2. Four processes were needed for the spontaneous origin of life on early Earth:
Non-living synthesis of simple organic molecules

3. All of the elements found in organic compounds are thought to have existed on Earth and in the rest of the solar system when the Earth formed.
But how and where were these elements assembled into the organic compounds found in life? 

4. What was early Earth like? (Through the Wormhole video clip #1)

5. About 4.6 billion years ago the planets of our solar system formed by the condensing of matter around our sun
Our solar system was filled with hot gases and dust, which swirled and revolved around a white hot core. When the core approached one million degrees Fahrenheit, our sun was born. The gaseous dust clouds gradually condensed and formed asteroids. It is estimated that over 100 trillion planetesimals, or large asteroids, existed when our solar system was formed. As these huge pieces of matter were revolving around the sun, many of them collided with one another. While some of these collisions destroyed the planetesimals, others caused them to combine. As their mass increased, gravity pulled in more particles and debris, and the planetesimals grew larger. This process, called accretion, is how the earth and the other planets were formed.

6. The Surface Bombardment by meteorites.
Water vapor condensed to liquid, forming oceans.
As the planet earth continued to be hit by meteorites, cosmic H2O was released from the meteorites and from the crust of the earth. This gaseous H2O rose into the atmosphere, combined with CO2 and other gases, and formed incredibly dense clouds above the earth. These clouds formed a reflective shield above the earth, keeping solar heat from penetrating to the surface. As the frequency of meteorite impacts declined, the surface of the earth began to cool. When this happened, the immense clouds which had emerged began to pour rain over the entire planet, cooling the molten rock, and creating lakes and oceans.

7. There were frequent lightning / electrical storms

8. The Temperatures were high
(little atmosphere to shield heat from the sun)

9. Earth’s primitive atmosphere formed by volcanic out gassing.
The Atmosphere
Earth’s primitive atmosphere formed by volcanic out gassing.
Radioactive decay caused Earth’s core to heat and gases to build up in the Earth's core. This caused huge volcanoes to spew forth molten rock, or lava, as well as various gases which had been trapped under the surface of the Earth.

10. The Atmosphere: Then vs Now
UV light penetrated Earth’s atmosphere
NOW:
UV is absorbed by ozone in the atmosphere

11. The Atmosphere: Then vs. Now
Uncertainty remains
THEN (?):
Consisted of:
Methane
Ammonia
Water vapor
Nitrogen gas
Carbon dioxide
Hydrogen gas
Carbon monoxide
NOW:
Consists of:
Nitrogen gas (N2)
Oxygen gas (O2)
Based on today's volcanic evidence, this atmosphere would have contained 80% water vapor, 10% carbon dioxide, 5 to 7% hydrogen sulfide, and smaller amounts of nitrogen, carbon monoxide, hydrogen, methane and inert gases

12. The Atmosphere: Then vs. Now
Reducing
atmosphere:
lack of O2 allows formation of complex organic molecules
NOW:
Oxidizing
atmosphere:
free O2 inhibits formation of complex organic molecules
Oparin’s Hypothesis (1923)

13. Uncertainty
Growing evidence suggests that the early atmosphere was made up primarily of nitrogen and carbon dioxide and was neither reducing nor oxidizing.

14. Two testable hypothesized mechanisms for the presence of simple organic molecules on Earth:
Organic molecules were created from inorganic matter on Earth
Organic molecules were delivered to Earth from outer space

15. Miller and Urey (1953) duplicated Oparin’s early Earth conditions in the lab

16. Methods:
In a glass refluxing system, they recreated a miniature ocean-atmosphere system

17. They included hydrogen, methane, ammonia and water into the system to model Oparin’s hypothesized pre-biotic atmosphere.
The gases they used were methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). He ran a continuous electric current through the system, to simulate lightning storms believed to be common on the early earth.

