Default product listing sorting

Hi there
On shop page on the product listing on top right I disabled the sorting, so it sorts as default.
But I dont know it does sorting according to what default?
Date? or price or what?
since my web site no purchase catalogue site, I prefer that it does sorting according to the date. First older published products then newer. My question is:
1-As default what is the sorting?
2-If it does according to published date, and older first on top then newer ones, its ok by me, if not how can I do that? (I disabled the user to select sorting option)
thank you