Relative Age Determination Research Articles

Technique for rapid determination of relative ages of lunar areas from orbital photography

Development of a technique for determining relative ages of regions of the lunar surface from orbital photography using a model of small-impact erosion. The erosion model relates the shape of a crater to the integrated flux of debris that has impacted the surface since that crater was fresh. The shape of the most modified crater of a particular diameter is thereby related to the relative age of the surface. Application of this analysis to orbital photography reveals that the major mare units vary in the accumulation of impacts by more than a factor of 3. Comparison of these data with crystallization ages determined from samples collected during the Apollo 11 and 12 missions indicates that the impact fluxes were decreasing during the stages of mare formation. An exponentially decaying flux for the last 3.5 b.y. with a half-life of 0.6 to 1.4 b.y. is compatible with the data.

Recent advances in human evolutionary studies.

In recent years there has been important progress in the study of man's origins and evolution and in the development of man's capacity for culturally patterned behavior. These advances have been the result of developments in relative and absolute age determination of fossil hominid remains and the sediments that contain them; in the recovery of hominid skeletal remains that fill significant gaps in the fossil record and often provide new and unsuspected evidence of the morphology and functional structure fo the early Hominidae; and in the discovery, controlled excavation, and detailed evaluation of contexts, associations, and residues of early hominid occupation places. The nature and probable significance of these discoveries are critically evaluated, especially with respect to ongoing and future research problems of paleoanthropology.

The African elephant, Loxodonta africana:a field method for the estimation of age

The need for a field method of determining and describing the relative age of African elephants collected in their natural habitat arose during a recent research project, and has led to an attempt to formulate a laminary age standard for use in the field, based upon direct observations and measurements on the lower right molars. For this purpose aseries of 31 African elephants of both sexes, covering almostthe complete potential age range of an elephant's life, and of known body condition, locality and size, has been used as the basis for constructing a reference chart of molar laminary age. Eye lens weights were also obtained for 26 of these specimens, but, although indicativeof a direct correlation with laminary age, they were obtained in insufficient numbers to provide an adequate sequence. Each of the specimens used was first observed alive, then shot and examined post mortem during the course of a research project*on cardiovascular disease, in which the determination of relative age formed an integral part.

Palaeomagnetic Dating of some Younger Dikes in Southern Norway

THE occurrence of several localities of younger basic dikes in southern Norway has aroused considerable geological interest in the past. The dikes are especially common in the coastal districts between the Permian Oslo graben and the schists of the Stavanger area. Their absolute age has remained unknown, but a connexion with the Permian igneous activity in the Oslo area has been proposed1,2. Nevertheless, radioactive dating of younger Norwegian dikes has hitherto not been carried out. On this background a systematic palaeomagnetic study of the younger dikes in Norway has been undertaken by me, assuming it to be a useful tool for absolute as well as relative age determinations. So far only the extensive swarms of dolorites in the anorthosite rock complex in Rogaland have been investigated and in this communication the results are summarized.

Determination of Relative Ages of Lunar Craters by Albedo and Polarization Measurements

ONE of the most important tasks in selenology is to establish the relative ages of different parts of the lunar crust. It may be argued that, during the lifetime of a crater, its floor would be darkened at a uniform rate by the destructive effects of ultra-violet light on the rock crystals. The empirical relationship : may be fitted to the albedo (ρ) measurements of Markov and Fedorets1, where Δ is the diameter of a crater in kilometres.

The Stratigraphic Panorama

Stratigraphy means literally the descriptive science of strata. It deals with the composition, form, arrangement, distribution, succession, and classification of rock strata and it also involves the interpretation of these features in terms of mode of origin, environment, age, history, relation to organic evolution, and relation to other geologic concepts. Stratigraphy concerns itself with the complete picture of the rocks of the earth9s crust as strata of various kinds and the significance of these strata in the earth9s geological development. There are many branches of stratigraphy, depending on the particular features of rock strata under consideration. One of the most important is chronostratigraphy which deals with the age determination and age classification of strata. Its basic purpose is to interpret the history of the earth through the chronologic sequence of its rock strata. The principal means used to work out chronostratigraphy are (1) the physical interrelations of strata, (2) the relation of strata to sequence of organic evolution, and (3) radioactivity age determinations. Valuable supplementary evidence of age or chronostratigraphic position can be supplied by other features of rock strata and other geologic phenomena such as lithology, mineralogy, ore deposits, chemical composition, paleomagnetism, paleoclimatology, changes in sea level, orogeny, igneous activity, and unconformities. However, few of these can be proved to have had effects which were distinctly recognizable, identical in character, and synchronous over the whole world. Coordinated utilization of all possible lines of relative and absolute age determination and time correlation offers the best promise for continued progress in chronostratigraphy. Joined to the problem of the dating of strata and the establishment of their sequence with respect to earth history is the task of chronostratigraphic classification. The record of 4 thousand million years, written in millions of cubic miles of strata, is too vast to be comprehended as a whole and it is necessary to break it down into smaller more practicable units. The only adequate reference standards for the scope of these chronostratigraphic units are specifically designated intervals of rock strata—stratotypes. The fundamental unit of world-wide chronostratigraphic classification is the system. The systems, largely established in Western Europe during the first half of the last century, were originally thought to constitute “natural” units with respect to earth history. In view of the local and rather haphazard manner in which most of them originated and the primitive state of world geological knowledge at that time, it is difficult now to see them as “natural” divisions of world-wide extent. Nevertheless the belief is still supported by many, including the USSR Stratigraphic Commission, that the systems are marked off by a concurrence of major events in geologic history and major changes in the course of organic evolution. They assume that all lines of Stratigraphic evidence converge to form “natural” divisions of strata with respect to time and that hence separate kinds of Stratigraphic classification—lithostratigraphic, biostratigraphic, etc.—are unnecessary. On the other hand, investigations by other competent workers of the evidence for world-wide “natural breaks” in either the diastrophic record or the record of organic evolution have resulted in strong judgments to the contrary. The conclusion seems reasonable, regardless of what may be proved eventually, that it has not yet been demonstrated that world-wide “natural breaks” in the general character and continuity of strata exist at the scale of the presently accepted geologic systems nor that the evidence at the boundaries of the present systems is such as to allow them to be considered as the “natural” world-wide division points of the chronostratigraphic scale. Rather, the evidence suggests that our geologic systems are only arbitrary chronostratigraphic units in a continuum characterized by intricately overlapping and not necessarily coincident changes in the many and various properties and attributes of rock strata and that their principal significance is that of standard units of chronostratigraphic reference, independent of other kinds of Stratigraphic classification. Regardless of opinion on the relation of these units to events of earth history, the critically important point is that the systems and their major subdivisions should be tied down by international agreement to specifically designated and delimited sequences of rock strata—stratotypes—so as to provide a uniform basis of definition for everyone.

VOLCANIC GEOLOGY OF TOOWA VALLEY, SOUTHERN SIERRA NEVADA, CALIFORNIA

Toowa Valley, a broad east-west late mature valley astride the Sierra Nevada west of Olancha, California, contains flows and cones composed of olivine basalts, scorias and agglomerates in a volcanic field miles long, including 4 eruptive centers, one of which is hitherto unreported. Each center shows several flow phases followed by cone building, breaching, and later partial reconstruction. Volcanic domes in and near Toowa Valley are also described. Contact relations of flows of Toowa volcanism, swamp sediments of meadows of pre-volcanic origin, volcanic domes of an adjacent area, and recognized physiographic surfaces of the Sierra Nevada, allow relative age determinations of several heretofore undated events.