Beingging of Life

Where does life come from?

Have you ever walked out after a thunderstorm and found earthworms all over the sidewalk? Earthworms have been found in large numbers after rainstorms for hundreds of years. It's no wonder that people used to think the earthworms had fallen from the sky when it rained. It was a logical conclusion based on repeated experience. But was it true? Jan Baptist van Helmont wrote a recipe for making mice by placing grain in a corner and covering it with rags. For much of history, people believed that living things came from non-living matter, an idea called the theory of spontaneous generation.


 People also believed that maggots came from decaying meat. In 1668, Francesco Redi, an Italian doctor, conducted one of the first controlled experiments in science. He showed that maggots hatch from eggs that flies had laid on meat, and not from the meat itself.

 In the late 1700s, Lazzaro Spallanzani designed an experiment to show that tiny organisms came from other tiny organisms in the air. He boiled broth in two flasks, sealed one, and left the other one open to the air. The open flask became cloudy with organisms. The sealed flask developed no organisms. People believed Spallanzani had destroyed a "vital force" when he boiled the broth.

It was not until the mid-1800s that Louis Pasteur, a French chemist, showed conclusively that living things do not come from nonliving materials. In the experiment illustrated in Figure 1-7, Pasteur boiled broth in flasks with long, curved necks. The broth became contaminated only when dust that had collect-ed in the curved neck of one flask was allowed to mix with the broth. The work of Redi, Spallanzani, Pasteur, and others provided enough evidence finally to disprove the theory of spontaneous generation. It was replaced with bio-genesis, the theory that living things come only from other living things.

What are the origins of living things?

If living things can come only from other living things, how then did life on Earth begin? Scientists hypothesize that about 5 billion years ago, the solar system was a whirling mass of gas and dust. The sun and planets formed from this mass. Our planet is thought to be about 4.6 billion years old. Rocks found in Australia that are more than 3.5 billion years old contain fossils of once living organisms. 

 One hypothesis on the origin of life was proposed by Alexander I. Oparin, a Russian scientist. Oparin suggested that the atmosphere of early Earth was made up of gases similar to ammonia, hydrogen, methane, and water vapor. No free oxygen was present as it is today. Energy from lightning, and ultraviolet rays from the sun, helped these early gases to combine. The gases formed the chemical compounds of which living things are made. Oparin suggested that as the compounds were formed, they fell into hot seas. Over a period of time, the chemical compounds in the seas formed new and more complex compounds. Eventually, the complex compounds were able to copy themselves and make use of other chemicals for energy and food. 

Ever since Oparin formed his hypothesis, other scientists have been testing it. In 1953, an American scientist, Stanley L. Miller, set up an experiment using the chemicals suggested in Oparin's hypothesis. Electrical sparks were sent through the mixture of chemicals. At the end of a week, new substances, similar to amino acids that are found in all living things, had formed. This showed that substances present in living things could come from nonliving materials in the environment. It did not prove that life was formed in this way. Evidence suggests that life was formed from nonliving matter sometime between 4.6 billion and 3.5 billion years ago. However, scientists are still investigating where the first life came from.