The most common and most likely answer to this crossword clue is the 10 letter word GEOLOGICAL
I've seen this crossword clue in The Times
G
E
O
L
O
G
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Buddy explains!
The straight part
We know that "in terms of earth science" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in terms of earth science = geological.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GEOLOGICAL mean?
GEOLOGICAL adjective- Of, or relating to geology or a geologic time scale.