Geological Features of Ice Ages in Ohio

My family moved from Ohio to Georgia during 1976 when I was 13 years old. I occasionally wonder how my life would have been different if we never would have moved. Would I have a blog entitled Ohio Before People instead of Georgia Before People? My interest in Pleistocene mammals began before we moved when I read a Time Magazine article about saber-toothed cat bones found at the First National Bank Site in Nashville, Tennessee. Maybe I would’ve had a natural history blog focusing on Ohio instead of Georgia.

Evidence of Pleistocene Ice Ages is abundant in Ohio because glaciers repeatedly advanced and receded over the state. Scientists believe there were 17 major glacial advances in Ohio over the past 3 million years, but geological evidence exists for just the last 2–The Illinoian (230,000 years BP-132,000 years BP) and The Wisconsinian (118,000 years BP-11,000 years BP). These last 2 glacial advances scoured away geological evidence of the previous 15, and the only geological evidence of the Illinoian glacial advance is south of where the glacier advanced during the Wisconsinian Ice Age. During the Illinoian Ice Age the glacier advanced all the way into northern Kentucky.

The following is the geological evidence of Ice Ages in Ohio.

Map showing the maximum extent of the most recent glacial advance during the Wisconsinian Ice Age. During the previous Ice Age, The Illinoian, the glacier advanced even further into northern Kentucky.

Lake Erie

All the Great Lakes were formed from melted Ice Sheet. Before Ice Ages began, the now extinct Erigan River System flowed through where the Great Lakes exist today. The advancing glacier took the route of least resistance and scoured out lake basins in this former river valley. There is no evidence of Great Lakes following previous Ice Ages, but it is likely there were previous incarnations of the Great Lakes. Present day Lake Erie is only 5000 years old, and it evolved from previous post-glacial lakes.

Kettle Lakes

Punderson Lake, a kettle lake in Ohio. Our family went for a picnic here in 1967 when I was 5 years old. A kettle lake is a melted chunk of glacier left behind when the glacier retreated.

Ohio is dotted with kettle lakes. They were formed when the glacier retreated but left big blocks of ice behind in low lying areas. Sometimes these blocks of ice became buried in sediment. Eventually, this melted ice became a small lake.

Kames

A kame in Scotland. (I couldn’t find a good photo of 1 in Ohio). Kames are sandy knobs that were outwash of sediment carried by meltwater streams on top of the glacier. When the glacier underneath melted, they slumped, but many are still higher than the surrounding terrain.

When the glacier was in the process of retreating, meltwater floods and wind often carried sediment on top of the ice sheet. This sediment piled up into hills. Eventually, the ice underneath melted, and the sediment slumped but was still higher than the surrounding terrain.

Moraines

Diagram showing sediment pushed forward by a glacier and left behind after it recedes.

Moraines are sediment pushed in front of glaciers. They appear as hills and show how far the glacier advanced. Glaciers alternately advanced and retreated. The most southerly moraines in Ohio show the farthest extent of glacier advance during the Last Glacial Maximum. Recessional moraines show where glaciers re-advanced during cold climate fluctuations after the Last Glacial Maximum. Spruce tree logs are commonly found buried in the moraines, showing where glaciers rapidly advanced through forests.

Outwash

The glaciers often melted rapidly, and the meltwater flooded down stream and river valleys carrying loads of sediment including gravel and sand. This sediment can be found in stream-like patterns throughout the state, though they are covered with vegetation. There are also lake sediments where the glacier blocked streams and rivers, forming temporary glacial lakes that eventually drained.

Erratics

Erratics are large boulders left behind by retreating glaciers. They are usually rocks not found in the region.

The glacier pushed big Canadian boulders into Ohio, leaving them behind when the ice melted. The big rocks do not match the local geology. The only Cambrian-aged rocks found in Ohio originated from Canadian outcrops.

