According to the conclusions of a new research paper, it would seem that oceanic crust forms a lot slower than scientists first calculated, but in a more dynamic manner. Past studies found that as many as 4 cubic miles Details of the investigation appear in the latest issue of the top journal Nature Geoscience. Studies such as this one are important because as many as 60 percent of Earth’s crust lies under the waves, making up the bottom of seas and oceans. Underwater mountain ranges of sorts, called mid-ocean ridges, are the locations through which new oceanic crust is being pushed up from the planetary mantle. The latter is a layer of viscous, molten magma, on which all tectonic plates float.

Plate Tectonics

See Article History Dating, in geology , determining a chronology or calendar of events in the history of Earth , using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques.

These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.

Approximate dating of onlapping reflections on either side of the ridge constrains the timing of its A seismic velocity of m/s for the oceanic crust (on the basis of other areas in the South Atlantic [Sage et al., ; Wilson et al., ] means that the vertical.

Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt—lherzolite interaction. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt—peridotite interaction and subsequent high-pressure metamorphism. These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite.

These observations suggest that melt—peridotite interactions at 80— Ma were induced by partial melting of recycled continental crust. These features imply that the melt—peridotite interactions at 48—64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid. Abundant lower crustal and upper mantle xenoliths exhumed by the Neogene Hannuoba basalts along the northern margin of the North China Craton NCC provide a rare opportunity to study the two types of crust—mantle interaction referred to above Liu et al.

The isotopic characteristics of Mesozoic age lower crustal xenoliths Zhou et al.


For many years, scientists have studied the ocean’s creatures, the effects of introducing chemicals to the water, and the geologic floor of the world’s vast oceans. One creationist believes that the floor of the ocean provides evidence that the earth is much younger than the generally accepted age of 4. This paper will provide an explanation of his claim, as well as evidence and arguments provided by mainstream scientists which causes them to reject this young-earth creationist’s clock.

Before these claims can be considered, a brief explanation of plate tectonics is in order.

The most abundant petrotectonic assemblage preserved in orogens (both collisional and accretionary) is the continental arc, whereas oceanic terranes (arcs, crust, mélange, Large Igneous Provinces, etc.) comprise crust.

It was discovered by submarine crews during WWII when they encountered a vast undersea mountain range while crossing the Atlantic Ocean. Associated with these mountains were deep valleys which, together, dwarfed anything seen on land. After WWII, the ocean floor was surveyed in detail and revealed a very complex topography, unexpected by geologists. Why did this feature occur where it did, and how can it be explained? One interesting discovery was that of linear features or faults that are generally oriented at right angles to the ridges.

They apparently offset sections of the MOR system where the deep valleys occur. Some of these structures are very long, extending almost half the way across the ocean basins. Below is an image showing the age of the oceanic crust in the Atlantic Ocean.

Image Gallery oceanic crust

Because this material makes up the bulk of the down-going portion of the crust consumed into the mantle in subduction zones, which are the loci of the vast majority of the world’s earthquakes and volcanoes, understanding the structure, composition, and evolution of this part of the crustal lithosphere is important for both scientific knowledge and disaster risk analysis.

To learn more about this part of the ocean crust, a major community-driven effort to drill deep bore holes into magmatic rocks on the seafloor by the International Ocean Discovery Program, an effort involving more than 30 scientists from around the world, was carried out in on the Southwest Indian Ridge at a location called the Atlantis Bank. Goals of this research are to determine the size and shape and timing of the intrusive bodies that make up the lower ocean crust, their spatial sequence, and their dimensions.

Samples come from the core drilled on the recent ocean drilling leg. Samples from a previously drilled core in the general vicinity will also be analyzed and compared to those from the new hole to get an idea of the spatial continuity of the igneous intrusive bodies. To accomplish research goals, high-precision Uranium-Lead U-Pb dating of zircons, a mineral resistant to alteration once it is formed, will be used to provide insights into the time and space distribution of magmatism during lower crustal accretion in the ocean basins.

Mid-ocean ridges (MORs) are the prime locations of crustal growth where the upwelling mantle undergoes decompression melting, and continuously supply melts to the ridge systems.

Stumble Upon Advertisement Except perhaps for some remote island dwellers, most people have a natural tendency to view continents as fundamental, permanent and even characteristic features of Earth. One easily forgets that the worlds continental platforms amount only to scattered and isolated masses on a planet that is largely covered by water. But when viewed from space, the correct picture of Earth becomes immediately clear. It is a blue planet. From this perspective it seems quite extraordinary that over its long history Earth could manage to hold a small fraction of its surface always above the sea–enabling, among other things, human evolution to proceed on dry land.

