EAE2252 - Topic 2 - 2 Flashcards
<p><strong><span>What are Geochronologic units?</span></strong></p>
<p>2 points.</p>
<ul><li>Divisions of time distinguished on the basis of the rock record expressed by chronostratigraphic units </li><li>Viz. the interval of time during which sand flows in an hourglass</li></ul>
<p><span>EAE2522 3aa</span></p>
<p><strong><span>What are Chronostratigraphic units?</span></strong></p>
<p>2 points.</p>
<ul><li>Tangible bodies of rock selected by geologists to serve as reference sections for all rock units formed in the same period of time. </li><li>Viz. the amount of sand that flows through an hourglass during a certain period of time</li></ul>
<p><span>EAE2522 3ab</span></p>
<p><strong><span>What are Periods?</span></strong></p>
<p>3 points.</p>
<ul><li>The basic units of geological time </li><li>Commonly used when referring to Earth history </li><li>The chronostratigraphic term "system" is used for rocks deposited in this time (e.g., Jurassic System)</li></ul>
<p><span>EAE2522 3ac</span></p>
<p><strong><span>What are Epochs?</span></strong></p>
<p>3 points.</p>
<ul> <li>The major divisions of periods: some have names, for example the Llandovery, Wenlock, Ludlow in the Silurian</li> <li>Others are simply Early, (Mid-) and Late divisions of the period (e.g. Early Cretaceous and Late Cretaceous).</li> <li>The chronostratigraphic equivalent is the "series", but it is important to note that the terms Lower, Middle and Upper are used instead of Early, Middle and Late.</li></ul>
<p><span>EAE2522 3ad</span></p>
<p><strong><span>What are Ages?</span></strong></p>
<p>3 points.</p>
<ul> <li>The smallest commonly used divisions of geological time are ages, and the chronostratigraphic equivalent is the "stage."</li> <li>They are typically a few million years in duration.</li> <li>For example, the Early Cretaceous Epoch is divided into 6 Ages (e.g., the Wonthaggi Fm is of Aptian age and it belongs to the Aptian Stage of the Early Cretaceous Series of rocks).</li></ul>
<p><span>EAE2522 3ae</span></p>
<p><strong><span>What are Chrons?</span></strong></p>
<div>Are short periods of time that are determined from <em>palaeomagnetic information</em>, but these units do not have widespread usage outside of <em>magnetostratigraphy</em></div>
<p><span>EAE2522 3af</span></p>
<p><strong><span>Global Standard Section and Point</span></strong></p>
<p>5 points.</p>
<ul><li>An internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. </li><li>Most, but not all, GSSPs are based on paleontological changes - usually described in terms of transitions between different faunal stages </li><li>As of 2020, 74 of the 104 stages that need a GSSP have a ratified GSSP. </li><li>Usually marked by a "golden spike" hammered into the "type section" </li><li>All other beds of similar age around the world are then correlated with the strata that contain the 'golden spike', correlation (lithostratigraphy, biostratigraphy, magnetostratigraphy, etc.).</li></ul>
<p><span>EAE2522 3ag</span></p>
<p><strong><span>Mass Extinctions</span></strong></p>
<p>6 points.</p>
<ul><li>Many of the boundaries between </li><li>Periods and Eras are marked by </li><li>Mass Extinction events </li><li>An extinction event is a widespread and rapid decrease in (mostly marine) biodiversity on Earth. Such events are identified by a sharp change in the diversity and abundance of multicellular organisms. </li><li>They occur when the rate of extinction increases with respect to the rate of speciation. </li><li>The largest extinction even is at the Permian-Triassic (P-T) boundary</li></ul>
<p><span>EAE2522 3ah</span></p>
