By S. Robinson
The Geological History of Earth & Wisconsin Rocks & Fossils
VIDEOS (coming soon)
CLICK ON ANY IMAGE TO ENLARGE
Wisconsin State Resources
See rocks, beach glass, fossils and other treasures I've found here: Identifying Lake Michigan Rocks & other treasures! Other than the author (me), some Images courtesy Wikipedia, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license or coyright by S.R. Robinson.
*** A PERSONAL STUDY GUIDE ***
Earth's Geological History
LET'S START AT THE VERY BEGINNING...THE TIMELINE OF THE UNIVERSE
First, put the age of the universe in perspective, view the 'cosmic calendar'.
The Cosmic Calendar is a method to visualize the chronology of the universe, scaling its currently
understood age of 13.8 billion years to a single year.
In this visualization, (above) the Big Bang took place at the beginning of January 1 at midnight, and the current moment maps onto the end of December 31 just before midnight.
At this scale, there are 437.5 years per cosmic second, 1.575 million years per cosmic hour, and 37.8 million years per cosmic day.
The concept was popularized by Carl Sagan in his 1977 book The Dragons of Eden and on his 1980 television series Cosmos.[2] Sagan goes on to extend the comparison in
terms of surface area, explaining that if the Cosmic Calendar were scaled to the size of a football field, then "all of human history would occupy an area the size of [his] hand".
Note that our Milky Way Galaxy, in the cosmic calendar visualization, did not form until May!
And our Solar System didn't form until sometime in September!
Click here to view a more detailed view of the Cosmic Calendar
SO...ABOUT 4.6 BILLION YEARS AGO...A NEW SOLAR SYSTEM AND A SMALL LITTLE PLANET FORMED, IN AN UNREMARKABLE AREA OF THE MILKY WAY GALAXY...WE CALL THIS PLANET EARTH.
BY THE TIME EARTH AND OUR SOLAR SYSTEM FORMED, THE UNIVERSE WAS ALREADY VERY OLD.
WHAT HAPPENED HERE? HAS IT HAPPENED ANYWHERE ELSE?
GEOLOGICAL TIME SCALE OF PLANET EARTH & Wisconsin - Various Graphs
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2
3
4
Continents over Time
EARTH HAS A VERY VIOLENT HISTORY, VOLCANIC ACTIVITY COVERED THE ENTIRE PLANET FOR EONS.
THINGS STARTED SETTLING DOWN A BIT ABOUT 750 MILLION YEARS AGO...
however, as you can see, the surface of earth, its crust and continents are constantly on the move.
This activity has created huge mountain ranges, oceans, deserts, snow ball earths, vast lava and glacial fields, etc.,
changing over time, creating, destroying, creating - again and again.
The red dots on the planet indicate the changing locations of Missoula, MT and Milwaukee, WI, a journey across the globe.
My hometown, and now my current home, respectively.
PLATE MOVEMENTS OF THE PAST AND THE FUTURE
VARIOUS GEOLOGICAL EPOCHS of WISCONSIN & ARTISTS' RENDITIONS OF EARTH'S PAST
PALEOZOIC ERA - (550-200 MILLION YEARS AGO)
PALEOZOIC ERA- CAMBRIAN EPOCH (Approx. 500-550 MILLION YEARS AGO)
PALEOZOIC ERA - ORDIVICIAN EPOCH (Approx. 500-450 MILLION YEARS AGO)
The oldest fossil found in Wisconsin = Calymene celebra
This trilobite lived in the warm shallow waters covering much of North America during the Late Ordovician and Early Silurian (~ 460-430 million years ago). The first specimen was collected in the 1830s, but since then, thousands of specimens of this fossil have been recovered. Here are some of the crinoid discs and stems I've found on the shores of Lake Michigan (Wisconsin side). They are usually tiny, no larger than my pinky fingernail.
