Let's begin by understanding the age of the Earth based on scientific consensus. Earth is estimated to have formed about 4.54 billion years ago.
To determine the correct answer among the options, let's break down each choice:
A. 5 million years ago
- This option suggests Earth formed relatively recently in geological time. However, we have strong evidence from geological studies and radiometric age dating that Earth's formation is much older than 5 million years.
B. 50 million years ago
- Although much longer than 5 million years, 50 million years is still vastly shorter than the actual age of the Earth. The Earth is far older than 50 million years, as indicated by geological and fossil records.
C. 50 billion years ago
- This option is too far in the opposite direction. The age of the universe itself is estimated to be about 13.8 billion years, which means it's impossible for the Earth to be 50 billion years old.
D. 5 billion years ago
- This option is the closest approximation to the scientifically accepted age of the Earth, which is about 4.54 billion years. Therefore, rounding this value to 5 billion years is reasonable for the purposes of our multiple-choice question.
Given these analyses, the most accurate answer is:
D. 5 billion
Thus, the correct completion to the sentence "Earth formed about ___ years ago" would be:
Earth formed about 5 billion years ago.
