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One of the classic early papers demonstrating that biostratigraphic age of basal sediments does in fact increase with distance from ridge axes in a manner consistent with sea-floor spreading was that of Maxwell et al. These authors examined 7 complete sediment cores taken along a transect across the south Atlantic, 5 on the west of the Mid Atlantic Ridge, and 2 on the east of the MAR. Extension of the astronomically calibrated (polarity) time scale to the Miocene/Pliocene boundary. Their biostratigraphic analyses showed clearly that the "a foraminiferal zone. (1970) also attempted to estimate the rate of seafloor spreading, by using the (at the time) newly available K-Ar absolute ages for the paleontological zones.

(1990) reported estimates of plate velocities from SLR measurements taken from 1978-1988 from 22 tracking stations distributed on North Americas, Eurasian, African, Australian, Pacific, Nazcan, and South American plates. Late Neogene chronology: new perspectives in high-resolution stratigraphy.

In short, astronomical dating is based on the correlation of sedimentary cycles, or cycles in various paleoclimate proxies (such as 18O/16O ratios in foraminifera tests), with cyclic variations of the earth's orbital geometry.

The periods of the Milankovitch cycles are computed to be 19-23ka for precession or 'wobble,' 41ka for obliquity or 'tilt,' and 100ka for eccentricity (Cronin, 1999).

The dates of magnetic reversals derived from both methods, although agreeing well with each other, are consistently 5% or so older than dates derived earlier from earlier K-Ar dates.

For instance, the date of the Bruhnes/Matuyama boundary was estimated at 0.73Ma by K-Ar, but 0.78 by both astronomical and 40Ar/39Ar (Biostratigraphic evidence can be used to test sea-floor spreading.

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