The Timeline of Evolution

The History of Life on Earth: 

The History of Life on Earth How Did Life Begin on Earth

Objectives: 

Objectives Summarize how radioisotope can be used to determine the age of the Earth. Compare two models that describe how the chemicals of life originated. Describe how cellular organization might have begun. Recognize the importance that a mechanism for heredity has to the development of life.

The Age of the Earth: 

The Age of the Earth Scientists believe the Earth to be approximately 4.5 billion years old. They speculate that it was once a fiery ball of molten rock that cooled into a solid crust. Water vapor in the atmosphere condensed to form the vast oceans of the planet. Most scientists believe that life began in these oceans.

Measuring the Age of the Earth: 

Measuring the Age of the Earth Scientists estimate the age of the Earth through a process called radiometric dating. Radiometric Dating: A process of measuring the age of an object by determining its concentration of certain radioactive isotopes, particularly Carbon 14. The time it takes these isotopes to breakdown into their more stable forms is known. By comparing the percentage of material that is still in a radioactive form and comparing the half-life of the material to the volume remaining, an estimate of the age of the object may be obtained.

Formation of the Chemicals of Life: 

Formation of the Chemicals of Life Many scientists believe that life began as a random series of chemical and physical processes. It is thought that life began when molecules of non-living chemicals reacted chemically during the first billion years of Earth’s history. The reactions produced many simple organic compounds which combined under the influence of volcanic and solar energy, to produce more and more complex molecules

Evolutionary Models: 

Evolutionary Models Primordial Soup: Russian scientist A.I. Oparin and British scientist J.B.S. Haldane both suggested that Earth’s vast oceans were once filled with many different organic molecules like meat and vegetables in a soup. Oparin and Haldane theorized that these molecules spontaneously formed in chemical reactions powered by lightening, volcanoes, and solar radiation. In 1953 the theory was tested by Stanley Miller. He attempted to recreate the primordial soup and appeared to create complex organic molecules using electric sparks as an energy source.

Reevaluation of Miller’s Model: 

Reevaluation of Miller’s Model Later it was determined that the Earth did not, at that time, possess an ozone layer in the atmosphere. The ozone layer protects the Earth from much of the Sun’s harmful Ultraviolet radiation. Without this layer of protection, the sun’s rays would have destroyed any methane or ammonia or other complex molecules that might possibly be created in the primordial soup.

The Bubble Model: 

The Bubble Model If the gasses necessary for life to evolve had not existed in the atmosphere, where did they come from? In 1986, a geophysicist name Louis Lerman suggested that these gasses were trapped in bubbles on the surface of the ocean and that life began here. Step 1: Methane, ammonia, and other gasses erupt from the ocean floor and are trapped in bubbles on the surface.

The Bubble Model: 

The Bubble Model Step 2: Inside the bubbles, the gasses needed to create amino acids and proteins might have been protected from damaging UV rays. Chemical reactions would have taken place faster in the bubbles (where the gasses were more concentrated) than in the open primordial soup. Step 3: Bubbles rose to the surface and burst releasing simple organic molecules into the air.

The Bubble Model: 

The Bubble Model Step 4: Carried upward by the wind, the simple organic molecules might have been exposed to UV radiation and lightening which provided the energy needed for further reactions. Step 5: More complex molecules could be formed as further reactions occurred. These might fall back into the ocean and start another cycle of the process