Along the western coast of the Hudson River there are a series of scenic dark colored
cliffs.
These several hundred foot tall cliffs are exposed along a lengthy stretch of both New
Jersey and New York.
While they might not look like much, they represent the remains of a different period
of the planet's geologic history, when volcanoes dotted the landscape, and fresh lava flows
covered the region.
These cliffs are known as the Palisades and formed from ancient magmatic activity related
to numerous large scale volcanic eruptions, the likes of which have not been seen in modern
times.
These eruptions caused one of the planet's largest mass extinction events, and thus the
thick cliffs are related to that event which saw the extinction of numerous species such
as the phytosaur mystriosuchus planirostris.
The Palisades and their associated magmatic rock cover a wide swath of the tristate area.
Its rock exposure is 45 miles long, 1.3 miles wide, and averages more than 1,000 feet thick.
This feature is almost completely composed of a rock type known as diabase.
Diabase is an intrusive volcanic rock that forms when intrusions of magma solidify beneath
the surface.
Thus, because of this rock we known that the rock unit originated deep underground, which
in this case was determined to be a depth of 2 to 3 miles.
This makes the exposure a combination of a massive sill and group of magmatic dikes which
once prominently moved many thousands of cubic kilometers of molten rock to more distant
locations, eventually erupting onto the surface.
All of this occurred in a brief timespan between the end of the Triassic and beginning of the
Jurassic periods.
200 million years ago, much of the Earth looked like a completely different planet.
The climate was 5 degrees Celsius or 8 degrees Fahrenheit warmer than it is today, and large
swaths of the planet were covered in rainforests.
Numerous early dinosaurs existed, but they were relatively small, such as the species
known as Coelophysis which was 2 meters long and 1 meter tall.
In other words, dinosaurs of this era were at most the size of a modern crocodile monitor.
In these rainforests the first flowering plants had yet to form, so they were far less colorful
than their modern counterparts.
Also, sections of South America, North America, and Africa were joined together as part of
one massive supercontinent called Pangaea.
Although this continent had existed for 100 million years, it was at the end of its lifespan.
The mushroom shaped head of an underlying hotspot in the mantle had finally reached
the crust, causing large volumes of magma to pour onto the surface.
This hotspot caused the continents to slowly break apart, triggering even more volcanic
eruptions.
These eruptions were largely effusive, similar to those witnessed in Hawaii today.
However, individual so called "flood basalt" events covered tens of thousands of square
kilometers in lava.
Numerous flood basalt eruptions occurred at the same time in sections of modern Morrocco,
Brazil, and eastern North America.
However, the path molten rock took to the surface was not necessarily a straight line
upwards.
Rather, it zig zagged through the crust, forming large horizontal sills of material which occurred
through a single rock unit, and dikes which cut through several rock units.
The Palisades represents one of these magmatic conduits, transferring large volumes of magma
closer to the surface.
This magma would go on to erupt a several hundred foot thick layer of black volcanic
rock between the modern cities of Bound Brook and Ramsey in New Jersey.
One prominent exposure of this flood basalt can today be found to the north of Montclair
State University where the cliffs to the east represent the edge of the ancient flows of
lava.
Eventually, the magmatic conduit stopped transporting new material, and the basaltic composition
magma solidified as the rock type diabase.
These widespread flood basalts ejected large volumes of carbon dioxide into the atmosphere,
causing much of the oceans to turn acidic and raising the average temperature.
This caused the subsequent mass extinction which in a mere 10,000 years caused 30% of
all marine species to go extinct.
In the 200 million years since, much of the rock overlying this sill has eroded away,
and in addition to a 15 degree tilt has allowed a large segment of ancient volcanic rock to
become visible on the surface.
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