Is the persistence of high-standing continents just fortuitous? How did Earths complicated crust come into existence? Has it been there all the time, like some primeval icing on a planetary cake, or has it evolved through the ages? Such questions had engendered debates that divided scientists for many decades, but the fascinating story of how the terrestrial surface came to take its present form is now essentially resolved.

That understanding shows, remarkably enough, that the conditions required to form the continents of Earth may be unmatched in the rest of the solar system. Earth and Venus, being roughly the same size and distance from the sun, are often regarded as twin planets. So it is natural to wonder how the crust of Venus compares with that of our own world. Although centuries of telescopic observations from Earth could give no insight, beginning in the Magellan space probes orbiting radar penetrated the thick clouds that enshroud Venus and revealed its surface with stunning clarity.

Oceanic crust

See my copyright notice for fair use practices. The Earth’s lithosphere is broken up into chunks called plates with densities around 3. Oceanic crust is only about 6 kilometers thick.

“That feature can only be created by oceanic crust.” But Granot didn’t realize just how old that crust was until he finished processing the data on a hour flight home, Mosher reports.

Lithostratigraphic and biostratigraphic evidence for brief and synchronous Early Mesozoic basalt eruption over the Maghreb Northwest Africa Previously very sparse biostratigraphic data suggested that the Early Mesozoic tholeiitic effusive and intrusive magmatism in the various basins of the Maghreb occurred over a long time Ladinian-Hettangian. However, a detailed comparison of the stratigraphy underlying, interbedded with, and overlying the basalts in these basins shows not only remarkable similarities with each other, but also with sequences in the latest Triassic and earliest Jurassic of eastern North America.

There, the sequences have been shown to be cyclical, controlled by Milankovitch-type climate cycles; the same seems to be true in at least part of the Maghreb. Thus, the Moroccan basins have cyclical sequences surrounding and interbedded with one or two basaltic units. In the Argana and Khemisset basins the Tr-J boundary is identified by palynology to be below the lowest basalt, and the remarkably close lithological similarity between the pre-basalt sequence in the other Moroccan basins and to the North American basins – especially the Fundy basin – suggests a tight correlation in time.

Likewise, the strata above the lowest basalt in Morocco show a similar pattern to what is seen above the lowest basalt formation in eastern North America, as do the overlying sequences.

oceanic crust

Both continental and oceanic crust make the uppermost part of the earth. There are different strata of the earth that are formed by different materials of different density and physical properties. Among the most crucial properties of these layers is their density.

Oceanic Crust The crust that forms the ocean basins. It is basaltic in composition, and comprises an upper layer of pillow lavas, a middle zone of vertical dolerite dykes and a lower layer of gabbro. It is basaltic in composition, and comprises an upper layer of pillow lavas, a middle zone of vertical dolerite dykes and a lower layer of gabbro.

Accurate method to date oceanic crust TheallIneed. Cheadle, UW associate professor of geology and geophysics, says the UW team has unlocked the door to the 60 percent of Earth’s surface covered by water. U-Pb dating of zircon is widely regarded as the best technique for providing the absolute age of rocks on land, according to Barbara E. John, the paper’s second author and professor of geology and geophysics.

The zircon dating technique has been used extensively to answer fundamental questions such as when and how fast the Earth’s continental crust forms. Until now, scientists have relied on geophysical methods based on magnetism to date oceanic crust. Because the field flips through time from normal to reversed polarity, the rocks record the polarity, creating alternating stripes on either side of a mid-ocean ridge.

But this method cannot reveal all the complexity involved in the growth of ocean crust,” John says. Cheadle says one of the reasons zircon dating hasn’t been conducted previously is because some scientists believed that rocks in ocean crust don’t contain zircon. After collecting their samples, the scientists used a Sensitive High Resolution Ion Micro Probe to determine the absolute ages of 17 samples from Atlantis Bank about 75 miles south of the Southwest Indian Ridge in the southern Indian Ocean.

Using the U-Pb zircon dating method, they found they could determine the absolute age of oceanic crust with an error of less than 1 percent of the age. The dating was conducted at the U. Furthermore, the scientists discovered that 25 percent of the samples they dated are up to 2. This site is no longer updated.

Magnetic Reversals and Sea Floor Spreading

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