New answers tagged

1

No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period that had preceded it. If there are no strong elements, some key feature are: flower plants diatoms in the oceans Perhaps the most important of these events, at least for terrestrial life, was the first appearance of the flowering plants, also called the ...


3

Short answer, there isn't one. The J-K boundary does not have a well defined fingerprint or marker, because of this it is in flux with different studies constantly offering to tweek or redefine its date based on their own criteria. https://www.sciencedirect.com/science/article/pii/019566719190001S https://ui.adsabs.harvard.edu/abs/2017EGUGA..1912252L/...


3

To complete the first answer with bigger scale images, here are some pictures of well-known mantle outcrops in Italy and Corsica (figure 4 from Rampone et al. 2020): The caption reads: (a) Centimeter-thick pyroxenite layers embedded in the External Ligurides mantle peridotites (Northern Apennines). (b) Partially dissolved pyroxenite layers (substituted ...


1

"Principles of Igneous and Metamorphic Petrology" by John D. Winter is a good book to get into when you get past the basics and want to learn more about petrology, as it also touches into concepts of density gradients of the earth and the creation of the galaxy. It is pretty pricey so if you found a used one for cheap or a PDF online I would recommend you ...


4

Above the asthenosphere is the lithosphere. The main constituent of the lower lithosphere is peridotite, a coarse-grained igneous rock containing the minerals olivine and pyroxene. Samples of peridotite can be found in the surface. Sections of ocean crust can be uplifted onto continental margins, forming ophiolites (perhaps the best-known example being the ...


5

This is a companion answer to both Erik's and tfb's answers. tfb's answer assumes a uniform density throughout the Earth. This is highly inaccurate. Not to disparage tfb's answer; I've run across physics PhDs who thought that this was the correct model of gravitation inside the Earth. The problem with this model is that the uniform density model is invalid ...


3

I believe Manual of Mineralogy (based on Dana) is a good start for mineralogy and crystallography subjects. It is a good manual to understand the basics behind crystalls and minerals. It is a bit theoric, but it explain crystallography laws you need to know to face microscope. It also list the minerals by groups following Dana classification. I would ...


21

This is a companion to the other answer. The other answer gives values for what the acceleration actually is based on knowledge about the composition of the planet. In this answer I want to introduce some of the mathematical tools that allow you to reason about how gravity varies in and around planets. David Hammen's answer, which I think he wrote ...


52

The below figure, taken from Wikipedia shows a model of the free fall acceleration, i.e., 'gravity'. The left-most point corresponds to the center of the Earth; then further right at $6.3\cdot1000$ km you are at the Earth's surface; and then further out you move into space. You can follow the blue line for PREM to get an idea of the average (expected) ...


0

Pebbles and other mostly non-biological debris are heaped up on the beach by wave action. Then either the sea retreats or the land rises, and these features are left high and dry to become part of the landscape. An example of land rising may be found in Scotland, where relieved of the burden of ice a couple of kilometres thick, the land is still rising more ...


3

The following sources helped me understand these landforms - hopefully they can help you too :) From the Miranda Shorebird Centre: The Miranda-Kaiaua cheniers are first formed as sand and cockle-shell bars on the foreshore or intertidal flats. The bars are then moved landward by wave action. Eventually the bars attain sufficient height to withstand such ...


0

In your question I think you are mixing up metamorphic conditions such as the conditions that gneiss forms from sedimentary rock with the formation of diapirs. Diapirs occur where a less dense layer of a relatively plastic rock has denser overlying formations create sufficient pressure so that the less dense substance deforms and rises over time. Diapirs ...


1

I believe the author's was referring to phenomena like salt diapirs (where mobile salt deposits intrude into heavier overlying sediments). These produce low hills in the gulf coast region of the United States. The salt that is moving is not liquid, it is merely mobile. I do not believe the author of the book you reference was referring to sand and mud ...


2

My understanding of supergene is that it is about mineral enrichment/concentration at the base of an oxidized zone, within a weathered profile. The seasonal/periodic rise and fall of the local water table is critical to supergene enrichment. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ...


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