6000 years age of earth.
The church isn't necessarily young earth. It is however young life, in specific human life. Doctrinally the spirt of life in animals and plants is only 6000 years old. The church doesn't explore what this means to the fossil record, dendrochronology and other related science facts.
The ramifications of young life is still anti-science and problematical for doctrine. Now it's mostly inferences from other statements and scriptures. They want deniability. If you have seminary stuff from the 70s and 80s, then it can be pretty clearly shown. Doctrine is what you teach. Seminary material is therefore doctrinal. You won't find refutation of this earlier teaching, but it hasn't been taught that way for some decades now giving contemporary members more wiggle room. You can find claims that the Church doesn't teach a Young Earth, and this is contemporaneously true.
Still, there are some doctrinal sources.
https://www.lds.org/scriptures/bible-chron?lang=eng
This strictly sources Adam, not necessarily the age of the earth. Archaeology is a strong challenge to this claim, Gobekli Tepe especially so
There is a lot of religious handwaving around related issues, but more on that later.
See also the various imagery from the past for seminary and so on in chronology.
https://www.google.com/search?q=lds+bib ... 95&bih=971
Scripturally, the two big guns are DC 77, which spells out a literal 7000 year timeline of man/earth of 1000 years per dispensation. Apologists will say this is figurative, but that' requires some serious re-interpretation of the contents of that section. Or they'll argue that the earth could be older, this is only when human time keeping started. It really doesn't support the apologist position. The lesson manual for this section is pretty vague too. They are desparate for wiggle room.
The other is 2 Nephi 22:2 (and a bit surrounding that. This plainly declares no death before the fall. This shoots holes in lots of apologist theories. They'll argue that it only means spiritual death. Or that that applies to the Garden of Eden and not the earth. Or only to when souls entered into human evolution. There is plenty of doctrine that without the spirit, it isn't alive. This is the whole argument about abortion, "we don't know when the spirit enters the baby so we err on the side of caution". See also 77 where it declares that all life has spirits. The hair splitting necessary to argue against this scripture usually defeats any other doctrinal claim you want to apply it too to point out how weak the arguments are.
The way 2Ne22 talks about the creation and the fall pretty plainly indicates it means everything everywhere. Apologists will argue this reflects only what the Nephites believed, not necessarily what is factual doctrine. However, that's a two edged sword as it can be applied to any statement in the BoM, plus it's the most correct book on earth etc.
Similarly Moses 6:48 and more weakly 1Cor15:22
https://www.lds.org/ensign/1980/09/the- ... e?lang=eng is a refutation of modern science essentially. It argues that our science is based on only local phenomena and things could be different elsewhere. Could is the operational word here. This is about weakly justifying faith through feelings as the supreme epistemology. Of course, feelings let any non-evidence based claim be equally as true and valid.
You may hear a Talmadge quote about the altar at Adam Ondi Aman, that there is fossiliferous rock in that altar so it means that life predated Adam. To me that indicates Talmadge recognized the issues, but he never constructed and taught a specific timeline of the earth and man that I know of. Rather, this topic has been left alone.
Other analyses:
http://www.lds-mormon.com/6000.shtml
http://www.mormonthink.com/scienceweb.htm#age
satire with an interesting quote that itself is authentic
http://stakepresident.blogspot.com/2011 ... earth.html
You can readily find apologetic material on Fair and from Jeff Lindsay and others.