The Shape of the Ohio River

Before Ice Ages began most rivers and streams in Ohio flowed north. But glaciers blocked the flow and forced the rivers to change course. The Ice Sheet shaped the course of the Ohio River which was actually created during the Ice Ages. Glacial advance extinguished a major Pliocene-aged river system known as the Teays. See also https://markgelbart.wordpress.com/2015/05/15/glaciers-shaped-the-ohio-river/

Reference:

Camp, Mark

Roadside Geology of Ohio

Mountain Press Publishing 2006

A Lake and 2 Rivers in Florida that Vanish

The Native-American name for Lake Jackson, located near Tallahassee, Florida, is Lake Okeeheebee, meaning disappearing waters. Local authorities should have kept the original name because there is another Lake Jackson in central Florida, and there is also a Lake Jackson in nearby Georgia. The existence of multiple Lake Jacksons in this region made researching this blog article confusing. I wonder what Native-Americans thought the reason was for the periodic draining of this lake. They probably invented some kind of mythical story. Modern geologists know the cause for the periodic disappearance of this lake. The lake sits on karst terrain where sandy soils prevail. Karst terrain consists of unevenly eroding limestone. Slightly acidic rain causes bedrock to erode, resulting in many underground caverns that often collapse into sinkholes. There are 2 sinkholes underneath Lake Jackson–the Porthole Sink and the Lime Sink. During dry spells when the water table falls, water from Lake Jackson drains into these sinkholes, just like water draining from a bathtub. Plant debris and mud will temporarily block the sinkholes, but eventually most of the lake will drain with the exception of small pools here and there where fish populations survive. The permeable sandy soils allow water to refill the lake following periods of higher rainfall that cause the local water table to rise.

Map and location of Lake Jackson in north Florida. From Wikipedia.

Lake Jackson when it is full of water.

Aerial photograph of Lake Jackson after its water vanishes. Lake Jackson is surrounded by wet prairie. From the Tallahassee Democrat by Daniel Martinko.

Lake Jackson is 6.2 square miles and averages 6 feet deep when it is full of water, though it is as much as 28 feet deep over the sinkholes. The lake has drained 14 times over the past 200 years, and it is currently in a drained stage. Surprisingly, periodic drainages are good for fishing. The draining reduces populations of the non-native plant hydrilla, and the re-filling stirs up nutrients, increasing food for rebounding fish numbers. Fishermen claim the fishing for largemouth bass, crappie, bluegill and redear sunfish, and bullhead catfish is excellent. The latter species is especially well-adapted for surviving in small pools during drainage phases. Though not mentioned on the internet, I’m sure bowfin, gar, and non-native tilapia thrive as well. Birdwatchers report the presence of herons, egrets, limpkins, eagles, ospreys, ducks, geese, fish crows, and least terns. It’s good habitat for alligators, turtles, and frogs too.

The karst terrain makes it difficult for rivers to flow in this region, and there are 2 rivers that vanish here. The Alapaha River, a tributary of the Suwannee River, simply disappears into the ground, flowing right into a sinkhole, and it emerges miles away. The Santa Fe River also disappears into a sinkhole, also to emerge miles away. Both become subterranean during part of their course. A river flowing into the ground is known as a swallet.

Photo of the Alapaha River where it vanishes into the ground. It re-emerges miles away.

Image of where the Santa Fe River vanishes. From a youtube video by Adlai, JN.

Reference:

Bryan, J., Scott, T., Means, Guy

Roadside Geology of Florida

Mountain Press Publishing Company 2008

When South Georgia was Deep Under Ocean Currents

An Atlantic Ocean shoreline occurred at the present-day location of the Georgia fall line along an axis from Augusta to Macon to Columbus. Immediately offshore the ocean was shallow, but farther off the coast ocean currents were strong and flowed over a deep channel. This channel originated from a suture or fault where part of the African continent formerly connected to North America before the supercontinent of Pangaea rifted apart. Following sea level rise, ocean currents began flowing over this natural low area about 99 million years ago. Geologists refer to it as the Suwannee Strait during the first 60 million years of its existence and the Gulf Trough from the mid-Eocene to the mid-Miocene. Sea level changes caused the low channel to shift to the northwest, hence the name change. The swift current that flowed over it was part of the clockwise-moving Gulf Stream, an ocean circulation pattern found all the way up the North American east coast. To the south of the Suwannee Strait/Gulf Trough were shallower seas dotted with coral reef islands. During the Oligocene a large island, known as Orange Island, though no oranges grew there yet, emerged above sea level south of the trough. The Gulf Trough was deepest during the late Eocene about 35 million years ago, and geologists think parts of it were 600 feet underwater. During the Miocene sediment washed down from eroding Appalachian Mountains began to fill in the Gulf Trough. In its later years of existence, it was a slow-moving narrower estuary. About 15 million years ago sea level fell and the Gulf Trough existed for a while as an above ground canyon. Today, this canyon is buried deep underneath millions of years of sediment, but there are exposed outcrops where rivers erode through this ancient sediment. However, a relic is visible underwater in the Gulf of Mexico, and it is known as Desoto canyon.

