The Origin of Life Section 4 of what is life?

The atmosphere of Early Earth—What was it like?

Early Earth had very little oxygen in the air.Scientists believe that the conditions of the

atmosphere in Earth’s beginning were very different than they are today.

Abundant gases in the atmosphere were nitrogen, water vapor, carbon dioxide, and methane.

Today the abundant gases are nitrogen and oxygen.

The first life forms resembled the “archaea” of today.

The earliest life forms appeared on Earth some time between 3.5 and 4.0 billion years ago.

Without oxygen many of today’s organisms could not have survived in the beginning.

The traits of these first life forms were: did not need oxygen, unicellular and lived in the oceans.

So, what are “archaea” life forms? They live in extreme conditions like polar ice caps, hot springs and the mud of ocean bottoms.

Stanley Miller & Harold Urey gave us the first clues for this thought.

How did the early life forms arise?Redi and Pasteur showed that living things

do not spontaneously arise. However, scientists reason that the first life forms probably did arise from nonliving materials!!!!

Then they sent an electric current through the mixture = lightning.

In 1953 Miller (student) and Urey (advisor) designed an experiment.

They recreated the conditions of early Earth by placing water (ocean) and a mixture of gases (atmosphere) into a flask.

They kept the oxygen and unicellular organisms out of the mixture.

The setup was leftfor a week and atthe week’s endsome small chemical units that could form proteins were found!! They wereamino acids-thebuilding blocks ofproteins.

The first cells:More experiments similar to Urey and Miller were

performed and some of those came up with the units that make up carbohydrates and nucleic acids. This led scientists to this hypothesis:◦The small chemical units of life formed gradually

over millions of years in Earth’s waters. Some of the chemical units joined to form the large chemical building blocks found in cells. Eventually, some of the large chemicals joined together and became the forerunners of the first cells.

Therefore, fossil evidence supports the idea that cells existed 3.4-3.5 bya!

Fossil evidence:A fossil is a trace of an ancient organism that has

been preserved in rock or another substance.

Fossils have been found that appear to have archaea-like organisms in them. The dates on these fossils are 3.4-3.5 billion years old!

The first cells did not need oxygen. They were most likely heterotrophs that used chemicals in their surroundings for energy.

These cells grew and reproduced and as their numbers grew the amount of chemicals available decreased.(remember supply and demand = competition)

Later on the cells may have developed the ability to make their own food. This would be the autotrophs.

As autotrophs made their own food they produced oxygen as a waste product. As autotrophs thrived the oxygen then began to accumulate in the atmosphere.

Over hundreds of millions of years the oxygen increased to its current level.

Models, experiments, and fossil evidence will continue to be looked at for better and better answers to satisfy mankind’s curiosity.

Many scientist are continuing to explore the question of “HOW” and “WHERE” life first arose on Earth.

Miller and Urey did not PROVE how life first appeared—it is only a hypothesis.

NO ONE will ever know for certain how and when life appeared on Earth.

Will scientists continue to look? YES

Study, study, study for your test!

The End