Geologic History and the Evolution of Life

Geologic Time Fossil evidence found in rocks allow scientists to determine the age of rocks. Ages of geologic time can be broken down into eons, eras, periods and epochs. The beginning and/or end of each unit of geologic time reflects an important event in the geologic or biologic history of Earth CAMBRIAN PERIOD 542-488 mya For example: The Cambrian Period began 542 mya –a point in Earth’s history where a large number of primitive, soft-bodied animals evolved. The Cambrian Period ended 488 mya when specific invertebrate organisms (brachipods) became the dominant form of animal life. (beginning of the Ordovician Period) ORDOVICIAN PERIOD 488-444 mya

The Evolution of Planet Earth It is estimated that the origin of the Earth can be dated back some 4.6 X 109 years. During this period of time Earth was still very hot and largely molten due to impact events, the decay of radioactive molten material, and gravitational forces within the Earth. Landforms became predominant amongst the oceans. Sophisticated life forms continues to evolve as oxygen levels continued to rise including multicellular organisms. During this molten phase, Earth interior zones became established as denser material settled to the Earth’s core. Nearly 2 billion years later, oxygen levels in the atmosphere continued to rise, oceans increased in size and the development of sedimentary rocks was taking place. Hundreds of millions of years after its creation, the Earth cooled enough to develop a crust. As the Earth continued to cool, water in the atmosphere precipitated to Earth and oceans formed. Primitive life forms (bacteria) began to evolve in these oceans using carbon dioxide as a fuel source and releasing oxygen as a waste product. As the crust cooled, it is inferred that gases trapped within other zones of the Earth began to seep into the atmosphere. This outgassing event lasted millions of years and released nitrogen, water vapor and carbon dioxide.

Horses have evolved over the past 55 million years. Evolution of Life The evolution of life can be seen as sequences of evolutionary events represented in the fossil record. Organic evolution is the process of change over time. Organisms that have favorable, genetic variations that allow them to adapt to environmental changes will survive. These organisms that survive will reproduce and pass these favorable genetic variations to their offspring. Horses have evolved over the past 55 million years. Fossils of horses have shown a change in size, tooth shape and leg design. At times, the evolutionary change of groups of organisms can be recorded in the rock record.

Geologic History of New York Why does New York State not have an entire geologic record of Earth’s history? Due to the theory of plate tectonics, it can be inferred that New York’s position on the Earth now is not what is was in the past. As the North American plate shifted over time. New York state was thrust into higher and lower latitudes from where it is today. Changes in latitude impacted the climate of New York. Different organisms and different environments are associated with different climates. This would explain why there are gaps in the rock record in New York. This would also explain why organisms found in New York today are different from those of the past (fossils). RT = Pg. 3 Why are fossils from the past found in New York very different from the organisms that live there today?