From 99 million years ago to 15 million years ago South Georgia was under deep ocean currents. Geologists refer to this area as the Suwannee Straight and the Gulf Trough. It reached its largest depth about 35 million years ago. The Atlantic Ocean shoreline occurred along the present day fall line. South of this trough was a shallower sea dotted with coral atolls and islands that periodically rose and sank according to changing sea levels.

Swift ocean currents carried well oxygenated sea water that supported abundant aquatic life in the Suwannee Strait during the Cretaceous. Monstrous mosasaurs and pliosaurs preyed upon bony fish, some species themselves armed with fangs. Sea turtles and sharks swam over beds of an extinct group of clams known as rudists that came in many different shapes and sizes. Ammonites, extinct cephalopods related to squids and octopi, thrived in Cretaceous seas. Today, most foraminifera are small and measured in millimeters, but oddly enough there were 4-inch-long species of foraminifera living in the Suwannee Strait, though they are one-celled animals related to amoeba.

Rudist clams were abundant in the Suwannee Strait during the Cretaceous era. They came in many different shapes. They went extinct along with the dinosaurs at the end of the Cretaceous.

During the Eocene primitive whales evolved and made the Suwannee Strait their home. The Suwannee Strait and later the Gulf Trough was still rich in fish, mollusks, and other sea life. Fossils in the limestone and shale deposits of Cretaceous through Miocene Age in the region are commonly found wherever erosional processes expose them, and the limestone itself is made of many ancient seashells.

Primitive whales swam alongside dugongs, sharks, bony fish, and turtles in the Gulf Trough during the Eocene. A skeleton of this species was found in Burke County, Georgia.

Notable fossils of Oligocene Age from the Gulf Trough include dugong, nautilus, and rhodoliths. A nearly complete skeleton of a dugong was found in a northwest Florida fuller’s earth mine. Today, just 3 species of nautilus are extant, and these occur in the Pacific and Indian Oceans, but apparently, they were common during the Oligocene in the Gulf Trough. Aturia alabamensis, a 2-foot-long nautilus, likely scavenged or actively hunted crustaceans on the sea bottom. Rhodoliths still exist but were especially abundant in the Gulf Trough during the Oligocene. Rhodoliths are species of red algae that resemble coral and also produce calcium carbonate. Rhodolith fossils are part of large fossiliferous limestone outcrops found in southwest Georgia and are thought to have occurred on the shallower flanks of the Gulf Trough.

Aturia alabamensis. This was a species of nautilus that grew to 2 feet long and was common in the Gulf Trough during the Oligocene.

Rhodoliths, red algae that resembles coral, was abundant in the Gulf Trough during the Oligocene. They are still extant.

DeSoto Canyon off the Florida coast is the only remnant of the Gulf Trough that hasn’t filled with sediment.

In the Beginning There was Proto-Earth and Theia

4.6 billion years ago, gravitational forces pulled enough star dust and rock together to form the planet Proto-Earth, and it began to orbit the sun, but another planet–Theia–shared the same orbit for 20-30 million years. According to the Giant Impact Hypothesis, the shared orbit eventually led to a collision between these 2 planets. Ejecta from the impact circled the Earth’s orbit for millions of years in a ring not unlike the ring that currently circles Saturn. Gravity consolidated the ring into the moon which had a much closer orbit then than it does today.

20-30 million years after Proto-Earth formed it was struck by another planet that occupied the same orbit.

The impact of the collision between Proto-Earth and Theia caused ejecta to orbit earth in a ring. This ring eventually consolidated into the moon.

Convincing evidence supports the Giant Impact Hypothesis. Earth’s spin and the moon’s orbit have similar orientations. Earth’s high momentum of rotation suggests the occurrence of an ancient impact. Analysis of moon dust indicates it was once molten–the result of a fiery impact that melted the ejecta that eventually accreted to form the moon. (Scientists refer to the consolidation of material into a planet as accretion.) The moon has a small core, suggesting most of Theia’s core fused with Proto-Earth’s core. The moon has small quantities of volatile elements, indicating most vaporized upon impact. Isotope ratios of zinc and oxygen on the moon are identical with those on Earth.

