Step 1
Burial & Stone Formation
Dead marine organisms, mud, silt, and calcium carbonate settled layer upon layer onto the calm seafloor.
Explain how immense pressure and chemical changes transformed loose mud into solid sedimentary rock (shale and limestone):
Step 2
Mountain Building Collision
The Earth's crust is divided into shifting plates. Continents collided in a massive mountain-building event (the Appalachian orogeny).
What happened to the deeply buried marine strata when continental plates collided? How did this lift seafloor rocks thousands of feet?
Step 3
Surface Exposure
Once tectonic forces pushed the sedimentary rock upward into dry land, it was relentlessly exposed to the elements.
How did wind, rain, rivers, and Ice Age glaciers expose 380-million-year-old Devonian shale at the surface today at Penn Dixie?
Key Geologic Principle: Ocean water did not evaporate away; tectonic forces elevated the seabed thousands of feet, and erosion stripped away younger overburden rocks!
Life in the Devonian Period • Student Field Guide Page 2 of 3
Scientific Argumentation
Student Name:
The Skeptic's Challenge
A visiting student looks out at a snowy Buffalo winter and asserts: "There is no way Western New York was ever an ocean! We are hundreds of miles from any ocean, and tropical corals cannot live in the cold."
Construct a complete scientific argument (Claim, Evidence, and Reasoning) using fossil data and rock evidence from Penn Dixie to refute this skeptic.
1. Claim Write a clear, direct statement answering what Western New York was like during the Devonian Period:
Identify the type of body of water, climate, and geographic position 380 million years ago.
2. Evidence Provide scientific data and fossil observations to back up your claim:
Cite at least TWO specific fossils (e.g., Eldredgeops, brachiopods, horn corals) and name the sedimentary rock type.
3. Reasoning Explain the scientific principles that connect your evidence to your claim:
Explain why these creatures could only survive in saltwater, why corals require warm sunlit water, and how plate tectonics moved NY.
Detective Self-Check Checklist:
Accurate Devonian claim stated
2+ specific fossils & rock named
Marine adaptations & tectonics explained
Life in the Devonian Period • Student Field Guide Page 3 of 3
Devonian Sea Detectives • Teacher Facilitation Guide Page 1 of 2
Answer Key & Scoring Guide
Teacher Key
A. Trilobite (Eldredgeops rana):
Key takeaway: Exclusively marine bottom-crawlers and scavengers. Their presence proves a muddy, calm saltwater sea bed rich in organic debris.
B. Brachiopod ("Lamp Shell"):
Key takeaway: Marine sessile filter feeders anchored to the seafloor. Thousands crowded together indicate a productive, nutrient-rich shallow sea.
C. Crinoid ("Sea Lily"):
Key takeaway: Echinoderms that thrive in gentle, clear, shallow currents. Columnal discs prove submerged reef gardens.
D. Horn Corals & Ammonoids:
Key takeaway: Corals require warm, sunlit photic zone waters. Free-swimming ammonoids prove an active open-water food web (nekton).
Step 1 (Lithification): Over millions of years, thick layers of dead marine organisms, fine mud, and calcite accumulated. The immense pressure of overlying strata squeezed out fluids and cemented sediments into shale and limestone rock.
Step 2 (Tectonic Uplift): Tectonic plates collided during the Acadian/Appalachian orogeny (mountain building). Crustal compression forced the marine sedimentary rock upward thousands of feet above sea level into elevated land.
Step 3 (Weathering & Erosion): Over the last several million years (including Ice Age glaciers and modern running water), weathering and erosion scraped away younger rock layers, exposing the 380-million-year-old Devonian shale at the surface today.
Exemplar Claim: Western New York was once a warm, tropical shallow saltwater sea (the Kaskaskia Sea) located south of the equator during the Devonian Period.
Exemplar Evidence: Thousands of marine fossils are preserved in gray shale at Penn Dixie in Hamburg, NY, including Eldredgeops trilobites, brachiopods, crinoid stems, and horn corals. These organisms are embedded in sedimentary rock formed from ancient mud.