18. The mixture was heated and circulated past an electric spark (to model lightening) before allowing it to condense

19. Amino acids were formed from the inorganic compounds
Analysis of the experiment was done by chromatography. At the end of one week, Miller observed that as much as 10-15% of the carbon was now in the form of organic compounds. Two percent of the carbon had formed some of the amino acids which are used to make proteins.
ANIMATION

20. Other scientists repeated Miller and Urey’s work, eventually producing:
Other amino acids
ATP
Glucose and other sugars
Lipids
Bases which form RNA and DNA
Adenine (the key component of ATP)
These molecules would accumulate over long time periods producing thick, warm "primordial soup“
In 1961, Juan Oro found that amino acids could be made from hydrogen cyanide (HCN) and ammonia in an aqueous solution. He also found that his experiment produced an amazing amount of the nucleotide base, adenine. Adenine is of tremendous biological significance as an organic compound because it is one of the four bases in RNA and DNA. It is also a component of adenosine triphosphate, or ATP, which is a major energy releasing molecule in cells. Experiments conducted later showed that the other RNA and DNA bases could be obtained through simulated prebiotic chemistry with a reducing atmosphere.

21. Conclusion: molecules of life can arise from non-living material TOK: we may be able to show that organic compounds could arise under certain conditions, but we can't determine with certainty whether they did in the past
Perhaps most importantly, Miller's experiment showed that organic compounds such as amino acids, which are essential to cellular life, could be made easily under the conditions that scientists believed to be present on the early earth. This enormous finding inspired a multitude of further experiments.
There has been a recent wave of skepticism concerning Miller's experiment because it is now believed that the early earth's atmosphere did not contain predominantly reductant molecules. Another objection is that this experiment required a tremendous amount of energy. While it is believed lightning storms were extremely common on the primitive Earth, they were not continuous as the Miller/Urey experiment portrayed. Thus it has been argued that while amino acids and other organic compounds may have been formed, they would not have been formed in the amounts which this experiment produced.
Instead of forming in the atmosphere, the first organic compounds on Earth may have been synthesized near submerged volcanoes and deep–sea vents—weak points in Earth’s crust where hot water and minerals gush into the ocean.

22. Two testable hypothesized mechanisms for the presence of simple organic molecules on Earth:
Organic molecules were created from inorganic matter on Earth
Organic molecules were delivered to Earth from outer space

23. Extraterrestrial Hypothesis
Comets contain a variety of organic compounds.
Heavy bombardment 4,000 million years ago may have delivered both organic compounds and water to the early Earth.
Analysis of light spectra of comets

24. Example: Murchison Meteorite Rich with amino acids
Demonstrates that Earth may have acquired organic compounds from space
Many of the compounds made in the Miller/Urey experiment are known to exist in outer space. On September 28, 1969, a meteorite fell over Murchison, Australia. While only 100 kilograms were recovered, analysis of the meteorite has shown that it is rich with amino acids. Over 90 amino acids have been identified by researchers to date. Nineteen of these amino acids are found on Earth. (table showing comparison of Murchison meteorite to Miller/Urey experiment) The early Earth is believed to be similar to many of the asteroids and comets still roaming the galaxy. If amino acids are able to survive in outer space under extreme conditions, then this might suggest that amino acids were present when the Earth was formed. More importantly, the Murchison meteorite has demonstrated that the Earth may have acquired some of its amino acids and other organic compounds by planetary infall.

25. A wilder offshoot of this theory, suggests that whole bacteria—life itself—first evolved on Mars and then hitched a ride to Earth via small pieces of the Red Planet blasted here by asteroid or comet impacts. But no life has been found on Mars, and the one claim of fossil bacteria in a Martian meteorite, made by NASA scientists in 1996, has been almost universally rejected.

26. Four processes were needed for the spontaneous origin of life on Earth:
Non-living synthesis of simple organic molecules
Assembly of these molecules into polymers

28. Assembly of these molecules into polymers 4 hypothesized locations:
Ocean-land interface hypothesis
Under hypothesis
Clay hypothesis
Hydrothermal vent hypothesis

29. Ocean-Land Interface Hypothesis
Early oceans carried simple organic molecules
The porous surfaces of shoreline minerals helped organize such building blocks into polymers.
Perhaps the leading theory focuses on the slimy interface where the sea laps against land. If early oceans carried organic molecules—and they most likely did—the porous surfaces of shoreline minerals could have helped organize such building blocks into primitive structures.

