Time and delaware

• HISTORY OF DELAWARE

Section Goals

• Where does Delaware fit into the big picture of plate tectonics?

• What is the geologic history of Delaware?• What evidence supports our interpretation

of Delaware's geologic history?

Delaware’s interesting history

• If you lived here 450 million years ago, your home and school would have been located in a mountain village with nearby volcanoes and the potential for large earthquakes.

• If you lived here about 18 million years ago, you could have been swimming with a freshwater porpoise in a river that was flowing to a nearby ocean.

• About 12,000 years ago, you'd better hope that you hadyour winter coat on, as the climate was much colder with glacial ice in Pennsylvania andthe melt water from those glaciers flowing across Delaware's frozen landscape.

HOW DO WE KNOW ALL THIS ABOUT OUR STATE?

• The evidence for these events comes from examining the rocks and sediments that occur in Delaware and making inferences from this evidence about how these rocks and sediments were formed.

Lab Goals

• Review the geologic time scale and place modern time within the eons, eras, periods and epochs of the scale.

• Observe the generalized geologic map of Delaware and the geologic maps ofDelaware's New Castle and Kent Counties.

• Based upon observations from these maps, identify some of the major rocks and sediments that occur in Delaware.

Main Ideas

• The geologic time scale is used to organize Earth's 4.55 billion year history.

• The geologic time scale is divided up into a series of units: eons, eras, periods and epochs. The eons cover the longest periods of time (billions to many hundreds of millions of year); the epochs cover the shortest periods of time (tens to hundreds of thousands of years).

Sediments• Delaware is underlain by metamorphic and igneous rocks.

These rocks are exposed at/near the surface in the northern portion of New Castle County. They are metamorphic and igneous. These rocks are old, dating back to the latest part of the Proterozoic Eon and the earliest part of the Phanerozoic Eon within the Paleozoic Era (approximately 400-600 million years ago).

• They.were formed at a time when Delaware was part of a convergent plate boundary. These igneous and metamorphic rocks became part of a very large mountain chain, as high in elevation as the modern day Himalaya Mountains in Asia, or the Andes Mountains in South America.

Sediments

• The metamorphic and igneous rocks throughout most of Delaware are covered

by sediments. The thickness of these sediments steadily increases from northwest to southeast from less than 1 meter in the northern portion of the state to over 3,000 meters in the south.

• The source of most of these sediments is from the continuing weathering and erosion of the Appalachian Mountains. This has been occurring for over the last 400 million years. These weathered sediments are carried by water (via rivers and streams), ice (when glaciers occurred in Pennsylvania), and wind andeventually deposited.

Sediments

• The sediments of Delaware were mostly deposited in either river (sometimes called fluvial), marine (i.e., coastal or shallow water), or glacial environments. In the present day, sediments are being deposited in Delaware on land and near the coast in swamps and marshes and in portions of Delaware Bay.

Geology

• The rocks and sediments in Delaware are an example of the rock cycle. Although, our sediments have not yet been lithified into sedimentary rocks, they still demonstrate how previously existing rocks, like the igneous and metamorphic rocks of Delaware, are weathered, eroded, and deposited, where they can then be lithified into sedimentary rocks.

Energy of Plate tectonics

• The energy that drives the rock cycle comes from two sources. The Earth's internal energy source ultimately drives the tectonic plates and causes the formation of divergent plate boundaries — where the igneous rocks of Delaware were formed — and convergent plate boundaries — where the metamorphic rocks of Delaware were formed.

External energy for formation of sediments

• The external energy that the Earth receives from the Sun determines climate and drives the water cycle that in large part is responsible for the weathering and erosion of pre-existing rocks that leads to the subsequent deposition of the sediments that will become sedimentary rocks.

Overview of lab• This lesson begins by reviewing the geologic time scale.

This is followed by an examination of the generalized geologic map of Delaware, determination of the location of your school on the map and the age and types of surface or near-surface rocks or sediments occurring near your school. The geologic maps of New Castle and Kent County will be used to investigate the geologic history of Delaware. Groups of students will give presentations on selected rocks, deposits or formations and the class will see how these rocks and sediments can be used to infer the geologic history of Delaware.

• Finally, the rocks and sediments of Delaware will be used to study the rock cycle.

