Reading the Geologic Time Scale
Earth is approximately 4.6 billion years old. Geologists divide this enormous span of time into eons, eras, periods, and epochs based on major events such as mass extinctions, mountain-building (orogenies), and the appearance of new life forms. The Earth and Space Science Reference Tables (ESRT) page 6 shows this geologic time scale, while page 7 highlights important geologic events and fossil ranges in New York State.
How New York Was Built
Before the Atlantic Ocean opened, New York was part of a much larger landmass. The Grenville orogeny (about 1.0 billion years ago) metamorphosed the bedrock now exposed in the Adirondack Mountains and Hudson Highlands. Hundreds of millions of years later, the Taconian, Acadian, and Alleghenian orogenies built up successive mountain belts as continents collided. The Alleghenian orogeny — caused by the collision of North America and Africa — formed the supercontinent Pangaea. Pangaea later began to break up around 220 million years ago, eventually opening the Atlantic Ocean.
Fossils as Time Markers
Certain fossils are useful for telling time. An index fossil is the remains of an organism that lived for a short geologic period but spread over a wide area. Trilobites, eurypterids, and graptolites are classic New York index fossils. Today, the youngest rocks in New York — sands and clays beneath Long Island — record the most recent advance and retreat of continental ice during the last ice age.
Vocabulary Cards
Tap any card to flip it. Only one card opens at a time. Each card auto-closes after 8 seconds — but you can re-open it as many times as you need.
Matching Practice
Tap a term on the left, then tap its matching definition on the right.
Terms
Definitions
ESRT Page 6 — Geologic History
Tap the image to enlarge. Notice the columns: Era, Period, Epoch, and Life on Earth.
ESRT Page 7 — New York Events
Tap to enlarge. Pay attention to Important Geologic Events in New York and the Inferred Positions of Earth's Landmasses on the right.
Data Table — NY Index Fossils
Use ESRT pages 6 & 7 to complete the table. Each correct row contributes to your 4-point data table grade.
| Index Fossil | Group / Type | Era it Lived In | Existed When NY Was… |
|---|
Question Set — Part A
Answer all 10 questions. Each question is worth 1 point. Use ESRT pages 6 & 7 as needed.
Question Set — Part B
Answer all 10 questions. Each question is worth 1 point.
Print or Save Your Lab
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