for the subsequent development of metallurgy and civilization as we know it today.