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New YorkEarth and Environmental Science

Geologic History and Dating

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do fossils help us match rock layers and read the history of life?

Explain how fossils form, what index fossils are, and how fossils are used to correlate rock layers between distant locations and to infer past environments, using the Reference Tables.
A Regents answer on fossils and correlation: how fossils form, the features of a good index fossil (widespread, short-lived, easily recognized), how index fossils and matching rock match (correlate) layers between distant outcrops, what fossils reveal about past environments and evolution, and how to read the Geologic History of New York State chart, with worked exam questions.
12 min answer →

How do we put a number of years on a rock or fossil?

Explain radioactive decay and half-life and use the Reference Tables Radioactive Decay Data to calculate the absolute age of a sample from the ratio of remaining radioactive isotope to its decay product.
A Regents answer on radioactive dating: what radioactive decay and half-life mean, the Reference Tables Radioactive Decay Data (Carbon-14 half-life 5700 years, Uranium-238 4.5 billion years), how to count half-lives from the ratio of parent to daughter, why Carbon-14 dates recent material and Uranium-238 dates ancient rock, with worked half-life calculations.
12 min answer →

How do we work out the order of events in the rock record without knowing exact ages?

Apply the principles of relative dating (superposition, original horizontality, cross-cutting relationships, inclusions and unconformities) to order events in a sequence of rock layers.
A Regents answer on relative dating: the law of superposition, original horizontality, cross-cutting relationships, inclusions, and how unconformities record missing time, used to put events in order in a cross-section, plus how faults, intrusions and contact metamorphism fit the sequence, with worked exam questions.
12 min answer →

What does the rock record tell us about New York's own deep past?

Use the Reference Tables Geologic History of New York State and the bedrock map to read New York's tectonic and environmental history, including ancient mountain-building, shallow seas and the most recent glaciation.
A Regents answer on New York's geologic history: how to read the Geologic History of New York State chart and the bedrock map together, the ancient mountain-building (orogenies), the shallow seas that left marine fossils and sedimentary rock, the oldest Precambrian rock of the Adirondacks, and the last ice age that shaped today's landscape, with worked exam questions.
12 min answer →

How is the vast span of Earth's history organized, and what does the time scale record?

Describe how the geologic time scale is divided (eons, eras, periods, epochs), how its boundaries mark major changes in life, and use the Reference Tables geologic time scale to read ages and events.
A Regents answer on the geologic time scale: the divisions (eons, eras, periods, epochs), Precambrian time and the Paleozoic, Mesozoic and Cenozoic eras, how mass extinctions mark era boundaries, Earth's age of about 4.6 billion years, and how to read ages and events off the Reference Tables Geologic History of New York State chart, with worked exam questions.
12 min answer →