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Source:Christofferson:Devotional Address:24 Sep 2013:The absence of evidence is not proof
Elder D. Todd Christofferson: "The absence of evidence is not proof. Here’s one small example"
Elder D. Todd Christofferson, "The Prophet Joseph Smith", Devotional Address, BYU Idaho, September 24, 2013:
The absence of evidence is not proof. Here’s one small example. Matthew Roper, in a FairMormon Blog on June 17, 2013, writes about a criticism that was repeated many times over the years about the mention of steel in the Book of Mormon. In 1884, one critic wrote, “Laban’s sword was steel, when it is a notorious fact that the Israelites knew nothing of steel for hundreds of years afterwards. Who, but as ignorant a person as Rigdon, would have perpetuated all these blunders.” More recently Thomas O’Dey, in 1957, stated, “Every commentator on the Book of Mormon has pointed out the many cultural and historical anachronisms, such as steel. A steel sword of Laban in 600 B.C.”
We had no answer to these critics at the time, but, as often happens in these matters, new discoveries in later years shed new light. Roper reports, “it is increasingly apparent that the practice of hardening iron through deliberate carburization, quenching and tempering was well known to the ancient world from which Nephi came “It seems evident” notes one recent authority, “that by the beginning of the tenth century B.C. blacksmiths were intentionally steeling iron.” In 1987, the Ensign reported that archaeologists had unearthed a long steel sword near Jericho dating back to the late 7th century B.C., probably to the reign of King Josiah, who died shortly before Lehi began to prophesy. This sword is now on display at Jerusalem’s Israel Museum, and the museum’s explanatory sign reads in part, “the sword is made of iron hardened into steel.” 
- Elder D. Todd Christofferson, "The Prophet Joseph Smith", Devotional Address, BYU Idaho, September 24, 2013.