Online versions of previously published USGS books are presented exactly as they were printed. However, scientific information often changes before an updated version of a book can be prepared. The USGS intends to provide the interested reader with any updated information that is brought to our attention, whether it be from the author or from a reader.

Dr. Brent Dalrymple, Dean of the College of Oceanic and Atmospheric Sciences at Oregon State University, wrote:

"...there are some errors in [Geologic Time]. The oldest rocks in North America are not the Morton Gneiss but are the Acasta Gneiss Complex near Great Slave Lake -- 4.03 Ga -- and the Isua Supracrustal rocks in West Greenland -- 3.7 to 3.8 Ga. Both are older than the Morton Gneiss. In addition, the best age for the Earth (4.54 Ga) is based on old, presumed single-stage, leads coupled with the Pb ratios in troilite from iron meteorites, specifically the Canyon Diablo meteorite. In addition, mineral grains (zircon) with U-Pb ages of 4.4 Ga have recently been reported from sedimentary rocks in west-central Australia."

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Last updated 12.11.99 (krw)