1. Geological Time

2. Geologic Time Scale
Geologists have subdivided geologic time into units based on fossil evidence.
This division of time is called the Geological Time Scale.

3. The Time Scale has four major divisions.
The largest divisions are referred to as eons.
There have been two eons, the Precambrian, and the Phanerozoic
Eons extend for hundreds of millions to billions of years.

4. The Precambrian represents the first 85% of Earth history.
The Precambrian is essentially devoid of a fossil record for several reasons:
Plants and animals were small, with no hard parts needed for preservation as fossils.
Most rocks formed during that period are non-sedimentary.
Igneous and metamorphic rocks have been distorted and transformed by heat and pressure, destroying fossil evidence.

5. The Precambrian has unique subdivisions
There are several systems for describing the Precambrian eon.
The fossil record is very sparse during most of Earth history
Life caused profound changes in the atmosphere and oceans, which are captured in rocks and minerals formed during this time.

6. History and Evolution of Earth’s Atmosphere
Earth was born 4.55 million years ago in the nebula that created the sun.
For 500 million years, the interior of the earth was solid, composed of mostly iron and silicates with small amounts of other elements, some radioactive.
As millions of years passed, Earth heated up and gradually melted the solid materials.
Iron melted first – because of its high density, it sank toward the center, forcing up other material found there.

7. Early Earth Surface
Earth’s surface was in turmoil; many volcanoes, lava flows.
As Earth cooled, a stable crust developed.
Oceans formed soon after Earth’s crust cooled.
The primordial atmosphere was produced by outgassing volcanoes.
Volcanic gases consist of H2O, CO2, N2, CH4 and other trace gases.
Our current atmosphere evolved over billions of years (secondary atmosphere)
O2 levels were negligible for most of Earth history – the rise of plants took a long time to produce our modern atmosphere

8. The Phanaerozoic Eon is subdivided into eras
Eras extend for several hundred million years
Marked by profound, abrupt changes in the fossil record.
Major mass extinctions at the end of the Paleozoic and Mesozoic
Paleozoic 8.5% of Earth history
Mesozoic 3.5% of Earth history
Cenozoic 1.4% of Earth history

9. The Cambrian Explosion

10. The Paleozoic Era

12. Lesser extinction events are marked by periods
The Paleozoic, the Mesozoic, and the Cenzoic eras are divided into periods – the most common way of referring to chunks of geological time.

13. Periods range from 40 to 80 million years in length
The ESRT have short descriptions of common extinct organisms that lived during each period.
The larger extinction events are shown in brackets in the Life on Earth column.

14. Periods are subdivided into epochs
Currently we are living in the Holocene epoch.
A new epoch has been proposed: the anthropocene, as a result of dramatic increases in the rate of extinction of plants and animals.
The conditions of the Eocene were much warmer than today – climate change projections are compared to this time.

15. Geological time is based on the fossil record
Fossils provide evidence that a great many kinds of animals and plants have lived on Earth in the past under a variety of conditions.
Most organisms (>99%) have become extinct; only a tiny fraction of these are found as fossils.
Two conditions seem to be necessary for fossil formation:
Organisms must be buried soon after death
Animals must have hard shells, bones, or teeth

16. Paleontology: Studying Fossils
Paleontologists use the principle of uniformitarianism to study conditions under which organisms live and develop, and compare them to extinct fossil species.
From this comparison, past environments can be inferred.
The geographic distribution of both present-day and prehistoric plants and animals is closely controlled by climate – temperature, food availability, and water.

17. Time Distribution of Fossils
Major phyla of plants and animals are shown on the ESRT.

18. Geologic History of New York State
Event
Period, mya
Insects first appeared
Extinction of trilobytes
Catskill Delta forms
First coral reefs formed
Earliest fish appeared
Dinosaur extinction
First Flowering plants
Grasses appear
Earliest mammals (placental animals)
Adirondacks uplifted
The mid-Atlantic rift begins to form
NY in subduction zone
First animals with shells
First land plants/animals
Supercontinent (Pangea)
Fill in the following table:

19. New York is home to many fine specimens of Phacops.
Using your ESRT, find the following:
The period of time in which it lived
A landscape region in New York where it may be found.

23. The Catskill Delta was deposited during the Devonian Period (416-359 mya)
An orogeny is a period of mountain building.
The collision of two tectonic plates produced the Acadian Orogeny.

24. Former Coral Reef in Western NY
Note that the precursors to North America were close to the equator at the time.
Former Coral Reef in Western NY