The Origin of Life
Introduction
The Atmosphere of Early Earth
3.5 Billion years ago, the landscape was ragged rocks and little soil and no living things.
It would not have been possible to explore the Earth without an oxygen mast because there was little oxygen in the air. Scientists presume that the conditions on early Earth were very different than they are today.
"On ancient Earth, nitrogen, water vapor, carbon dioxide, and methane were probably the most abundant gasses in the atmosphere. In contrast, the major gasses in the atmosphere today are nitrogen and oxygen."
Life on Early Earth
Evidence suggests that life appeared on Earth between 3.5 and 4 billion years ago, because there was no oxygen in the air to breathe.
No one knows what the first life forms were like. But scientists have made hypotheses about them.
"First, early life forms did not need oxygen to survive. Second, they were probably uni-cellular organisms. Thirdly, they probably lived in the oceans."
The first life forms probably looked like archaea that today, live in extreme environments such as in the bottoms of oceans, hot springs or polar ice caps.
Modeling Conditions on Early Earth
Scientists think that the first life forms most likely arise from non-living materials.
Stanley Milller made the first clues on how organisms might have arisen on Earth.
Stanley Miller and his advisor made an experiment which they recreated the conditions of Early Earth in their labratory.
"They placed water (to represent the ocean) and a mixture of gasses through to compose Earth's early atmosphere into a flask. They were careful to keep oxygen and unicellular organisms out of the mixture. They sent an electric current through this mixture to stimulate lightning."
In a week, the mixture they had made had darkened. In the dark fluid, Miller and Urea (his advisor) discovered some small chemical units that joined together and could form proteins. - one of the building blocks of life.
The First Cells
In the experiment, similar to Miller and Urey, other scientists accomplished in making chemical units to make up carbohydrate s and nucleic acids.
"Scientists hypothesize that the small chemical units of life formed gradually over millions of years in Earth's waters. Some of these chemical units joined to form the large chemical building blocks found in cells. Eventually, some of these large chemicals joined together and became the forerunners of the first cells."
Support From Fossil Evidence
This hypothesis confirms fossil evidence. "A fossil is a trace of an ancient organism that has been preserved in a rock or another su substance."
Scientists found fossils that have been archaea-like organisms.
These old fossils have been dated to be between 3.4 and 35 Billion years old.
The first cells did not need oxygen to survive, they were probably heterotrophes and used chemicals from their surroundings for energy.
When the cells grew, they reproduced, their numbers increased, and the amount of chemicals available to them decreased.
At a point much later, the cells may have developed the ability to make their own food and become autotrophes. "These early ancestors of today's autotrophes had an important effect on the atmosphere. "
When they made their food, they made oxygen as a waste product.
The autotrophes thrived, oxygen built up in the Earth's atmosphere. "Over hundreds of millions of years, the amount of oxygen increased to its current level."
Unanswered Questions
Scientists like Miller and Urey can never prove how life first appeared on the planet Earth. But they can do experiments and do hypotheses on how the life forms could have arisen.
No one will ever know how life first appeared on Earth