The most common and most likely answer to this crossword clue is the 10 letter word QUATERNARY
I've seen this crossword clue in Independent
Q
U
A
T
E
R
N
A
R
Y
More clues leading to the result QUATERNARY
Buddy explains!
The straight part
We know that "according to geologists nowadays" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case according to geologists nowadays = quaternary.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 QUATERNARY mean?
QUATERNARY noun- A quaternary compound.
- The Quaternary period or the system of deposits laid down during it.
- Of fourth rank or order
- Of a mathematical expression containing e.g. x4
- Relating to or in number base four
- Quaternary ammonium
- Composed of four elements