This is what the early Earth looked like after the moon consolidated. Widespread tectonic activity combined hydrogen and oxygen in rocks into water vapor released by volcanoes.

Earth is the most unusual planet in the solar system, and from what scientists can determine is unlike any known planet from other solar systems based on the limited data they can glean from such distant bodies. Water is abundant on Earth, while most planets are absolute deserts. Moreover, Earth is surrounded by an oxygen-rich atmosphere. Scientists wonder how earth accumulated water because they believe heat from the early sun was so great that most of the water on Proto-Earth boiled off. The prevailing theory posits meteorites and/or comets from the outer solar system delivered water to earth. However, a new study suggests water always existed in earth’s rocks. Scientists examined 13 inner orbit meteorites, known as enstatite chondrite meteorites, and determined they have the same isotopic ratios of various elements, including hydrogen, found in rocks on earth. Hydrogen and oxygen in earth rocks combined to form water that was released as vapor during volcanic activity. Proto-Earth likely formed from the accretion of enstatite chondrite meteors and asteroids within just a 5-million-year timespan. It’s mind-boggling to imagine how the consolidation of lifeless rocks led to our weird planet rife with so many different lifeforms.

Reference:

Piani, L.; et. al.

“Earth’s Water may have been Inherited from Material Similar to Enstatite Chondrite Meterorites”

Science 369 (6907) August 2020

Schiller, M.; M. Bizzarro, and J. Siebert

“Iron Isotope Evidence for very Rapid Accretion and Differentiation of the Proto-Earth”

Science Advances 6 (7) 2020

A Doomsday Glacier?

The alarmist headline of a recent article for the Rolling Stone magazine amuses me. It is entitled “The Fuse has been Blown, and the Doomsday Glacier is Headed for Us All.” This headline is a dramatic exaggeration. Yes, it is true–there is a fissure in an ice sheet on the Thwaites Glacier that scientists think is going to collapse within 3-5 years. And this collapse will likely cause sea level to rise by over 2 feet. But how soon sea levels rise that much is anybody’s guess because statistical models vary widely. Potentially, a sea level rise of this magnitude could inundate cities such as Miami, New York City, and New Orleans; but this change would likely take as long as a century, giving society plenty of time to respond. The glacier is not coming for us all.

At the present time warm salty ocean currents are flowing under the edge of the Thwaites Glacier, located in Western Antarctica. This warm current is melting the Ice Sheet, and this causes the discharge of icebergs. Scientists say the Thwaites Glacier alone already contributes to 4% of global sea level rise. When the Ice Sheet eventually collapses, thousands of icebergs will be discharged shortly after the collapse. However, this won’t directly cause sea level rise because this ice shelf is already floating on the water. Scientists fear the advance of the rest of the Thwaites Glacier (now on land) into the ocean is the mechanism that will cause dramatic sea level rise. Scientists can only guess how long this advance will take and how long it takes for the addition of this ice to raise sea levels.

Location of the Thwaites Glacier

Aerial photograph shows a massive ice shelf about to break off from the Thwaites glacier. Image from the New York Times.

Illustration showing how warm salty currents are undermining the ice shelf.

While researching information for this blog entry, I came across a comically contrarian editorial written by H. Sterling Burnett, of The Heartland Institute, a thinktank funded by oil companies to downplay the dangers of global warming. Dr. Burnett is a PHD, but he is deliberately dishonest or stupid. He notes temperatures in Antarctica have been stable for over 40 years and concludes there is no threat of sea level rise from the Thwaites Glacier because ice on the continent is not melting. He fails to understand or acknowledge the mechanism that could cause sea level to rise. It’s not temperatures on the continent but rather warm ocean currents undermining the edge of the glacier that could cause sea level rise. Dr. Burnett is simply a stooge for business crooks.

Photo of Burnett (from his editorial) and an excerpt from his column, demonstrating his ignorance of the mechanism that scientists fear will cause sea level rise. Burnett is paid to write propaganda for oil companies. His editorial downplaying scientists’ concern about the Thwaites Glacier is either deliberately dishonest or stupid.

References:

Goodell, P.

“The Fuse has been Blown, and the Doomsday Glacier is Coming for Us All”

Rolling Stone 2021

Kahn, J.

“The Doomsday Glacier is in Danger of Collapse Potentially Ominous News for Cities like New York, New Orleans, and Miami”

Fortune December 2021

Wahlen, A.K. et. al.

