Passage Summary: Scientists found tiny 4.2-billion-year-old diamonds in Australia that are part of the Earth's original outer shell. This helps prove how quickly that shell formed after the planet was born.

Reasoning: Microdiamonds found in Australia are 4.2 billion years old and are fragments of the Earth's early crust, which formed only 300 million years after the Earth itself.

Analysis: This set of facts establishes a timeline for the early Earth. If the microdiamonds are fragments of the crust and they are 4.2 billion years old, then the crust must have existed at least 4.2 billion years ago. Since the Earth formed 4.5 billion years ago (300 million years prior to the diamonds), we can conclude that the crust formed within that first 300-million-year window. The correct answer will likely be a simple chronological deduction based on these numbers.