INTRODUCTION
For a long time geologists have been bothered by several geological mysteries. One of the most famous is the fossil record of North America. The Early Paleozoic rocks of New England and the most eastern part of New York have a completely different fossil fauna and flora than the rest of the continent. The eastern grouping is distinctly European and has no resemblance to the western North American communities. The plants and animals are types that could not have swum across the present Atlantic Ocean. So, how did they get here? There were no birds to carry them and the ocean currents flow from North America to Europe so they did not drift across. The logical conclusion was that the Northeast had at one time been much closer to Europe.
Theory of continental drift: a theory that explains the formation, alteration, and extremely slow movement of the continents across the Earth's crust. The continents are thought to have been formed from one large landmass that split, drifted apart, and in places collided again.
EARTH
Earth is about 4.5 billion years old. The oldest rocks are about 3.9 billion years old. Continents and continental fragments have been sliding about on the earth’s molten core crashing into each other and moving apart as long as there have been masses of land on the earth. The initial land masses were hundreds of micro continents and island arcs. There were also supercontinents that were masses of land comprising more than one continent.
Ur was one of the first continents, formed three billion years ago. Ur consisted of small pieces of present day Africa, India, Australia and Antarctica. The continent Arctica followed a half a billion years later then another half a billion years passed before Baltica (northern Europe) and Atlantica (containing parts of eastern South America and Western Africa) emerged. The four continents roamed separately until, about one-and-a-half billion years ago, Arctica and Baltica collided with what is now eastern Antarctica to form the supercontinent Nena.
When Nena, Atlantica, and Ur came together one billion years ago, the supercontinent Rodinia was born. After 300 million years, the three landmasses separated for about 400 million years, then came back together in a new supercontinent, Pangaea.
For more than 100 million years most of the world’s land was united. About 200 million years ago, Pangaea broke up. When Pangaea came apart, Ur, Arctica, and Atlantica split up too. Parts of Ur went to Africa, Australia, and India, while Arctica became Canada, Greenland, and part of Siberia. Atlantica was divided between South America and Africa.
The continent, Laurentia, was made up of six former microcontinents between 2.5 and 1.5 billion years ago. Collisions with multiple continents thrust large amounts of sediment onto the eastern seaboard of Laurentia creating the high mountains that we now call the Grenvilles which stretched from northern Mexico, U.S. on to Canada and Sweden. The Grenvilles have been eroded, buried and modified by later collisions. The Grenville collisions and simultaneous collisions on the (present) western (then northern) side of North America resulted in the formation of a supercontinent, Rodinia, which straddled the equator and reached from pole to pole.
Rodinia broke into two pieces about 750 millions years ago. The land north of Laurentia (East Gondwana) drifted north. Laurentia and West Gondwana moved south near the South Pole then moved northward again.
About 600 million years ago most of the world’s large land masses came together again in the southern hemisphere and formed a new supercontinent, Gondwana. Laurentia and Baltica were nearby and united with Gondwanda to form an even larger supercontinent, Pannotia.
AVALONIA (or why Rhode Island is out of Africa)
Rhode Island began as a group of volcanic islands named Avalonia, off the coast of both Africa and South America south of the equator. Avalonia was a microcontinent and would eventually contribute to land in New England, other east coast US states, Canada, Ireland, England, Wales, Morocco, Portugal, Spain, France, Belgium, Holland and Germany. Avalonia was formed more than 565 million years ago. The earth’s crust moved and eventually the volcanic islands, rock from the ocean bottom and Africa crushed against the coast of North America. The colliding continents pushed up huge mountains and created most of the northern Appalachians. At one point, the peaks in Rhode Island were higher than the Himalayas.
For more than 100 million years, Jamestown was located deep within the supercontinent Pangaea. When Pangaea broke up, the Atlantic Ocean formed and slowly widened. As the Atlantic Ocean opened up its floor pushed apart like pie crust separated by bubbling filling. Africa’s crust split off from North America’s, leaving a piece of Africa behind which is now Beavertail, in Jamestown. The volcanic islands, the ocean bottom rocks, and the part of Africa left behind became Rhode Island.
ROCKS
You can find three different types of rocks in Rhode Island.
Igneous or “fire” rock formed when melted liquid rock or magma from inside the earth’s fiery interior pushed through the earth’s crust.
Sedimentary or “layered” rock is formed when sand, clay, gravel or shells compress into rock.
Metamorphic or “made-over” rock: Intense heat and pressure change igneous and sedimentary rocks into metamorphic rocks. Limestone becomes marble. Sandstone becomes quartzite.
ACTIVITY
Look at the different rocks in the area of the coordinates. The oldest bedrock in the Jamestown area is located in the Fort Wetherill area. Note the many quartz veins in the area.
Please email me the answers to these questions
1) What is the predominate type of rock (igneous, sedimentary, metamorphic) in the area of the coordinates?
2) The rocks in the Fort Wetherill area date to which period?
3) In your own words tell me how quartz veins are formed?
4) Give the approximate length and width in feet of the largest quartz vein seen in a westerly direction, across the inlet, extending from the cliff to the ocean.
...and post some pics.
Upload a photograph with your online log of:
1) You standing or sitting near a quartz vein.
2) Your GPS with visible coordinates on a sample of rock.
*Please use caution and commonsense in this area as there can be steep dropoffs. You must hold onto your children if they accompany you.