“Pathways and Modifications of Warm Water Flowing Beneath the Thwaites Ice Shelf, West Antarctica”

Science Advances April 5, 2021

Megalake Paratethys

The largest lake in earth’s history existed 11 million years ago and stretched across southern Europe and Asia. Its origins go back over 100 million years ago when the supercontinent of Gondwanaland split apart. The ocean that formed between the drifting continents is known as the Tethys Ocean. During the middle of the Miocene the Alps Mountain chain uplifted, cutting the Tethys Ocean into 2 halves. The southern half became the Mediterranean Sea, and the upper half turned into a massive freshwater lake known as Megalake Paratethys. This body of water existed for 5 million years, but further mountain uplift and climate change caused it to gradually recede. The freshwater lake shrank into an isolated salt lake and many individual lakes that fluctuated between salt and fresh. Today, the Black, Caspian, and Aral Seas are all that remains of Megalake Paratethys.

Map of Megalake Paratethys. Image from the below referenced sciencedailynews.com article.

Unique endemic whales lived in Megalake Paratethys. Image also from the below sciencedailynews.com article.

Megalake Paratethys hosted many endemic species found nowhere else. Whales and dolphins isolated from other ocean populations evolved into dwarf species, including the 9 foot long Cetatherium riabini. The grasslands that replaced the receding lake spawned the evolution of ancestors of modern day antelope, sheep, and goats.

References:

Paleoj, D. ; et al

“Late Marine Megalake Regression in Eurasia”

Scientific Reports 11 #11471 2021

Perkins, S.

“The Rise and Fall of the Earth’s Largest Lake”

http://www.sciencedailynews.org June 4, 2021

Permafrost as far South as Georgia during the Last Glacial Maximum

This is at least the 7th article I’ve written about Carolina Bays, but I keep coming across new and fascinating studies of these curious geological features. (See: https://markgelbart.wordpress.com/?s=Carolina+Bays ) These oval shaped depressions occur across the Carolinas and Georgia.  Their origins baffle scientists, but the commonly accepted explanation is they are topographical formations resulting from Ice Age wind and water erosion.  (Extraterrestrial explanations can be ruled out because Carolina Bays are of different ages, and there are 500,000 of them compared to just 250 known impact craters on the entire earth’s surface.)  I’ve long understood how wind and water erosion shaped the depressions, but I’ve never been satisfied with explanations for how the land initially subsided.  Some think wind simply blew unconsolidated sediment out of the pits, while I’ve suggested the land subsidence occurred due to peat fires (as occasionally occurs today).  In a new book Chris Swezey of the U.S. Geological Service proposed the initial subsidence of Carolina Bays was caused by discontinuous patches of permafrost that thawed during summers and collapsed.

Formerly, scientists thought permafrost (ground that stays frozen year round) extended as far south as northern Virginia during the Last Glacial Maximum, but Swezey believes there were patchy discontinuous areas of permafrost as far south as Georgia.  Carolina Bays resemble geological features found in southern Alaska today where permafrost is scattered and temporary.  The land swells and collapses and fills with water in oval depressions.  Northern Alaska hosts continuous permanent permafrost.

Discontinuous patches of permafrost create lakes in southern Alaska that resemble Carolina Bays located in the upper coastal plain of Georgia and the Carolinas.

Temperature graph showing average temperatures and sea level fall during the Last Glacial Maximum. Note the dips at about 27,000 and 24,500 years BP.  This is when discontinuous permafrost could have developed on some Georgia and Carolina soils.

I believe this map is misleading.  It shows the southern extent of the boreal forest zone, but zonal forest types as we know them today didn’t exist then.  From the below referenced paper.

Georgia must have been much colder during Ice Ages than I thought.  Most Carolina Bays formed between 35,000 years BP-15,000 years BP when glaciers expanded to cover Canada and New England.  Some date to earlier stadials of the Wisconsinian Ice Age.  Patchy permafrost in the Carolinas and Georgia likely occurred during especially cold phases of the Ice Age that probably lasted for decades rather than centuries.

