Geologic Time & Dating Rocks Without Isotopes (Biostratigraphy & Lithostratigraphy) | GEO GIRL

In this video, we go over how the geologic timescale was originally built. The modern geologic time scale has numerical ages associated with each time period, but originally we used fossils to construct the timescale. The use of fossils to date and correlate rocks globally is called biostratigraphy. Biostratigraphy is still very relevent today because we cannot use radiometric dating on all rock types. For most sedimentary rocks, we have to use their fossil content to figure out their age. I talk about the general principles behind relative dating of rocks (dating rocks relative to one another rather than using radiometric techniques) and how biostratigraphy works, specifically the use and characteristics of index fossils, in this video. We then go over how we can correlate rocks using other metrics, like rock type (lithology) and magnetic signature. The use of lithology to correlate rocks is called lithostratigraphy, and the use of magnetic signature to correlate rocks is called magnetostratigraphy. We can now go over and check out stratigraphic correlations and ages using radiometric ages of the rocks to correlate them and make sure it matches what we determined without radiometric dating. This use of rock ages for correlation is called chronostratigraphy. All of these stratigraphic techniques help us piece together everything that has happened through earth's history and when it all happened. I give an example at the end of the video of how we can use stratigraphy to find periods of sea level rise and fall in the rock record (trangsessive and regressive sequences). Hope you enjoy! ;)

References: Earth System History: https://amzn.to/3v1Iy0G

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0:00 Video Outline
0:57 Geologic Timescale Overview
2:54 True Scale of Geologic Time
3:39 Absolute vs Relative Dating
4:53 Relative Dating Principles
7:54 Ordering Geologic Events (Practice)
10:35 How The Geologic Time Scale was Made
12:07 Extinction Events Define Period Boundaries
14:11 Stratigraphy & Correlation
15:19 Index Fossils for Biostratigraphy
17:40 Index Fossil Examples
19:24 Is Biostratigraphy Still Used?
21:16 Magnetostratigraphy
22:53 Lithostratigraphy
23:31 Strat Columns & Cross Sections
25:08 Transgressive & Regressive Sequences
26:47 Unconformities

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