30. Under Ice Hypothesis
Some scientists calculate that at one point, the top 300 meters of the ocean were frozen over.
According to some solar evolution models, the sun was some 30 percent dimmer at that time, providing less heat to Earth. So as soon as the hail of asteroids stopped, Earth may have cooled to an average surface temperature of –40°F and a crust of ice as much as 1,000 feet thick may have covered the oceans.
You might think that icy cold water trapped under hundreds of meters of ice would not be beneficial to life beginning, but in fact it is advantageous in many aspects. One advantage is that the layer of ice would provide a protective shield by preventing ultra-violet light, which enters the earth's atmosphere and destroys organic compounds, from reaching the developing molecules. Another advantage is that it would provide safety from the devestating effects of impact frustration. ( Definition Box -Impact frustration is a theory which says that life may potentially have arisen many times, but was wiped out due to severe bolide impacts) The water beneath the ice would be cold, allowing for organic molecules to survive over much longer periods of time. These organic molecules could have been provided by the hydrothermal vents still prevalent on the ocean floor today. With a sufficient supply of organic molecules safe from ultra-violet radiation and bolide impact frustration, many believe that this was the environment allowing life to get a foothold on a hostile earth.
With a barrier between the atmosphere and the ocean, the debate concerning the composition of the atmosphere becomes much less significant. All of the components needed for organic syntheses such as the Strecker synthesis would be provided and kept stable, while the bottom of the ocean would provide a place for organics to gather and react. Following this reasoning, the atmospheric composition may only be important after life came out of the water, when life had already begun.

31. Ice provided a protective shield from UV light (which destroys organic compounds)
Organic compounds are more stable in colder temperatures and could combine in a lattice of ice.
You might think that icy cold water trapped under hundreds of meters of ice would not be beneficial to life beginning, but in fact it is advantageous in many aspects. One advantage is that the layer of ice would provide a protective shield by preventing ultra-violet light, which enters the earth's atmosphere and destroys organic compounds, from reaching the developing molecules. Another advantage is that it would provide safety from the devestating effects of impact frustration. ( Definition Box -Impact frustration is a theory which says that life may potentially have arisen many times, but was wiped out due to severe bolide impacts) The water beneath the ice would be cold, allowing for organic molecules to survive over much longer periods of time. These organic molecules could have been provided by the hydrothermal vents still prevalent on the ocean floor today. With a sufficient supply of organic molecules safe from ultra-violet radiation and bolide impact frustration, many believe that this was the environment allowing life to get a foothold on a hostile earth.
With a barrier between the atmosphere and the ocean, the debate concerning the composition of the atmosphere becomes much less significant. All of the components needed for organic syntheses such as the Strecker synthesis would be provided and kept stable, while the bottom of the ocean would provide a place for organics to gather and react. Following this reasoning, the atmospheric composition may only be important after life came out of the water, when life had already begun.
Proposed by Miller’s graduate student. He was looking at samples from the Miller experiment that had been frozen for 25 years and he actually saw the percentage of some compounds had increased in the sample.
The skepticism they faced was understandable. Chemical reactions do slow down as the temperature drops, and according to standard calculations, the reactions that assemble cyanide molecules into amino acids and nucleobases should run a hundred thousand times more slowly at –112°F than at room temperature. This is the main argument against Miller’s experiment, and against a cold origin of life in general. But strange things happen when you freeze chemicals in ice. Some reactions slow down, but others actually speed up—especially reactions that involve joining small molecules into larger ones. This seeming paradox is caused by a process called eutectic freezing. As an ice crystal forms, it stays pure: Only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Chemically speaking, it transforms a tepid seventh-grade school dance into a raging molecular mosh pit.

