 The exact origins of life are unclear  We will examine the most plausible explanations and theories.

 Space programs & imaging  Crust Deposits  Computer Simulations  Fossilized Remains & DNA analysis

 Hubble’s theory of an expanding universe  Redshift and Blueshift  Similar to the doppler effect in sound waves.  15 billion years ago the universe was more concentrated & exploded sending matter and energy into space  Gravity caused the matter to clump together into planets and galaxies.

 Earth’s molten core suggests that Earth began as a hot mass that lost heat from its surface creating the surrounding atmosphere of gases  The atmosphere likely arose from volcanic eruptions and played a role in the origins of living organisms. (still debated )  Geologic evidence does not support the presence of O 2 in the early atmosphere. ◦ But Why?

 Oxygen was trapped in compounds (water & carbon dioxide)  Accumulated after early photosynthetic organisms began to produce it

 Atmosphere was rich in nitrogen and carbon dioxide  Extreme UV radiation from the Sun created a hostile environment on Earth  The now protective Ozone layer did not arise until photosynthetic organisms added O 2 to the atmosphere over millions of years. ◦ Ultraviolent radiation converts O 2 into O 3

 1. Life originated on some planet of another star and traveled to Earth through space on a bicycle. (ET)  2. Life originated by unknown means of Earth  3. Life evolved from nonliving substances through interaction with the environment.

 What makes a hypothesis testable?  Could we design an experiment to test or investigate these 3 explanations?  *Let’s examine some hypotheses and determine their testability*

 Design an experiment to answer a question you have about the natural world ◦ Design needs to include:  The question being investigated  Your hypothesis (“if then statement”)  Procedures (how would you test it)  Variables  Data Collection ( how would you collect data)

 Life evolved from nonliving substances by interacting with the natural environment.  Oparin & Haldane: Energy sources caused atmosphere gases to react and form organic compounds. Accumulation = “Hot Soup”  Chemical Evolution (Fig. 17.8)

 Chemical reactions continued and transformations occurred leading to more organic molecules  Both Oparin and Haldane suggested the first life forms were heterotrophic organisms that survived consuming organic compounds

 3 major steps  There had to be a supply of organic molecules produced by nonbiological processes  Processes had to polymerize molecules into Nucleic Acids & Proteins  Other processes had to organize the polymers into a system that could replicate itself using the organic materials produced in step 1.

 Synthesized organic compounds using electricity & chambered apparatus to recreate Earth’s early atmosphere.  Results: ◦ Small mass of black tar ◦ Water Turned Red (accumulation of unidentifiable compounds) ◦ Combination of gas molecules forming new complex molecules

 The liquid contained amino acids  Amino acids are essential for all living organisms  It was possible cosmic energy reacted with the gases in Earth’s early atmosphere to create organic molecules essential to life

 Examination of meteorite 1969 –found 2 amino acids that do not occur in living organisms on earth.  Halley’s Comet contained several organic compounds including Formaldehyde

 Replication of the system  DNA molecules are the universal information molecule. DNA replication requires proteins. Protein structure is coded in DNA.  SO which came first? Protein or DNA

 The components of RNA can be produced nonbiologically ◦ Ribose, nitrogen, phosphate  The components can join spontaneously  Some RNA molecules can catalyze their own partial replication  This evidence supports the theory that early polymers could organize into systems with the ability to replicate themselves using organic molecules.

 Scientists have not yet found RNA molecules that can replicate themselves completely  Laboratories have been able to simulate Darwinian evolution with RNA molecules that catalyze specific reactions.

 RNA serves as the catalyst in a chemical reaction in some single-celled eukaryotes  RNA molecules that act as enzymes are called Ribozymes  Ribozymes can catalyze changes in other molecules or act on themselves.  Ribozymes that act on themselves are not considered true catalysts because they are changed as a result of the reaction.

 The ability of the RNA molecule to act as a catalyst depends on its three-dimensional structure  A double-stranded region at least 3 base pairs long is needed to stabilize the loops that give the ribozyme its catalytic structure

 According to NASA’s Exobiology Program Life = a self-sustained chemical system that is capable of undergoing Darwinian, or biological, evolution

 Biological Evolution consists of 3 processes ◦ Self-reproduction ◦ Mutation that can be inherited ◦ Natural Selection  Example organism that undergo these processes include ◦ Humans, bacteria, lizards ◦ Basically all living organisms on the Earth

 The oldest know microfossils are of tiny, single-celled filaments ◦ Found in northwestern Australia  The discovery of these microfossils provide evidence that life appeared on Earth much early than previously thought. ◦ Found in rocks formed almost 3.5 billion years ago 

 Carl Woese suggests that the first microorganisms were methanogens which are anaerobic bacteria that obtain energy by using carbon dioxide to oxidize hydrogen.  Methanogens live in extreme conditions thought to be like those of the early earth (extremophiles)  They can live near hydrothermal volcanic vents(hot) or rock wastes from mining (acidic)

 The first microfossils determined to be eukaryotic are around 2.1 billion years old.  Fossil evidence indicates eukaryotes thrived around750 million years ago  Endosymbiotic theory: eukaryotes evolved from the symbiotic relationships among various prokaryotic organisms  Lynn Margulis hypothesized that mitochondria and plastids originated as free-living prokaryotes

 Symbiotic relationships among the prokaryotes may have provided those organisms with an environmental advantage compared to the prokaryotes lacking the symbiotic abilities.  Internal partners are called endosymbionts.

 LO 1.27 Student is able to describe a scientific hypothesis about the origin of life on Earth  LO 1.28 Student is able to evaluate scientific questions based on the hypotheses about the origin of life on Earth  LO 1.29 Student is able to describe reasons for revisions of scientific hypotheses of the origin of life on Earth  LO 1.32 Student is able to justify the selection of geological, physical, and chemical data that reveal early Earth conditions.