LE1 – 05 - Origin of Life on Earth – Theories & Experiments

Origin of Life How old is the Earth? How did the Earth form? How did life form on Earth? When and what type of life started on our planet?

Beginning of the Solar System About 5 billion years ago, our solar system was a swirling mass of gas and dust which collapsed inward to form the sun. Planets are thought to have been formed from repeated collisions with space debris.

FORMATION of the EARTH The Earth grew larger as more debris collided with it which occurred during its 400 million year long period. With each collision the Earth grew in size and also with thermal energy. Using Radioactive Dating Techniques, of zircon crystals, Scientists have estimated that the earth is about 4.6 billion years old (give or take a couple billion years.)

Theory of the Origin of Life Twenty years after Pasteur’s experiment, Thomas Henry Huxley first used the term biogenesis. Biogenesis is all living things arise only from other living things of the same type. BUT where did the first Life come from?

Where did the first living things come from? Scientists agreed that the following must occur for life to come into being: The formation of simple organic compounds (eg. Amino Acids) important to life. The formation of complex organic compounds (eg. Proteins). The concentration and enclosure of these organic compounds (eg. Cell membrane). The linking of chemical reactions involved in growth (eg. Metabolism).

Heterotroph Hypothesis In the 1930’s, A.I. Oparin, a Russian biochemist and John Haldane, an American biochemist. Presented a hypothesis to explain how the first living things might have developed. This theory was called the Heterotroph Hypothesis.

Heterotroph Hypothesis (cont) These gases formed the atmosphere of the primitive earth. H2 (Hydrogen gas) NH4 (Ammonia) CH4 (Methane) CO2 (Carbon Dioxide) Water Vapor N2 (Nitrogen Gas) H2S (Hydrogen sulfide) Volcanoes released gases up into the air with steam (water vapor). Eventually, the steam condensed and collected and became the oceans of the primitive earth.

Heterotroph Hypothesis (cont.) Primitive Earth

Heterotroph Hypothesis (cont.) Modern Earth

The Experiments – Part I Stanley Miller and Harold Urey (1953) created an experiment to test the Heterotrophy Hypothesis. electrodes heat source amino acids water “atmosphere” “ocean”

Section 2 The History of Life

After his experiment he found numerous organic compounds including amino acids. Although, amino acids are the building blocks of proteins, Miller had not created life. They did show that conditions like those on early earth could produce chemicals present in living things.

Other experiments have shown that nucleotides (bases for DNA) sugars and other amino acids can be formed from this primordial soup.

PART II – Concentration and Enclosure Experiments have shown that proteins clump together to form microscopic droplets (coacervates and microspheres) Coacervates and microspheres bear a resemblance to living cells (Cell membranes).

a) All are set off from the environment by a membrane like boundary. b) All can take up certain substances from their surroundings. c) Certain chemical reactions can take place more easily inside these structures than they can in water. d) Coacervates can grow and microspheres can bud.

DNA has been enclosed in membranes in the lab. This was a major step in the development of life because once DNA was separated from the environment by some kind of boundary, it would be protected and might be able to carry out the precise reactions of replication

Part III – Evolution & Reproduction As lifelike as coacervates and microspheres appear, they lack the complexity of living things. They can neither maintain stable growth, nor reproduce. They also cannot obtain energy from substances in the environment. But over time, these capabilities may have developed. So far, no experiments account for the assembling of biomolecules into a living, replicating cell.

IN SUMMARY: Evidence suggests that sometime between 4.6 and 3.8 billion years ago, life arose on earth, generated from non-living matter. Such spontaneous generation could not occur on earth today. The atmosphere of the young earth lacked oxygen gas which would have destroyed organic compounds by the chemical process called oxidation. Thus, the unique circumstances under which life spontaneously arose are no longer present on earth.

Single-celled organisms existed approximately 3 Single-celled organisms existed approximately 3.8 billion years ago… so what were their characteristics?

The first life was prokaryotic cells (bacteria). The oldest known fossils are a group of marine cyanobacteria. prokaryotic cells they are photosynthetic added oxygen to atmosphere (their waste product) deposited minerals (nitrogen)

Fossils of Stromatolites (colonies of cyanobacteria; aquatic) provide evidence of early colonies of life. *Add this into your notes

Microbes have changed the physical and chemical composition of Earth. With the release of oxygen gas from the bacteria, it is hypothesized that it formed into our now Ozone layer. The ozone layer protects organisms, from majority of the Ultraviolet radiation that comes from the sun.

Endosymbiote Hypothesis Proposed in 1966 by Lynn Margulis.

A theory about how prokaryotes may have come to live inside eukaryotic cells. This would allow the prokaryote to have protection inside the eukaryotic cell. In turn, the eukaryotic cell would be provided extra energy and food from the prokaryote.

Endosymbiote Hypothesis Endosymbiosis is a relationship in which one organism lives within the body of another. The bacteria eventually evolved into the mitochondria and chloroplasts of eukaryotic cells.