Origin of Life What do you think the first organism was like?

Early Earth Early Earth was formed about 4.6 billion years ago and was very different than earth today. How do you think it might have been different?

Early Earth The atmosphere was very different than it is now, containing little or no oxygen. Earth was too hot for liquid water. Once the surface cooled enough for rocks to form, the surface was covered with volcanic activity. About 4 billion years ago

Early Earth About 3.8 billion years ago the Earth cooled enough for liquid water to remain. Thunderstorms drenched the planet and oceans covered most of the surface.

Could the building blocks of life have formed under these extreme conditions? In the 1950’s Stanley Miller and Harold Urey tried to simulate the conditions of early Earth. They showed how several amino acids could be created under those conditions.

Miller and Urey’s Experiment They passed sparks (representing lightening) through a mixture of hydrogen, methane, ammonia, and water (representing the atmosphere)

Miller and Urey showed that the mixtures of organic compounds necessary for life could have arisen on primitive earth! Miller continued to perform experiments like the one in the 1950s. In 1995, he was able to produce cytosine and uracil, two of the bases found in RNA.

Hypothesis of the Origin of Life The leap from a mixture of organic molecules to a living cell is large.

What kinds of characteristics do living things have? They appear to: - ingest things - grow - reproduce

Hypothesis of the Origin of Life Experiments have shown that under the conditions of early Earth, small RNA sequences could have formed and replicated on their own. This could have created a simple RNA-based form of life from which the DNA system could have evolved.

Hypothesis of Origin of Life How certain do you think this hypothesis is? Do you think it will ever be changed? Do you think it will be changed during your lifetime?

Origin of Life Evidence indicates that about 200-300 million years after the accumulation of liquid water on Earth, cells similar to modern bacteria were common.

Changing Earth Photosynthetic bacteria became common and oxygen began to accumulate in the atmosphere and the ozone layer formed.

The rise in oxygen caused some life forms to go extinct, while others evolved ways to use oxygen for respiration. More diverse species of life began to develop….

Hypothesis of Origin of Eukaryotic Cells-Endosymbiotic Theory Prokaryotic cells began to evolve internal cell membranes- this was the ancestor to eukaryotic cells. Smaller prokaryotes began living inside this ancestor and over time it became an interdependent relationship. What does this mean?

Endosymbiotic Theory One group which entered the cell had the ability to use oxygen to generate ATP. These evolved into mitochondria. Another group of prokaryotes which carried out photosynthesis evolved into chloroplasts.

Evidence for Endosymbiotic Theory Mitochondria and chloroplasts have many characteristics of free living bacteria: 1- contain DNA similar to bacterial DNA 2- have ribosomes of similar size and structure to those of bacteria 3- reproduce by binary fission like bacteria

Some eukaryotes began to reproduce sexually. What do you remember about sexual reproduction? How is it advantageous for organisms?

VARIATION! Sexual Reproduction results in increased variation in living organisms, increasing the rate of evolution. This is what jumpstarted species diversification on earth.