The Origin of Life
The Atmosphere of Early Earth
On early Earth there was very little oxygen in the air
"On ancient Earth, nitrogen, water vapor, carbon dioxide, and methane were probably the most abundant gases in the atmosphere"
Today, the gases in the atmosphere are mainly only nitrogen and oxygen
Life on Early Earth
Today, we think that early life first appeared on Earth around 3.5 to 4.0 billion years ago
Most of today's organisms would not survive on early Earth because there was no oxygen in the air
We can never be sure what the first life forms looked like but scientists have made many guesses
Early life forms characteristics: didn't need oxygen to survive, was probably unicellular, probably lived on the oceans, may have resembled the arcaea that today live in extreme conditions
Modeling Conditions on Early Earth
Scientist still struggle with explaining how early life forms for formed
"Although Redi and Pasteur showed that living things do not spontaneously arise on today's Earth, scientists reason the first life forms probably did arise from nonliving materials"
In 1953, Stanley Miller and his adviser Harold Urey, designed an experiment that recreated early Earth environments and played around with the chemical balance until they found that proteins could form, and they are one of the building blocks of life
The First Cells
"Scientists hypothesize that the small chemical units of life formed gradually over millions of years in Earth's water; some of these chemical units joined to form the large chemical building blocks found in cells; eventually, some these large chemicals joined together and became the forerunners of the first cells"
Many scientists think that life on early Earth formed from small chemical units
Support From Fossil Evidence
FOSSIL: "a trace of of an ancient organism that has been preserved in rock or another substance"
Ancient fossils have been dated from 3.4 to 3.5 billion years old; these then can show us that cells must have existed back then
The first organisms did not need oxygen to survive and were probably heterotrophs, using chemicals around them to gain energy
As cells grew and reproduced, the amount of them increased, then causing the chemicals around them to decrease
A while later some cells may have developed the ability to make their own food, and are now the ancestors to autotrophs; in the process of making their own food, they produced oxygen, and it accumulated to today's level over hundreds of million of years
Unanswered Questions
Experiments that have been done and are being done cannot prove how life first came to Earth; they can only help us make hypotheses
While we may never know how life first came to be, scientists continue to explore the area of question