Tag Archives: geology

Yellowstone volcanism: the three big eruptions

The Yellowstone Supervolcano, fed by a continental hotspot, has erupted many times over its 70 million year history, but three eruptions blanked the continent. Today, the sponge-like upper magma chamber is 80 km by 20 km, or 4,000 km3 by volume, of which 8% is molten; another deeper and larger magma reservoir, 46,000 km3 by volume, of which 2% is molten, lays 65 km beneath the ground. Despite its deceptive beauty, Yellowstone is an active volcano (perhaps most obviously evidenced by its frequent earthquakes) that will violently erupt at some point in the future. Read more

Metamorphic rocks, minerals, grade, and facies

Metamorphic rocks form when a preexisting rock (protolith) is transformed into a different rock due to pressure, heat, or chemical alteration. Tectonics and burial can supply pressure and heat on a wide scale (regional metamorphism), while igneous intrusions can bake adjacent rocks (contact metamorphism). Hydrothermal fluids power chemical alteration. This page has useful diagrams of metamorphic processes, while this one has good notes, and this one has both! Read more

Creatures of the early Paleozoic

This list briefly describes the creatures appeared (and not necessarily when they disappeared, if they did). Keep in mind that all of the creatures listed are marine, and most are soft-bodied invertebrates. Of course, this list doesn't even come close to covering all the Paleozoic creatures, just the ones I found worth mentioning -- if you think I missed one, let me know in the comments! Click on the images to enlarge; hover to see photo credit in alt-text (many are from Nobu Tamura). Read more

Basalt types: tholeiites vs alkali basalts

Essentially, tholeiites are less evolved. They have different normalized rare earth element REE signatures: when normalized by chondrites, the more primitive tholeiites have flatter REE patterns, while calc-alkalis show enrichment in the light REEs (LREE). Tholeiites are associated with oceanic spreading centers (shallow), while alkali basalts are associated with collisional zones (deeper). Read more

Quick facts about the layers of the Earth

Here is an easy chart gathering together basic facts about each of the earth's layers, from top to bottom: the crust, the mantle, and the core. The crust and uppermost part of the mantle (down to 70 km) from the rigid lithosphere, which contains tectonic plates, underneath which lies the fluid taffy-like asthenosphere, which drives plate motion. Unsurprisingly, as you travel deeper into the earth, things get denser, hotter, and and more pressurized.

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Easy Science: how the Appalachian Mountains formed in four steps

The history of the Appalachians spans over a billion years, with four collisions forming the Appalachian Mountains. The last collision occurred around 300 million years ago. Originally, the chain would have rivaled the Himalayas at over 5 km tall, with some mountains perhaps reaching as high as 9 km. Three hundred million years of erosion slowly whittled the mountains away; today, they average 1 km, with the highest point being 2 km at Mount Mitchell, North Carolina. Read more

Did a starburst cause Earth to get buried in kilometers of snow?

Three times before the Cambrian period (545 mya), the entire earth has been buried in several kilometers of snow -- based on evidence including tropical glacial deposits and the cessation of carbonate production (which prefers to form in warmer waters) -- in a phenomenon known as Snowball Earth. But what causes these drastic glaciations to occur? Read more

Most common elements and oxides in rock-forming minerals

After the Big Bang, the universe was made up of the two lightest elements: hydrogen and some helium. Nucleosynthesis was responsible for creating heavier elements; young stars form helium out of hydrogen.

In the later stages of a massive star's life, helium is converted into heavier elements like carbon, oxygen, silicon, and iron. When a star goes supernova, they create elements heavier than iron.  Elements with even atomic numbers are an order of magnitude more common than odd ones. Read more

Easy Science: cross-section of ocean floor geology

The ocean floor forms at seafloor spreading centers, where basaltic magma pushes out through cracks. This magma ultimately comes from the mantle. What would you see if we could punch out a 8 km deep tube from the sea floor? Unfortunately, that isn't yet possible, but thanks to ophiolites, which are parts of the seafloor that have been uplifted to where we can study them, we have an idea of what it would look like. Read more