Earth's Biography: Reading the Rocks

• Lecture is about creating Earth's biography by learning to read the rocks.
• The key question is how to tell the history of the Earth with no observers.

Course Introduction

• Most students may not have prior geology instruction.
• It's necessary to become familiar with geology's rules.
• This is to understand dinosaurs, their ages, environments, and behaviors.
• Knowledge of Earth's dynamics aids understanding of environmental variables.
• These variables acted as pressures, impacting dinosaur and other life evolution.

Determining Earth's History

• The lecture explores origins of stratigraphy in telling relative time.
• Stratigraphy involves drawing layers to determine age relations among rocks.
• Bio/stratigraphy uses fossil evidence to draw layers, determining age relations among rocks.

Rock Layers

• Outcrops of rock can be described and sketched.
• Rocks from the bottom can be described as pinkish and massive.
• Pinkish rocks can be finely layered or bedded.
• Light-colored rocks can lack layering and are massive.
• Vertical lines on rocks is due to blasting the outcrop, not the rocks formation.
• Some rocks can be light colored and have light dips.
• Consider a rock as a book with signs indicating its history.
• "Reading" the book requites the language in which it is written.
• Interprete the different signs in the rock as we would letters in a book.
• This interpretation requires being part of the culture so that makes specific meaning of such signs
• REMEMBER: Data do no speak for themselves.

How Reading Takes Place

• Rocks contain single signs that inform on phenomena.
• Groups of signs can inform on environmental systems.
• Variations of sign groups in rock columns inform of environmental change over time.

Creating A History

• Massive subtidal deposits (sands) form the bottom layer.
• Thinly bedded intertidal deposits (sands and silts) form the second layer.
• A tidal channel cuts through the silts.
• The channel gets filled with sands, potentially forming a beach.
• There is possible sea level regression in this area over time.

Nicolas Steno

• Nicolas Steno (Niels Stensen), from Denmark (1638-1686) used precision instruments.
• His father was a jeweler.
• Steno became a famous anatomist who did dissections of once-living bodies.
• He moved to Italy and King Ferdinand II employed him.
• Steno wandered the Tuscan mountains, making observations and getting familiar with rocks.
• Dissecting a great white shark's head, he noted similarities between shark teeth and tongue stones.
• Steno questioned whether tongue stones could be shark teeth.
• Steno asked how shark teeth might be encased in mountain rocks.
• Steno published "De Solido" in 1669 to share his observations.

Principles of reading rocks

• Deposition of sedimentary layers usually occurs underwater.
• If lower layers are younger.
• Something has happened between deposition and now to change that.
• Sediments are laid down in laterally continuous layers.
• If the layers are not continuous, they may have been eroded
• Erosion usually resulted from running water
• Layers were originally laid down in horizontal layers.
• Evidence of deformation includes bending, folding, or doming.
• A feature that cuts across another is younger than what it crosses.
• Faults are younger than layers, including bends, if the fault doesn't bend itself.
• Erosion is the youngest feature, cutting across beds and faults.
• Steno created the history of Tuscany from his observations.
• Steno showed his observations, highly schematically, in figure 20.
• Steno's history goes back (21-25).
• The history can be recounted as follows:
• Flat, horizontal layers deposited most likely ended up underwater
• Flood waters erode layers and leave caves
• Caves collapse.
• Another flood spreads new continuous layers in all directions
• The waters recede while taking material and making caves
• Caves collapse again creating the landscape known today.
• Earth's surface is changing; it's dynamic.
• Earth history comes from assigning meaning to signs based on principles.
• The Earth's history is long, countered conventional wisdom that was Biblically based.
• A changing Earth was against conventional beliefs that Earth's history is young and permanent.
• Biblical work helped push geology forward.
• More than new data is required to shift understanding.
• Oftentimes it just takes looking at old data in a new way
• The signs used to find Steno's principles could not be signs of a changing earth until one was willing to allow for a changing earth

Earth's Chronology Development

• Earth's chronology was developed based on rock descriptions and fossils by the late 19th century.
• Eras were based on the signs of recorded life.
• Period names came from describing the original rocks of that age and major characteristics.
• Era and period boundaries reflected signs in the rocks.
• The sign in the rock are usually the appearance or disappearance of life forms (e.g., mass extinction events).
• Index fossils were very important in determining boundaries between periods.
• The term ‘Creta’ means chalk
• The term Triad is made of red beds, chalk, shale

Visible Geology Instructions:

• Use the Activity Sheet in D2L (content then titorials) and the Tutorial 2_Visible Geology_Primer
• Email group members in spreadsheet link, in the specified format.
• Begin by visiting www.visiblegeology.com/ and open the visualizer.
• Start adding geologic beds.
• From there, use the other buttons, play with all of them and see what they do.
• Use a continuous series of geologic beds to make up a history.
• Create up to 5 different phenomena.
• Add topography of your choice.
• Record your history.
• Take screen shots of your work
• Then interpret
• Deposition makes beds always underwater as well.
• Simple uniformity takes place in atmosphere.
• Faults record displacement across rocks.
• Dikes record intrusion.
• Folds or Tilting record responses.

Steps to Interpret

• Layers in order:

1. Oldest: Deposition (superposition)
2. Tilting (original horizontality)
3. Uplift/Erosion with and unconformity (cross-cutting)
4. Submergence/Deposition and Superposition)
5. Faulting
6. Igneous Intrusion
7. Youngest: Erosion into hill landscape

Explore how to decipher Earth's history by learning to read the rocks. Understand the rules of geology to discover the environment, ages, and behaviors of dinosaurs. Learn about stratigraphy and using rock layers to determine relative time.