32. Hydrothermal Vent Hypothesis
Release hot gaseous substances which may fuel polymerization
Today, they are surrounded by thriving ecosystems
One current theory is that life originated deep beneath the surface of the ocean at deep sea hydrothermal vents. These hydrothermal vents were first discovered in Soon after, scientists made an exciting discovery. These vents release hot gaseous substances from the center of the earth at temperatures in excess of 700oF. Previously scientists were sure that life could not exist, deep beneath the surface of the ocean. After the discovery of hydrothermal vents, they found ecosystems thriving in the depths of the ocean. These ecosystems contained various types of fish, worms, crabs, bacteria and other organisms which had found a way to survive in a cold, hostile environment without energy input from sunlight. Because life had been found to exist where it previously was thought unable to, many scientists began to ask questions as to whether or not this was where life may have originated on the earth.
VIDEO

34. Hydrothermal Vent Hypothesis
On the molecular level, the chances of life originating at deep sea thermal vents is not likely. It is known that organic molecules are unstable at high temperatures, and are destroyed as quickly as they are produced. It has been estimated that life could not have arisen in the ocean unless the temperature was less than 25oC, or 77oF.
Supporters of this theory claim that the organic molecules at the thermal vents are not formed in 300oC temperatures, but rather in a gradient formed between the hydrothermal vent water, and the extremely cold water, 4oC (39.2oF), which surrounds the vent at the bottom of the ocean. The temperatures at this gradient would be suitable for organic chemistry to occur. Debates still remain, however, as to the gradient's effectiveness in producing organic compounds.

35. Clay Hypothesis
Clay contains iron and zinc atoms which can serve as inorganic catalysts for polypeptide formation
Clay collects energy from radioactive decay and discharges it if temperature or humidity changes; could have been source of energy for polymerization to take place
VIDEO

36. Four processes were needed for the spontaneous origin of life on Earth:
Non-living synthesis of simple organic molecules
Assembly of these molecules into polymers
Origin of self replicating molecules that made inheritance possible
Packaging of these molecules into membranes with an internal chemistry different from their surroundings

37. In modern living systems, information flows from

38. WHAT IS RNA?

39. Each consists of a base, a ribose sugar, and a phosphate group.
One of the four major biomolecules (along with lipids, carbohydrates and proteins)
What is RNA?
Ribonucleic acid is a nucleic acid
RNA is essential for all known forms of life.
Like DNA, RNA is made up of a long chain of nucleotides.
Each consists of a base, a ribose sugar, and a phosphate group.

40. How is RNA different than DNA?
RNA contains the sugar ribose, while DNA contains the slightly different sugar deoxyribose
RNA has the base uracil while DNA contains thymine.
Unlike DNA, most RNA molecules are single-stranded and can adopt very complex three-dimensional structures.

42. REMEMBER: In modern living systems, information flows from

43. DNA  RNA  Protein This sequence probably developed in stages

44. RNA-First Hypothesis Through the Wormhole video clip #2
The first genetic information and enzymes were RNA molecules
Why RNA? RNA can act as a catalyst to:
Bind amino acids together to form proteins
Replicate itself to create more RNA (animation #1)

45. RNA can be transcribed to DNA
This could have given rise to the first DNA

47. DNA is more stable than RNA and eventually took over carrying the genetic information

48. Arguments for the RNA First hypothesis
In Miller’s experiments, ribose was created and deoxyribose was harder to produce.
RNA has a simpler structure then DNA.
RNA exists in viruses (and no DNA)
It has been proved experimentally that RNA has catalytic functions (it is a catalyst)
The DNA-protein system cannot work without RNA.

49. Four processes were needed for the spontaneous origin of life on Earth:
Non-living synthesis of simple organic molecules
Assembly of these molecules into polymers
Origin of self replicating molecules that made inheritance possible
Packaging of these molecules into membranes with an internal chemistry different from their surroundings

50. Protocells: Combinations of abiotically produced molecules surrounded by a membrane or membrane–like structure.

51. Exhibit some of the properties associated with life
simple reproduction
simple metabolism
the maintenance of an internal chemical environment different from that of their surroundings.

52. Protocells could have developed from coacervate droplets:
Complex spherical units that spontaneously form when concentrated mixtures of macromolecules are held in the right temperature, ionic composition, and pH
Absorb and incorporate various substances from the surrounding solution
Laboratory experiments demonstrate that protocells could have formed spontaneously from abiotically produced organic compounds. For example, small membrane–bounded droplets called liposomes can form when lipids or other organic molecules are added to water.

53. How could a protocell develop?
Fatty acids spontaneously form membranes (animation #4, video clip #3 from Wormhole)
RNA enters the membrane (animation #5)
Creates proteins
Replicates itself
Structure divides into two when surface area is too large (animation)