Landscapes in Georgia during the LGM must have been varied and interesting.  Wetlands on Carolina Bays likely attracted summer populations of ducks, geese, and swans.  Sand dunes from dried out riverbeds rolled over the land, smothering mixed woodlands of pine, spruce, and oak.  Arid conditions favored grasslands that fed horse, bison, and llama; in turn pursued by giant lions and dire wolves.  Strange as it may seem, caribou and stag-moose ranged into this latitude.  Zonal vegetation as we know it didn’t exist then.  Instead, habitats were patchy and species compositions were dissimilar to those of any existing types of forest.  Local microclimates might favor oak thickets, open spruce woodlands, mature pine forests, grassy meadows, small marshy wetlands, or bare soil.  Less than 100 miles east of the inner coastal plain the climate was markedly warmer.  Land extending into what today is the Atlantic Ocean  hosted more warm weather species of plants and animals because it was closer to warmer ocean currents that moderated coastal climates.  Inland, the boundary between cold and warm climates frequently fluctuated, contributing to the patchy unstable environments unlike those of today.

Reference:

Swezey, Chris

“Quaternary Eolian Sand Dunes and Carolina Bays of the Atlantic Coastal Plain Province, USA”

in

Inland Dunes of North America

edited by Lancaster, Nicholas and Patrick Hesp

Springer Books 2020

 

 

The 57 Year Old Fire in Centralia, Pennsylvania

A month after I was born, the town fathers (or maybe they should be known as the village idiots) of Centralia, Pennsylvania thought it would be a good idea to burn the county landfill.  This garbage dump was located next to a coal strip mine in operation since 1935.  The fire ignited an underground coal seam, and it is still burning 57 years later.  3 major attempts to extinguish the fire failed.  Authorities estimate the fire will keep burning for another 250 years, and it will continue to release mercury, sulfur dioxide, nitrogen oxides, particulates, heavy metals, carbon monoxide, and carbon dioxide–all the poisons found in coal.  Heat from the underground fire buckles streets and kills trees.

Location of Centralia, Pennsylvania.

Aerial view of Centralia–abandoned homes and dead brown trees.

This road is destroyed and smoke sometimes comes through the cracks.  These photos and more can be found within this Business Insider article.  https://www.businessinsider.com/photos-of-abandoned-centralia-pa-2012-5#centralia-is-a-borough-in-the-northeastern-mountains-of-pennsylvania-in-2002-the-us-postal-service-revoked-the-towns-zip-code-17927-1

The town of 1,492 people became quite uninhabitable. During 1984 Congress allocated $42 million to relocate the residents, and the population today is 5.  I tried to determine if wildlife has moved into the area since the people left (like what happened at Chernobyl and the Korean demilitarized zone), but I can’t find anything about it.  For sure this ghost town is an example of the folly of man and in stark contrast to the blog article I wrote last week describing the travels of a man who visited Pennsylvania when it was still mostly a beautiful wilderness.

 

Migrating Carolina Bays

Referenced within the study I wrote about last week was another interesting paper that determined some Carolina Bays migrated.  I’ve written about Carolina Bays previously (See: https://markgelbart.wordpress.com/2012/04/30/a-young-carolina-bay-in-north-carolina/ ), but I did not know this.  Carolina Bays are elliptically-shaped depressions found in the Carolinas and Georgia, mostly on the coastal plain.  Wind and water erosion during wildly fluctuating Ice Age climates created these fascinating geological features.  Some are in the process of originating now.  Wind during cold arid climate cycles blew out unconsolidated sediment, and wind-driven water during wetter warmer cycles shaped them.  They vary in size and water content.  Some hold water year round, while others are seasonally dry.  They provide important wetland habitat, especially for amphibians because frog and salamander-eating fish are often absent.  Like so many other natural features, a majority of them have been destroyed by development.  Farmers drain and plough over them.

Scientists studied Herndon Bay in North Carolina.  They used ground penetrating radar to find abandoned rims, also known as lips. The abandoned rims date to 36.7, 29.6, and 27.2 thousand years old, and these dates are associated with climate cycle transitions.  In between these dates Herndon Bay stabilized.  Apparently, Herndon Bay was pushed by wind and moved across the landscape in a process that was too slow for the human eye to follow.  It has stabilized at different locations, and one could say this is a kind of migration across the landscape.

Ground Penetrating Radar Image from the below reference.  Note the former basins of Herndon Bay.  It has migrated across the landscape.

Carolina Bay located in Aiken, South Carolina.

