Sublithospheric diamonds: Plate tectonics from Earth's deepest samples (Annual Reviews, 2024)
✦ A transparent, white, octahedral, rough, lithospheric diamond from South Africa contained in its brown to black kimberlite matrix. This cover photo for the Winter 2013 issue of Gems and Gemology (v. 49, pp. 188-222) highlights the article, Recent advances in understanding the geology of diamonds by Steven Shirey and James Shigley http://dx.doi.org/10.5741/GEMS.49.4.188 (VRL# 157869). Photo by Robert Weldon. © 2014 Gemological Institute of America).
✦ This is a vertical slice of the mantle under Japan and Korea from the original study (Li, C., Hilst, R., Engdahl, E., Burdick, S. (2008). A new global model for P wave speed variations in Earth's mantle. Geochemistry, Geophysics, Geosystems). Colder mantle with faster P wave travel times is shown in blue colors, warmer mantle with slower travel times is shown in red colors. Superdeep diamonds form in association with (Modified from an original figure by Josh Wood, Deep Carbon Observatory).
✦ Pink and grey banded gneisses from Point Lake, NWT, Canada —the oldest rocks studied in the Central Slave Basement Complex. Such obvious intermixing of contrasting rock types is one of the challenges in studying some of the oldest rocks on Earth. Rocks such as these are hallmarks of the oldest continental crust on Earth and are a direct record of what the Earth was like almost 4 billion years ago. (Photo: Jesse Reimink).
✦ The ages of the rocks on Earth's surface are displayed in this map from the United States Geological Survey (USGS). The age of continental rocks is as follows: older than 2.5 billion years old in orange; 2.5 to 1.6 billion years old in pink, 1.6 to 1.0 billion years old in green, 1.0 to 0.54 billion years old in purple and younger than 0.54 billion years old in blue and yellow. The ocean floor is in shades of blue and is less than 0.2 billion years old. The important thing to note is the pattern of the age distribution; the oldest rocks are at the center of the continents and the youngest are at the edges.