• This lesson brings plate tectonics to Delaware. Earthquakes and volcanoes seem very far away and unrelated to our area. Since in Delaware we are currently in a phase of the rock cycle that is dominated by erosion/deposition, much of our geologic history is not visible to the average resident. This lesson on the geologic history of Delaware puts students into the overall picture of global plate tectonics, emphasizing the slow rate at which these changes take place.

Age of Earth

• The best estimate of the Earth's age is 4.55 billion (4,550,000,000) years. That's a lot of years.

Dividing time• To try to organize that lengthy period of time into

something that is manageable, geologists use the geologic time scale. You were first introduced to the geologic time scale in the 6th Grade Earth History Unit.

• You might remember that unit as the time that you learned about the Grand Canyon and the rocks and fossils that occur within the canyon. As a review, or maybe learning for the first time; the geologic time scale is divided into a series of distinct units of time: eons, eras, periods, and epochs. The eons cover the longest periods of time (billions to many hundreds of millions of years); the epochs cover the shortest periods of time (tens to hundreds of thousands of years).

Book analogy for divisions of time

• As an analogy, the geologic time scale is organized like a book. In this comparison, the eons are equivalent to the chapters in a book, the eras are the paragraphs within a given chapter, the periods would be equivalent to the sentences within this paragraph, and the epochs would be equivalent to the individual words within a sentence within the paragraph.

Time scale info

• Make sure students are shown a time scale where the precambrian is divided up into 3 sections

• The term Precambrian is no longer in favor by many geologists and the eons Hadeon, Archean and Proterozoic are now used to define this early period of time.

Questions on time scale

1. If the "book" associated with the geologic time scale was entitled "The History of the Earth", what would be the title of Chapter 1 of the book? HINT: Geologists start with the intervals of time that occurred the longest time ago.

2. How many other chapters would there be in this book and what would their titles be?

3. Within the Phanerozoic Eon, what name for an interval of time would be an example of a paragraph within the chapter entitled "Phanerozoic “

Questions on time scale

4. Within the Mesozoic Era, what name for an interval of time would be an example of a sentence within this paragraph?

5. Within the Quaternary Period during the Cenozoic Era in the Phanerozoic Eon, what name for an interval of time would be an example of a word within this sentence?

6. In what Eon, Era, Period, and Epoch do we currently live and how many years ago did each of these units of time start?

Answer to last question

Phanerozoic Eon (started 570 million years ago), Cenozoic Era (started 66.4 million years ago), Quaternary Period (started 1.6 million years ago), Holocene Epoch (started 0.01 million years ago (10,000 years ago))

Time in terms of Delaware

• Shown below is a generalized or simplified) geologic map of Delaware. A geologic map is a map that shows the types of rocks, sediments, or formations (groups of rocks or sediments) that occur at the surface, or just beneath the surface (below the soil). This map was produced by the Delaware Geological Survey (web link:

• http://www.dgs.udef.eduipublicationsipubs/SpecialPublicationsispl

Geo Map of delaware

Key:

Questions based on the map

1. What is the approximate age of the oldest rocks in Delaware?2. Where are these rocks located?3. What is the approximate age of the youngest sediments in

Delaware? HINT: Swamps and marshes are areas where fine-grained sediments like silt and clay, along with lots of plant material, are deposited.

4. Where are these sediments located?5. What is the name of the rocks, sediments, or formation that is

found at/near the surface where your school is located?6. What are the approximate ages of the rocks, sediments, or

formation that are found at/near the surface where your school is located?

Note to teachers

• Marshes and swamps are areas where fine-grained silts and clays, along with lots of plant material, are deposited. There are also some areas in Delaware Bay where mostly fine-grained, silt- and clay-sized sediments are being deposited, but these depositional zones are not included in the generalized geologic map of Delaware.

Answer to question 5• Determine the approximate location for your school

on this map. If it occurs within the • purple — metamorphic and igneous rocks;• green — formations (groups of sediments) that are

Cretaceous (144-66 million years) in age; • orange — Bryn Mawr Formation; • tan = Columbia or Beaverdam Formations; • gold — Old College Formation; • light green — Nanticoke deposits; • bright yellow — Delaware Bay Group; • brown — swamp or marsh deposits

Answer to question 6• Determine the approximate location for your

school on this map. If it occurs within: • purple — 600-400 million years;• green — 144-66 million years;• orange — 36.6-5.3 million years; • tan = 5.3 million — 10,000 years; • gold — 1.6 million — 10,000 years; • light green — 1.6 million — 10,000 years; • bright yellow — 1.6 million —10,000 years;• brown -10,000 years to today