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

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)

CAMBRIAN PERIOD542-488 mya

ORDOVICIAN PERIOD488-444 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.

During this molten phase, Earth interior zones became established as denser material settled to the

Earth’s core.

Hundreds of millions of years after its creation, the Earth cooled enough to develop a

crust.

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.

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.

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.

Landforms became predominant amongst the oceans. Sophisticated life forms continues to evolve as oxygen

levels continued to rise including multicellular organisms.

Evolution of LifeThe 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.

At times, the evolutionary change of

groups of organisms can be recorded in the

rock record.

Horses have

evolved over the past 55 million years.

Fossils of horses have

shown a change in size, tooth shape and leg design.

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).

Why are fossils from the past found in New York very different from the organisms that live there today?

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