Learn English – Why use “the” in “than the 3.5bn years ago”


Why has the been used before 3.5bn in the sentence below? Doesn't the sentence make sense without the the?

Researchers hope rocks collected here will confirm that volcanic activity on the Moon continued until far more recently than the 3.5bn years ago that is the estimate derived from studies of currently available samples.

Source: https://www.economist.com/science-and-technology/2020/11/21/china-plans-to-bring-back-the-first-moon-rocks-for-40-years

Best Answer

The reason for "the" is that this refers to a particular 3.5 bn year limit, i.e. the specific one that was mentioned in the previous research.

You may object that there aren't distinct 3.5 bn years ago eras - there can only be one. Logically that is true but sometimes usage overrides logic.

So we could say

  1. 3.5 billion years ago, there was volcanic activity on the Moon.

  2. 3.5 billion years ago, the first signs of life appeared on Earth.

These are independent statements so we could talk about "the 3.5 billion years ago that there was volcanic activity" and "the 3.5 billion years ago that there was life on Earth".

The reason we can refer to them in this way might be because they are both estimates and one might be a much more accurate estimate than the other, so they are in some way distinct.