#elatina

Then the Earth Melted

Between 800 and 650 million years ago, there is evidence in the geologic record for 2 large glaciations on Earth. There are large chunks of debris in sediments that look like material carried by ice to the oceans, and piles of sediment that look like those found where glaciers end. These glaciations are thought to have been extreme; there is evidence that the glaciers picked up sediments that could only have formed in tropical settings. That means the glaciers might have reached the equator and froze over the planet completely; a state known as Snowball Earth (https://tmblr.co/Zyv2Js2F9u82R).

Geologists have hypothesized that the breakup of a Snowball Earth event involves a huge greenhouse effect. Even if the planet’s surface is frozen for millions of years, volcanoes still spit out CO2 and CO2 is a greenhouse gas. Eventually, so much CO2 gets into the atmosphere that it overwhelms the cooling effect of the ice and the ice suddenly collapses. That CO2 winds up in a carbonate deposit found on top of the snowball layers in many areas around the world (https://tmblr.co/Zyv2Js2SJnwt7).

Some scientists have found evidence that they suggest is inconsistent with the proposal that the whole planet froze over, and suggest instead that the glaciations were smaller. So other researchers continue to hunt for outcrops of rock that record different parts of the snowball earth sequence; these rocks are one of them.

These are sedimentary rocks from the bottom of the Elatina formation in South Australia. This rock sequence contains 27 meters of rippled sediments. Scientists can use the size and spacing of ripples to estimate the depth of the water that the grains were deposited in. New research published by scientists at Colorado College, Caltech, and Texas A&M characterized the ripples throughout these 27 meters of sediment and found that all of it was deposited in less than 10 meters of water and in less than 100 years.

Doing a quick bit of math – for these ripples to form in shallow water even though the unit is 27 meters thick, during the time period represented by this unit, water levels at this site rose by more than 15 meters. This rapid rate of sea level rise is consistent with the rapid glacier collapse that is expected at the end of a snowball Earth event – huge releases of water, huge motions of sediment, and huge increases in sea level over rapid times. These sea level increases are 100x faster than those occurring today.

-JBB

Image credit and original paper: https://bit.ly/2Hltsek

 Letné želatína recepty a tipy

V lete nič nehovorí o dobrom staromódnom želatínovom zákusku.

Ako dieťa si pamätám svoju babičku a veľkú tetu, ktoré spolu súťažia, aby som zistil, kto by mohol prísť s najlepším dezertom pre naše každoročné letné rodinné pikniky. Musím priznať, že moja veľká teta zvyčajne vyhrala! Myslím, že želatínové dezerty sú teraz rovnako populárne, ako vtedy. S takou rozmanitosťou receptov, ktoré sú…

The Elatina diamictite

This rock comes from the Elatina formation and is found in Flinders Ranges National Park in South Australia, and contains an Australian dollar for scale.

The Elatina formation is mostly made up of sandstones, but occasionally contains this lithology as well, a rock type called a diamictite. That term specifically refers to a rock made up of 2 distinct grain sizes (very coarse grains surrounded by much finer-grained material) but generally is used to describe rocks that are deposited by glaciers.

Glaciers can carry chunks of variably-sized rocks along with them and deposit those rocks in finer-grained sediments, like those found on the ocean floor or on lake bottoms, so true diamictites are common results of glaciation.

This rock comes from a very interesting time period, about 650 million years ago from a period generally known as the Cryogenian. Glacial deposits are found in many locations around the globe in rocks from this time, including in areas that may have been close to the equator. This diamictite therefore could be one of the remnants of a “Snowball Earth” event, a proposed time when glaciers grew so much that they either covered much of the Earth or in fact closed off entirely at the Equator.

Much research continues today into units like this one to try to uncover the extent and timing of these planetary-scale glacial events.

-JBB

Image credit: Wikipedia commons: http://commons.wikimedia.org/wiki/File:Elatina_Fm_diamictite.JPG