PALEOZOIC ERA - SILURIAN EPOCH (Approx. 450-400 MILLION YEARS AGO)
PALEOZOIC ERA - DEVONIAN EPOCH (Approx. 400-350 MILLIONS YEARS AGO)
An overview of the continental plates on Earth, and earthquake history
Identifying the three types of Rock, Igneous, Metamorphic and Sedimentary
The Rock Cycle
Identifying Minerals
If you have a solid knowledge of minerals, you can more easily identify rocks.
IGNEOUS
The term “Igneous” is derived from the Latin word for fire. It is an appropriate term since all igneous rocks are
formed from molten materials (magma) that solidified after cooling. Igneous rocks that formed deep below the
surface of the earth as the magma forced its way into the crust are termed intrusive rocks. Common igneous
intrusive rocks found in Wisconsin include granite, diorite, syenite, and gabbro. Rocks that formed from magma
reaching the earth’s surface as lava flows, or other volcanic material, are termed extrusive rocks. Some of the
most common extrusive rocks in the state are basalt, felsite, and rhyolite.
Igneous rocks have crystalline structures that range from very coarse to very fine,
typically have high specific gravities, and tend to be very hard material. The most common igneous rock in
Wisconsin is granite. Erosion and weathering of the
igneous rocks and associated metamorphism provided the materials from which the sedimentary rocks were
formed. In Wisconsin, igneous rocks are some of the oldest rocks, and are found near the surface in roughly
the northern third of the state. They also extend under the southern portion of the state, but are buried by
hundreds, to as much as several thousand, of feet of the younger sedimentary rocks.
COMMON WISCONSIN IGNEOUS ROCKS
METAMORPHIC
Metamorphic rocks are those derived from the alteration of existing rocks by heat and pressure over long periods of time. Igneous, sedimentary, and even older metamorphic rocks can be altered by this process. The development of sufficient heat and pressure to create changes to the crystalline structure of the original rock can result from a number of conditions including earth crustal movement, pressure from increased overburden, and tectonic activity. The resultant metamorphic rocks often exhibit an increased competency and a more pronounced crystalline structure. Metamorphic rocks occur widely across the northern third of the state in complex associations with igneous rocks. However, there are also several significant exposures in southern Wisconsin including the Baraboo and the Waterloo quartzites.
The most common metamorphic rocks found in Wisconsin:
Bedrock Type ---- Parent Material
Schist -----------Basalt, Gabbro
Gneiss ---------- Granite
Greenstone ------ Basalt
Quartzite ------- Sandstone
Slate ----------- Shale
The igneous and metamorphic rocks are the oldest in the state of Wisconsin and fall into the Precambrian time period.
The rocks range in age from approximately 1 billion years to about 2.8 billion years(!),
and form the bedrock surface under most of the northern portion of the state.
Metamorphic rocks are existing rocks that have been heated, put under pressure or both. All rocks can become metamorphic, and under go these changes.Even a metamorphic rock can be further metamorphosed!
