Origin of Life: Earth's Early Conditions and Theories

The Early Earth

The Earth formed approximately 4,600 million years ago, with temperatures exceeding today's by hundreds of degrees. These high temperatures were partly due to meteor impacts. The Earth's rock melted, and heavier elements like iron and nickel sank to the planet's center. This began a slow cooling and solidification of the outer layer. Elements combined to form various compounds. Almost all oxygen combined with hydrogen to form water, with carbon to form carbon dioxide, and with other elements (methane and carbon monoxide) to form minerals. After millions of years, the temperature dropped below 100°C, and steam clouds condensed, raining for hundreds of years to form slightly salty oceans.

Early Atmosphere

Scientists believe Earth's early atmosphere was very different from today's. It likely consisted of hydrogen (H₂), carbon dioxide (CO₂), methane (CH₄), ammonia (NH₃), nitrogen (N₂), and water vapor, among other gases. There was virtually no oxygen (O₂) or ozone (O₃), which absorbs solar ultraviolet radiation.

Oparin-Haldane: Coacervates Theory

Between 1920 and 1930, Oparin and Haldane proposed a theory on the origin of life: "Millions of years ago, chemical reactions, favored by early Earth's conditions, generated organic matter from inorganic matter, which was needed to form living beings. This process is called prebiotic synthesis."

Miller-Urey Experiment

In 1953, a heated, closed device containing a gas mixture of ammonia (NH₃), methane (CH₄), hydrogen (H₂), and water vapor (all inorganic compounds) produced a variety of organic compounds, including amino acids (the building blocks of proteins) and urea.

1. The gas mixture was introduced into a container simulating the early atmosphere.
2. The mixture was subjected to electric shocks while water was boiled, forcing steam to circulate the gas.
3. After a week, organic compounds had formed.

The Theory of Panspermia (Universal Seed)

This theory suggests that the first organisms originated outside Earth and arrived on an asteroid.

Spontaneous Generation

In the mid-nineteenth century, this theory was based on direct observation of larvae appearing on decaying organic matter, worms in mud, and mildew in damp places. Aristotle was a strong advocate of this theory, which persisted well into the Renaissance (15th-16th centuries).

Redi's Experiment

In 1668, Redi conducted the first experiments to demonstrate the fallacy of spontaneous generation. He placed pieces of meat in three identical containers:

• The first bottle was sealed.
• The second bottle was covered with gauze.
• The third bottle was left open.

After some time, he observed that the first bottle had no worms, even though the meat was rotten and smelly. The second bottle had fly eggs on the gauze. The meat in the third bottle had plenty of larvae and flies. This experiment began to show the falsity of the theory of spontaneous generation.

Pasteur's Contribution

In 1861, Pasteur overcame the objection of the absence of air and conclusively disproved the idea of spontaneous generation. He demonstrated that microorganisms originate from other microorganisms.

Van Helmont's View

In 1667, Van Helmont stated: "Lice, ticks, fleas, and worms emerge from our guts and excrement. If we place wheat and a sweaty shirt in a wide-mouth container, after 21 days, the fumes from the wheat bran will transmute into mice. These mice can be viewed from both sexes and across to others who have emerged as usual..." He proposed a recipe for the spontaneous generation of mice and was in favor of Spontaneous Generation.