The early earth

The Big Bang!
The universe is believed to have formed out of an explosion of a giant concentration of matter with a “big bang”. The “big bang” theory postulates that at the beginning all the matter was compressed into one big hot mass, which exploded violently and then expanded to give rise to stars, galaxies and planets. This occurred about 10 to 20 billion years ago.

However, our solar system, to which the earth belongs, is only 4.5 billion years old. It was probably formed from a huge spinning cloud of gas and dust left by a dying star, called the solar nebular. It is believed that the hot centre of the cloud became the sun while the outer layers formed the planets.

The earth’s primitive atmosphere might have consisted of hydrogen, which eventually escaped because the earth’s gravity was too weak to hold it. It took millions of years for the earth to cool and during this time it experienced intense volcanic eruptions which released into the air gases, including nitrogen, ammonia, carbon monoxide, methane, carbon dioxide and water vapour. There is no evidence that oxygen was present at this time.

As the temperature later cooled to below 100 ⁰ C water vapour condensed and fell as rain, filling depressions and craters on the earth’s surface which became lakes and oceans.

Origin of Life

Theories that try to explain the origin of life and indeed the universe exist in every society. While many people believe there must be some supernatural power that created the universe and life there is no agreement as to the nature of the supernatural power.

Other people contend that life had no divine beginning and that it has no beginning and no end. These two theories are impossible to prove and both groups must be prepared to tolerate each other’s views.

The major known theories about the origin of life on earth are:

1. Special creation

2. Spontaneous generation

3. Steady state

4. Cosmozoan

5. Biochemical evolution

Special Creation

Christians believe that the universe was created in six days by a superbeing they refer to as God. Some even believe that the world is only 6000 years old. Even among the Christians themselves, there is no unanimity on the literal interpretation of the bible. Rather than believing that the universe and everything that is in it was created in six days, some Christians explain that a day in God’s reckoning is a long time.

Spontaneous Generation

Spontaneous generation or abiogenesis theory says that life arose from nothing. For example, maggots normally seen on a decomposing body were believed to have arisen spontaneously. However, it took the work of several scientists to disprove the abiogenesis theory and show that life could only arise from pre-existing life. This is known as biogenesis.

Among these scientists were Lazzaro Spallanzani and Louis Pasteur. Lazzaro Spallanzani (1765) boiled animal and vegetable soup for several hours then sealed the container. When he examined the mixture several days later, he found no sign of life and concluded that the heat had destroyed all the forms of living organisms originally present in the container.

In 1862, Pasteur reported the result of an experiment, which showed that life could only arise from another life. Pasteur had taken identical flasks and filled them with identical nutrient solutions, which he heated to kill any bacteria present, then left the flasks undisturbed for some weeks. On examining the flasks, he detected germs in the short-necked flask. For the long necked flask, germs were trapped in a film of vapour within the bend. He concluded the bacteria were present in the air.

 Steady State

This theory argues that the earth, animals and plants have no origin and have always existed in a steady state. There are only occasional changes, such as increases or reductions in numbers.

Cosmozoan Theory

The Cosmozoan theory contends that life did not originate from the earth but had an extraterrestrial origin and that beings from the space have from time to time, over the millions of years the universe has existed, inhabited the earth and other planets within our solar system and beyond. They cite the flying saucers (UFOs) as an indication that other forms of life exist beyond our planet.

Biochemical Evolution

Scientists believe that life on earth has been evolving gradually over the time and that the current animals and plants evolved originally from chemical reactions that resulted into primitive organisms, such as the single celled protozoa. Through mutation and the effects of the environment, the protozoa evolved into more complex organisms. 

Formation of the First Ingredients of Life

After the big bang and while still cooling, the earth experienced a very turbulent period characterised by strong volcanic, lightning, and ultraviolet radiation forces. These very turbulent and chaotic atmospheric conditions allowed atmospheric gases to react with one another and form simple organic compounds that became the first ingredients of life.

Miller-Urey Experiment

In 1953, Stanley Miller and Harold Urey attempted to create conditions similar to those that existed at the beginning that led to the emergence of life on the earth. They boiled water and a mixture of nitrogen, methane and ammonia. The water vapour and the gases were passed over electric sparks and cooled over a condenser. The sparks were meant to mimic lightning.

They obtained a solution that contained amino acids and nucleic acids. Later studies have confirmed this original finding, suggesting that life might probably have developed from inorganic gases that combined to form the first living organisms. All this happened 3.5 billion years ago

The first fossils of living organisms are 3 billion years old and consist of primitive nonucleated bacteria and algae called prokaryotes. These primitive organisms first appeared in water and produced their own food by converting CO₂ and water into sugar using the solar energy.

6CO₂ + 6H₂O → C₆ H₁₂ O₆ + 6O₂.

The reaction released oxygen into the air. Subsequently, some molecules of oxygen were split by radiation into single (O) atoms. These combined with oxygen to form ozone (O₃). As more ozone was formed, an ozone layer was formed in the atmosphere. This layer blocks harmful ultraviolet radiation from reaching the earth’s surface.

Study Questions

1. Outline and discuss the current concept regarding the origin of life.

2. What does Miller-Urey’s experiment attempt to prove?

3. Describe two experiments that show that life can only arise from pre-existing life.

4. Distinguish between biogenesis and abiogenesis.