SEDIMENTARY
Sedimentary rocks are those rocks formed through the deposition and solidification of sediment transported by water, ice or wind. A characteristic feature of sedimentary rocks is a layered structure known as bedding or stratification (AGI, 1972). The mineral portions of these rocks resulted from the erosion of rocks of earlier ages, while the organic portions originated from the accumulation of shells and skeletons of various marine creatures existing at the time of deposition. The wide spread distribution of water-lain sedimentary rocks in the state shows that Wisconsin was covered by oceans for many millions of years. The most common sedimentary rocks found in the state are sandstone, shale, and limestone/dolomite. Sandstone is formed from the near-shore deposition of sand sized materials eroded from adjoining uplands and carried to the shore by water or wind. In Wisconsin, sandstones are composed primarily of quartz particles. Bedding is often visible in exposed rock faces which attests to the water borne origins of these rocks. The individual sand grains in the sandstone mass vary from coarse to fine, depending on the mechanics of deposition. Sandstone is formed when the individual grains are cemented together by silica and other minerals to form a coherent mass. However, variations in the type and degree of cementing agents cause sandstones to vary from hard, competent rock, to soft poorly cemented material. Sandstones are found in a broad arc across the northwestern and central parts of the state. Shale is formed in a process similar to that of sandstone, but deposition occurred further away from the shore line and/or in deeper water. As a result, the individual grain size of the material is predominantly in the clay, and to a lesser extent silt, sized fraction. This gives the rock a fine grained appearance. However, at times the transition zone from sandstone to shale was gradual or uneven which resulted in shaley sandstones or sandy shales. In Wisconsin, shale tends to be a rather weak rock that weathers easily, making surface exposures of this rock uncommon. Shale is found in a narrow band in eastern Wisconsin, and in association with sandstone in western Wisconsin. Limestone is termed a carbonate rock because of the high percentages of calcium carbonate found in its matrix. Limestone is formed in deeper water environments, from the accumulation of the shells and skeletal remains of sea creatures, along with the precipitation of calcium carbonate from the sea water. In Wisconsin, much of the rock originally deposited as limestone has been changed to dolomite (dolostone) by the gradual chemical replacement of calcium by water borne magnesium. (Shultz, 1986) Limestones and dolomites often contain fossils of some of the sea creatures that existed at the time of the rock formation. Fluctuating conditions during formation created shaley zones or layers in some of the carbonate rocks. However, most of the carbonate rocks tend to be dense, strong material, and are often used for construction. The carbonate rocks are widespread in a broad arc extending across much of southern and eastern Wisconsin.
What about Wisconsin?
Geological Scale, FOCUS on Wisconsin
The bedrock geologic record in Wisconsin is divided into two major divisions of time: the Pre- cambrian, older than 600 million years, and the Paleozoic, younger than 600 million years. The Precambrian rocks are at the bottom and consist predominantly of crystalline rocks.
Identifying Fossils and Rocks of Wisconsin
Here we have a very dense plate of crinoid plus other fossils. The rock matrix is Fossiliferous Limestone. Also seen are bryazoans, a brachiopod shells, a spikey point (forgot the name) and what else??
These creatures lived in a shallow ocean some 400 million years ago. At the time they died, Wisconsin (the red dot below) was South of the equator!
CRINOIDS!!
PETOSKEY STONE FROM A FRIEND (NOPE, NOT FOUND AROUND HERE)
BANDED IRON FORMATIONS
MY COLLECTION OF ROCKS
HOW GLACIERS FORM
WISCONSIN MAPS
ROCK BASICS
ROCK ID WITH THE HELP OF 'MICHIGAN ROCKS' AND DR NAT
PLATE 19
CHALCEDONY
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VIDEOS
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Identifying Fossils
Here we have a very dense plate of crinoid fossils. The rock in Fossiliferous Limestone. Also seen are bryazoans, a brachiopod shell perhaps, a spikey point (forgot the name) and what else??
WHAT IS THIS?
WISCONSIN STATE RESOURCES
BEDROCK GEOLOGY OF WISCONSIN - - - - - - - - WAUKESHA FAULT - - - - - - - - WISCONSIN AQUIFERS
BEDROCK GEOLOGY OF WISCONSIN - - - - - - - - WAUKESHA FAULT - - - - - - - - WISCONSIN AQUIFERS
WOW!
A brand new 'Quaternary Geology of Wisconsin' map! (2025)
This is an amazing resource for professional and even us amateurs; it identifies the sediments deposited by glaciers over the last almost 3 million years.
"Published by UW-Madison Extension’s Wisconsin Geological and Natural History Survey tells the story of how the landscape was shaped over the last 2.58 million years.
'Quaternary Geology of Wisconsin' describes the blanket of sediment that covers Wisconsin’s solid bedrock and how it got there. These deposits reveal evidence of
ice sheets, wind, water, and erosion and hint at the deep geologic history of Wisconsin and the lasting effect it has on our daily lives".
Thank you to the WGNHS Quaternary geologists:
J. Elmo Rawling, III
Eric Carson
LINKS
Watch a video of the Earth Through time