The Origin Life
The Atmosphere of Early Earth
The First Cells
On ancient Earth, nitrogen, water vapor, carbon dioxide, and methane were probably the most abundant gasses in the atmosphere.
Life on Early Earth
People made hypothesis that the early life forms did not need oxygen to live
They were probably unicellular.
And they probably lived in oceans.
The first organisms resembled the first archaea that live today in extreme environments, such as polar ice caps, hot springs, and the mud of ocean bottoms.
Modeling Conditions on Early Earth
Although Redi and Pastuer showed that living things do not spontaneously arise on today's Earth, scientists reason that the first life forms probably did arise on nonliving materials.
Scientists hypothesize that 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
A fossil is a trace of an ancient organism that has been preserved in a rock or another substance
The first cells didn't need oxygen to survive
At some point much later, some of the cells may have developed the ability to make their own food
As the autotrophs thrived, oxygen accumulated in Earth's atmosphere.
Over hundreds of millions of years, the amount of oxygen increased to its current level
Unanswered Questions
Such experiments can only test hypothesis about how life forms could have arisen.