in/at

Or leave them both out.

The nomads lived by hunting and fishing during the last Ice Age which began about 35,000 BC and ended about 10,000 BC.

A sidenote: the use of BCE Before Current/Common Era has become more common here in the US.

Joe(not without arguments)Nation

Hi Joe

The accident happened at about noon.
The accident happened about noon.

I see both the above sentences in print. Isn't it similar to the question I posted.

Use "in" for specific, known years. To use it for such a thing as the start of an Ice Age is to pretend to an accuracy you cannot achieve.

Napoléon Bonaparte was born in [the year] 1769, and died in [the year] 1821.

If you cannot be precise, because you personally do not know the exact year, or because you are making a general remark, or (as in the case of prehistory) it is unknowable, just use "around".

Motor cars became practical around 1890.

The Iron Age began around 1200 BC in the part of the world which later became India.

Fred, who knows little history, thinks that Queen Victoria died around 1900. (She actually died on the 22nd of January, 1901.)

Hi.

Contrex just explained it very well.

Joe('in about' pulls both ways, 'in'(specific) about (non-specific))Nation

Thanks, Contrex and Joe.

The same thing applies, I assert, to hours of the clock, except that we use "at". "At about" is to be avoided!

I saw Joe around 10 o'clock. (imprecise)

I saw Joe at 10:05 on Monday November 26th in the year 2007.

Thanks, Contrex.