How long ago were diamonds delivered to the earth's surface?

Diamonds are believed to have formed deep within the Earth's mantle over a span of billions of years through geological processes involving high pressure and temperature. The timing of their delivery to the Earth's surface, primarily through volcanic eruptions that brought them up in kimberlite and lamproite pipes, is estimated to have occurred around 20 million years ago. This makes the choice of 20 million years ago the most accurate answer among the given options. Understanding the geological timeline helps provide insight into the natural processes involved in the formation and transportation of diamonds, illustrating the connection between diamonds and Earth's geological history. This is a significant aspect of the study of diamonds and their origins.