Origin of Life


Origin of Organic Molecules

  • Miller Urey Experiment 1953 and 1958

    • In 1953 they created an experiment where they simulated the conditions they believed to be on Early Earth- hydrogen, ammonia and methane with electrodes to simulate lightning (a primordial soup)

    • 5 organic molecules were formed

    • However heavily criticised as the gases used didn’t represent all the gases found in the atmosphere and methionine wasn’t found which is the starter amino acid to all protein

1 of 11

Origin of Organic Molecules

  • Molecular Panspermia- suggested organic molecules originated in space

    • Spectral analysis showed glycine is present in nebulas, similarly meteorites and comets contain amino acids.

    • 4 billion years ago earth was showered with comets- the impact could have polymerised certain amino acids into polypeptides

  • Sydney Fox- showed amino acids could polymerise and form proteinoid spheres

2 of 11

Origin of Organic Molecules

  • Volcanoes and Deep Ocean hydrothermal vents- probably where first life formed

    • This is because hydrogen sulphide gas could be used to make sulfur containing amino acids and produced a warm environment for reactions to take place

3 of 11

Origin of Organic Molecules

  • Volcanoes and Deep Ocean Hydrothermal Jets

    • This is probably where first life was formed

    • This is because it would provide hydrogen sulfide gas which is a source of sulfur that could be used to make sulfur containing amino acids and a warm environment for chemical reactions

  • Endosymbiotic Theory

    • A prokaryote cell absorbed another smaller cell but instead of being digested the cells live symbiotically

    • Believe a photosynthetic cell was absorbed therefore mitochondria were created

4 of 11

Origin of Organic Molecules

  • These engulfed cells are thought to:

    • Have double membranes

    • Their own DNA

    • Can perform independent protein synthesis using small ribosomes

    • Can replicate themselves within the host

5 of 11

Evolution and Natural Selection

  • Genes are special sequences of As, Ts, Gs and Cs in DNA that encode for little cell machines called proteins. Each gene is unique whose protein does a unique job.

    • Variation in organisms is due to variations in the sequences of As,Ts,Gs and Cs

  • Ionising radiation and chemicals can increase the rate of mutations in our DNA. Mostly, these are corrected by DNA repair enzymes. However, sometime mistakes occur and create permanent mutations that can affect proteins. Some mutations in DNA are harmful but most are neutral and a few are beneficial. Some are both harmful and beneficial such as the cystic fibrosis allele which can cause resistance to cholera, but also cause cystic fibrosis

6 of 11

Evolution and Natural Selection

Basis of Natural Selection:

  1. The environment is a changing place

  2. Variation can influence whether organisms are reproductively successful in certain environments

  3. If successful, the organisms pass on their genes/ to the next generation

  4. That particular variety will become more prominent in the population.

Natural selection involves interactions between organisms and their environment

Evolution is measured by the changes in populations.

7 of 11

Evolution and Natural Selection

Natural selection eventually leads to evolution as characters of the population changes. Eventually, these changes are so great the population becomes a new species that are so different they can’t reproduce with individuals from the older species.

Charles Darwin and Alfred Russel Wallace came up with this hypothesis

Darwin supported the idea that organisms developed in one place and then migrated around the earth.

Geographical Isolation- areas become geographically isolated which means individuals in the same species can’t interbreed and therefore lose certain variations depending on their environment

8 of 11

Evolution and Natural Selection

Artificial selection- proves that species can change over time with selective breeding.

Homologous Anatomy (species with similar anatomy) can show species are closely related however, there are unrelated species with similar structures (analogous structures) and are examples of convergent evolution.

Cladistics- biological classification of organisms, based on shared characteristics. These characteristics can be traced back to the group’s common ancestor.

A Clade- a grouping that includes a common ancestor and all the descendants  of that ancestor.

9 of 11


We find common ancestors because we can sequence the As, Gs, Ts, and Cs of mitochondrial DNA from different species. DNA mutates at a fairly constant rate (we can use this as a molecular clock). The degree of differences between mitochondrial DNA from different species shows how long ago they shared an ancient ancestor.

mtDNA and Y chromosome analysis show that humans share a common ancestor that came from Africa about 170,000 years ago.

We find out how old fossils are through radio-dating. By measuring how much of a radioactive material is left in a something we can find out how old it is. A half life is the time it takes to reduce the number by a half.

10 of 11


Radio-dating fossils shows the existence of a human-like ancestor that was bipedal about 4.4 million years ago.

The central position of the foramen magnum indicates if the organism walks on its two hind legs (bipedal).

Development of tool making, hunting skills and language have contributed to survival and natural selection.

Human Ancestors :Australopithecus, Homo habilis, Homo erectus,Homo neanderthalus, Homo neanderthalalensis ( ‘Neanderthal man’) ,Homo sapiens (modern humans)

11 of 11


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Origin of Life resources »