Exemplar Reasoning: Trilobites, brachiopods, and corals cannot survive on dry land or in fresh water—they are strictly saltwater marine species. Horn corals specifically require warm, shallow, sunlit water to build calcium carbonate reefs. While Western New York is cold and inland today, plate tectonics moved North America northward over 380 million years, and tectonic uplift followed by erosion exposed this ancient ocean floor on dry land today.
Claim (2 pts) States clearly that WNY was a warm shallow sea during the Devonian.
Evidence (4 pts) Cites at least 2 specific marine fossils AND mentions the sedimentary shale/limestone rock.
Reasoning (4 pts) Connects fossil life requirements to saltwater/tropical conditions and explains tectonic/erosion shift.
Devonian Sea Detectives • Teacher Facilitation Guide Page 2 of 2
Tropical Coral Reefs
Massive colonies of coral and solitary "horn corals" (shaped like small animal horns) covered the shallow seafloor. Corals need clear, warm, sunlit saltwater to survive. Along with marine snails (gastropods), they built giant reef habitats teeming with life.
Devonian Vocabulary Spotlight
Epicontinental Sea: A vast, shallow sea that temporarily floods the interior of a continent.
Shale: A soft, fine-grained sedimentary rock formed by the compaction of clay and mud.
Life in the Devonian Seas • 6th Grade Earth Science Article Page 1 of 2
Part 2: Predators & Geologic Forces
Penn Dixie Science Reader
New York State Fossil
The most famous fossil found at Penn Dixie is the trilobite Eldredgeops rana. Trilobites were armored arthropods, ancient ancestors of today's horseshoe crabs and lobsters. They crawled along the muddy seafloor scavenging for organic bits.
They had compound eyes made of pure calcite crystals, giving them sharp vision underwater. When danger approached, an Eldredgeops rolled into a tight, armored ball—just like a modern pillbug or armadillo!
The Age of Fishes
Above the seafloor, swift swimmers ruled the open water. Ammonoids were squid-like cephalopods that lived inside coiled, spiral shells. By filling tiny inner chambers with gas, they floated and steered easily while hunting with tentacles.
The Devonian is called the Age of Fishes because early sharks and heavily armored fish (placoderms) with bony plates dominated the seas, hunting trilobites and ammonoids.
How did a tropical ocean that existed 380 million years ago become dry land in Western New York? It didn't happen overnight. It took three major geologic steps over hundreds of millions of years:
1. Sediment Accumulation & Lithification (Turning Mud to Stone):
When creatures died, they sank into the soft seafloor silt. Over millions of years, feet upon feet of new mud piled on top. The immense pressure and dissolved minerals squeezed out water and cemented the mud into solid rock layers: shale and limestone, trapping the animals' shells inside.
2. Tectonic Uplift & Mountain Building (Orogeny):
The Earth's crust is made of giant colliding plates. Around this time, continental plates slammed into eastern North America, crumpling the land to build the Appalachian Mountains. This immense tectonic squeeze forced the deep marine rock layers thousands of feet upward, lifting the old seafloor high above sea level!
3. Weathering & Erosion (Uncovering the Ancient Secrets):
Once the rock was elevated, wind, rain, rushing rivers, and massive Ice Age glaciers wore away the younger top layers of rock. After millions of years of natural erosion and quarrying, the 380-million-year-old Devonian shale was finally exposed right at the surface for fossil hunters today.
1. Habitat Clue Why do horn corals and crinoids prove the water was warm and shallow rather than freezing deep ocean?
2. Anatomy Clue What two physical adaptations helped Eldredgeops trilobites survive on the muddy seabed?
3. Earth Process Clue What caused the seafloor rock layers to rise high above sea level into modern Western New York?
Life in the Devonian Seas • 6th Grade Earth Science Article Page 2 of 2
