Evolution: Origins of Life

We know that there is a great variety of living organisms in our biosphere.

All living organism also interact with one another as well as with abiotic factors.

We are all composed of the 4 same biomolecules

How did we get to be a planet with such rich biodiversity?

I. Theories on the Origins of Life

• A. People’s idea about where some living things come from have changed throughout history.

• B. Prior theories:– 1. Recipe for Bees (Aristotle)– 2. Spontaneous Generation(disproved by Francesco Redi)– 3. Pasteur’s TestLiving things come from living things

II. Changing Theories

• A. Redi’s experiment:– 1. Controlled jars – open meat jars, maggots appeared– 2. Tested jars (covered in gauze) – maggots did not

appear

• B. Redi’s experiment scientists understood that life could not rise from nonliving matter. (abiogenesis)

II. Changing Theories

• C. Pasteur’s Experiment:– 1. Boiled broth that was kept open to air through a

round neck did not have any microorganisms living in it– 2. If the flask with broth was broken living things would

begin to appear

• D. Pasteur’s experiment allowed scientists to begin to understand that living things only come from other living things. (biogenesis)

III. Conditions of Early Earth

• A. Some scientists still believe that spontaneous generation of life occurred once but was now impossible because the conditions found on early Earth have changed.

• B. Several scientists began experiments to replicate ancient Earth & gain support for the “primordial soup” theory. Oparin & Haldane proposed such theories.

• C. Ancient Earth:– 1. Major volcanic eruptions– 2. Hundreds of meteor showers– 3. Constant lightning storms– 4. Atmosphere composed of carbon dioxide, nitrogen,

hydrogen sulfide & sulfur dioxide– 5. NO OXYGEN!!

IV. Miller-Urey Experiment (1953)

• A. Mixture of water, hydrogen, methane, and ammonia was cycled through an apparatus that delivered electrical sparks to the mixture.

• B. At the end about 10% to 15% of the carbon in the system was now in the form of a mixture of organic compounds, including something similar to amino acids, which are the building blocks of proteins.

Life on Earth came from Mars

V. First Life

• A. All living things are composed of cells; the 1st life form was an organism very similar to bacteria.

• B. First life forms were composed of prokaryotic cells– 1. Prokaryotic cells – cells with no nucleus

VI. Endosymbiosis• A. Scientists theorize that

eukaryotic cells originated through symbiosis between micro-organisms. – 1. In other words: organelles were

taken inside another cell and became part of the cell

• B. Example:– 1. An animal cell’s mitochondria

was originally a proteobacteria – 2. A plant cell’s chloroplasts was a

cell taking up a cyanobacteria