Some crackpot scientists think Carolina Bays are craters formed by either comet impact ricochet or a comet striking a glacier, thus causing chunks of ice to fly thousands of miles before landing in southeastern North America.  A single fact debunks this idea–Carolina Bays originated at different times and some are still forming.  They are not the same age, ruling out a single extraterrestrial event.  There are 500,000 Carolina bays, yet less than 200 confirmed impact craters on earth, so this makes it seem highly unlikely as well that they result from multiple impacts.

Reference:

Moore, Christopher & Brooks, Mark & Mallinson, David & Parham, Peter & Ivester, Andrew & K. Feathers, James. (2016).

The Quaternary evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): implications for paleoclimate and oriented lake genesis.

Southeastern Geology. 51. 145-171.

 

Green Sahara Periods

I subscribed to The Economist magazine for awhile.  It’s an excellent magazine for news about world affairs.  I’m interested in world affairs, but not to the depth it gets covered in this periodical, and I recently decided not to renew my subscription.  Some of their articles are redundant because they’ll often have 2 articles in  1 issue about the same subject that say the same thing.  Their articles are also far too wordy.  The editors of this magazine need to learn how to be more succinct.  They could probably cut the word count of their articles by 75% and not lose anything in the translation.  In 1 of the last issues I read there was an article (actually 2) about the expansion of the Sahara desert.  The unnamed author of this article assumed the expansion of the Sahara desert was caused by man-made climate change.  His assumption was just plain ignorant.  Astronomically forced insolation can entirely explain the expansion and retraction of the Sahara desert.

Map comparing vegetation of North Africa during dry and humid climate cycles.  The Sahara desert becomes a lush environment at regular intervals that last for about 6,000 years.  The current natural cycle causes the present day arid conditions.

Scientists have determined  the Sahara desert becomes a lush environment with lightly wooded grasslands, lakes, and rivers at cyclical intervals.  They refer to these times as Green Sahara Periods.  Animal life colonizes the region during Green Sahara Periods, and the environment resembles the Serengeti Plain rather than the desert it is today.  The increase in moisture that transforms the desert into a rich natural community is caused by the 23,000 year variation in the earth’s wobble.  The earth normally spins like a top, and like the child’s toy this spin can wobble.  The wobble leads to a seasonal variation when the earth is closest to the sun (perihelion).  At the point in the cycle when earth is closest to the sun during summer, the amount of solar heat increases in this region.  This differential heating of the atmosphere causes low pressure systems to form over the Sahara, drawing in monsoonal precipitation from the Atlantic Ocean.  10 times more rain falls on the Sahara during humid periods than during present day conditions.  This transforms the region into a much more inhabitable environment.

Evidence of Green Sahara Periods dates to the late Miocene ~9 million years BP.  The last 4 Green Sahara Periods occurred from 6,000-10,000 years BP; 77,000-81,000 years BP; 102,000-108,000 years BP; and 122,000-128,000 years BP.  Notice 1 cycle was skipped.  This was during the Last Glacial Maximum when the earth was particularly arid.  Perhaps, other factors outweighed the 23,000 year cycle.  Scientists have noticed Green Sahara Periods have become less frequent since the mid-Pleistocene.

Evidence for Green Sahara Periods can be found on the land and in the ocean.  Explorers crossing the Sahara desert find dry lake beds and river drainages; and there are many rock paintings depicting scenes rich in wildlife that no longer occur in the region.  Samples of cores drilled from the ocean bottom find fluctuations in dust levels at regular intervals.  Sediment dated to dry periods contains high amounts of dust blown from land in sand storms.  Of course, the amount of sand greatly decreases during humid periods.  The shells of microscopic sea creatures, known as foraminifera, excavated from ocean cores also show isotopic variations that relate to changes in precipitation.

Rock painting in the Sahara desert depicting giraffes, goats, dogs, and people.  Giraffes no longer occur in this region.

The Green Sahara Periods influenced human history.  The rich environment allowed humans to expand from Africa into Asia across the Levantine gateway.  During desert cycles hunter-gatherers could not cross from 1 continent to the other.  1 study suggests humans may be hastening the expansion of the desert by grazing their livestock on the edges of the desert.  I don’t buy this.  Humans likely play a minor role compared to the natural cycle.  If precipitation increased, the desert would begin retracting, regardless of human activity.

Reference:

Larrasoara, J; A. Roberts, E. Rohlirn

“Dynamics of Green Sahara Periods and their role in Hominim Expansion”

Plos One 2013