Did the K-T impactor look like this?
    A slice of the Pueblito de Allende carbonaceous chondrite (Type CV3). Vertical dimension = 37 mm. Photo by author (use prohibited)


    Dr. Frank Kyte of UCLA, who disovered the meteorite fragment in the K-T boundary sediments from the Pacific Ocean (Kerr, 1996; Kyte, 1998), believes that the impactor that carved-out the Chicxulub crater in the Yucutan Peninsula of Mexico was of the chondritic type. A chondrite (pronounced "KAHN-drite") is a class of stoney meteorite that is more primitive both in it's composition and in it's structure than are the other types of stoney meteorites. Chrondrite meteorites are very distinctive in appearance. The most common variety (called "ordinary chondrites") are composed of small BB-sized spherules (chondrules) of the minerals olivene and enstatite, all embedded in a fine-grained dark groundmass of rock and nickel-iron metal. In the much rarer "carbonaceous chondrites", the interstitial nickel-iron metal is usually absent, and white-colored blobs (called "calcium- and aluminum-rich inclusions", or "CAI" for short) are scattered throughout the rock. These light-colored blobs can be seen in the photo above. Inside the CAIs, scientists have discovered material that may pre-date the formation of our solar system, itself! CAIs are therefore the oldest matter in the solar system that scientists have access to. The photo above is of a slice from the Pueblito de Allende meteorite (a carbonaceous chondrite) that fell in Mexico on Feb. 8, 1969, so it is NOT the fossil meteorite fragment discussed in Kyte's paper. But if the impactor was a chondritic asteroid, it may have had an internal appearance similar to the Allende meteorite.

    Here is what Kyte (1998) said of the meteorite fragment that was found in the K-T boundary layer:

    "The fossil meteorite from DSDP Hole 576 appears to be from (1) a chondritic meteorite with (2) significant amounts of metal and sulphide (4-8%), (3) large inclusions [larger than 200 um] of mafic minerals that also contained metal, and (4) 30-60% fine-grained matrix. The known meteorite groups that best fit these criteria could be the CV, CO, and CR carbonaceous chondrites."

    REFERENCES

    1. Kerr, R.A. 1996. A piece of the dinosaur killer found? Science 271:1806.

    2. Kyte, F.T. 1998. A meteorite from the Cretaceous/Tertiary boundary. Nature 396: 237-239.

    3. Kyte F.T., J.A. Bostwick, and L. Zhou. 1994. The KT boundary of the Pacific plate, pp. 64-65, in New developments regarding the KT event and other catastrophes in Earth history, (Abstract). Lunar Planet. Inst. Cont. No. 825.

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