The Origin of Life Where did it all begin? Keeping in mind that all of this started a LOOOONG time ago, here’s what we know….

Enduring understanding 1 Enduring understanding 1.D: The origin of life is explained by natural processes. The process of evolution explains the diversity and unity of life. A number of experimental investigations have provided evidence that the conditions early in the Earth’s history provided an environment capable of self-generating complex organic molecules and simple cell-like structures. Ex. Miller-Urey Experiment

Miller-Urey’s experiment coined the “organic soup” model, hypothesized that the primitive atmosphere contained inorganic precursors from which organic molecules could have been synthesized through natural chemical reactions catalyzed by the input of energy from the environment. Basically, the chemicals that build the macromolecules needed for life were already there in the ocean, and the lack of oxygen in the environment combined with energy from severe lightning storms allowed the first living molecules to self assemble and start the chain of events that led to where we are today. Spontaneous generation through chemistry. In turn, these molecules served as monomers (building blocks) for the formation of more complex molecules, including amino acids and nucleotides, that eventually became cells.

Some models suggest that primitive life developed on biogenic surfaces, such as clay, that served as templates and catalysts for assembly of macromolecules. (Again, the perfect chemistry at the perfect time.) Under laboratory conditions, complex polymers and self- replicating molecules (DNA or RNA) can spontaneously assemble. Although, it remains an open question whether the first genetic and self-replicating material was DNA or RNA.

What was the first genetic material? DNA or RNA? The RNA World hypothesis proposes that RNA could have been the earliest genetic material. From the structures of the molecules, it’s logical to conclude individual RNA strands could link up to form DNA molecules in order to create storage of information on how to make a group of proteins for future reference. Source: http://evolution.berkeley.edu/evosite/evo101/IIE2bStudyorigins.shtml

Quick Review of the Steps that Would Give Rise to the First Cell thanks to the Chemistry of early earth 1. Chemicals assembled into Monomers 2. Monomers grouped to form Macromolecules 3. Macromolecules grouped to create early cells (prokaryotes) 4. Macromolecules are able to self replicate which lead to more cells with the same traits 5. Mutations and changes lead to variation 6. Endosymbiosis lead to eukaryotes 7. Colonial eukaryotes lead to multicellular organisms and specialized structures.

The Age of the Earth All of this is difficult to study, because of how long ago it happened. (Earth formed about 4.6 billion years ago [bya] and was too hostile for life for quite some time. The first evidence of life (prokaryotes) in the fossil record appears at 3.5 bya). **The earth is very old!**

The fossil record provides our best timeline for the appearance of organisms on the planet.

Fossil Record Example While every major group (plants, protists, fungi, prokaryotes, and animals) have a pathway of evolution that can be traced through the fossil record, we are going to look at animals as an example. Notice how the order that each major group was found builds on complexity and there is evidence of homology between the groups. Animal Timeline (from earliest to most recent): Animal-Like Protists (ex: amoebas) colonial animal-like protists  Jellyfish/Sponges/Corals  Fish with no bones (sharks)  Fish with bones  Amphibians  Reptiles  Birds and Mammals

Sample Question (AP Test) Fossils of lobe-finned fishes, which are ancestors of amphibians, are found in rocks that are at least 380 million years old. Fossils of the oldest amphibian-like vertebrate animals with true legs and lungs are found in rocks that are approximately 363 million years old. Three samples of rocks are available that might contain fossils of a transitional species between lobe-finned fishes and amphibians: one rock sample that is 350 million years old, one that is 370 million years old, and one that is 390 million years old. (a) Select the most appropriate sample of rocks in which to search for a transitional species between lobe-finned fishes and amphibians. Justify your selection. (b) Describe TWO pieces of evidence provided by fossils of a transitional species that would support a hypothesis that amphibians evolved from lobe-finned fishes.

PRACTICE: Discuss how each of the following influenced the origin of living organisms. a) primordial atmosphere b) photosynthesis c) endosymbiosis theory d) RNA world hypothesis

ANSWERS: Discuss how each of the following influenced the origin of living organisms. a) primordial atmosphere – conditions were right in early earth for organic molecules to form b) photosynthesis – the evolution of photosynthetic prokaryotes added oxygen to the atmosphere and “cleaned up” the hostile atmosphere for life to move onto land c) endosymbiosis theory – eukaryotes evolved from prokaryotes that formed “mega cells” and membrane folding to create organelles d) RNA world hypothesis – self-replicating RNA was the first nucleic acid to form. DNA evolved later as a “gene storage” mechanism from pieces of RNA that combined