Earth’s Early History Essential Questions:

How did life on Earth evolve?What were the conditions on Earth like when life evolved?

Early Ideas: Spontaneous GenerationEarly Ideas: Spontaneous Generation• About 2300 years ago, Aristotle argued that air provided a vital life force That could produce life from nonliving substances. This is called spontaneous

generation.

• The idea of spontaneous generation prevailed for thousands of years.

• This idea was not formally tested until the 1700s.

How did we go from

Spontaneous Generation to Biogenesis??Life from air Life from life

• 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.

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.

• Carbon, Hydrogen, Nitrogen, and Oxygen have existed on Earth since its formation.

Early EarthEarly Earth

Early EarthEarly Earth

If early earth was so harsh, how did life come about?!

Key Scientists – Origin of LifeKey Scientists – Origin of LifeFrancesco Redi (1626-1697) • First strike against spontaneous

generation, his work:Remember, around 1678, Anton van Leeuwenhoek observed “animalcules” in water. We now know that these are protozoa.

• Experimental Group: Covered jars with meat = NO maggots

• Control Group: Meat in uncovered jars = maggots

• Conclusion: Only flies where there are maggots AND only maggots where there had been flies… flies must come from flies.

• It was concluded and believed they were a product of spontaneous generation from a “vital force” or life force in the air.

• *As the microscope became a widely used tool for scientists, microorganisms were seen everywhere.

Key Scientists – Origin of LifeLazzaro Spallanzani (1729-1799)

Key Scientists – Origin of LifeKey Scientists – Origin of Life

• Experimental Group: Boiled meat broth and sealed it in flasks = no microorganisms

• Control Group: Boiled meat broth, unsealed flask=microorganisms.

• Conclusion: Only had presence of microorganisms when they had access to the broth.

• *His doubters claimed he had killed the “vital force” in the air when he boiled the broth and it could then not generate life.

It was convincing enough to keep the belief of spontaneous generation going for another 100 years!

Louis Pasteur (1822-1895)

Key Scientists – Origin of LifeKey Scientists – Origin of Life• Experiment: Boiled broth and enclosed it

in an “S” curved neck flask. It was open and exposed to air, however not directly. Exposed for 1 year, no microorganisms; Removed “S” curve and exposed it for 1 day! = microorganisms

• Conclusion: Spontaneous generation was disproved and biogenesis theory was substantiated. (Confirmed, make real or actuated) Contamination came from other microorganisms, not “air”.

• Modern biologists support biogenesis, the idea that “living organisms only come from

other living organisms.”• That then brings up the question of how

life began on Planet Earth.

• If Life can only come from life, we know at some point there had to be a start to “life”… – Where would you start looking for

early life?

Alexander Oparin (1894-1980) NO EXPERIMENTS!!

• Earth’s early atmosphere: HCN, CO2, CO, N, H, S, HOH

• 1936 - Stated that the earliest living organisms on earth were simple heterotrophs (organisms that cannot make their own food)

• Knew these elements (in the form of various gases) were present in the earth’s early atmosphere.

• When heated (geologic activity) they might form organic compounds.

• Once condensed these compounds would be in earth’s water bodies.

• Oparin: “Life arose from the oceans.”• He believed that energy from lightning

and the sun can spark chemical reactions to create macromolecules like proteins.

Heterotrophs ate the organic molecules in their environment

until the food sources were very scarce

Organisms needed another source of energy

Autotrophs evolved (organisms that can make their own food

source)

Oxygen became prevalent in environment so cellular respiration was possible

Eukaryotes evolved

Oparin’s Ideas:

Key Scientists – Origin of LifeKey Scientists – Origin of Life

Alexander Oparin (1894-1980)

Key Scientists – Origin of LifeKey Scientists – Origin of Life

In the 1950’s Stanley Miller and Harold Urey designed an experiment to simulate the conditions of early Earth.

Key Scientists – Origin of LifeKey Scientists – Origin of Life

In the 1950’s Stanley Miller and Harold Urey designed an experiment to simulate the conditions of early Earth.

They used Oparin’s concept and designed a contained

experiment.

They passed sparks (representing lightning)

through a mixture of hydrogen, methane,ammonia, and water

(representing the atmosphere)

Key Scientists – Origin of LifeKey Scientists – Origin of Life

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, a nucleic acid.

Sidney Fox (1912- 1998)• -Studied the development of the first cells; found

structures that have some cell life characteristics.

• Microspheres – microscopic droplet enclosed by a membrane of organic molecules. (Predominantly proteins.)• They can form buds, split and take up certain

substances from surroundings.

• Sydney Fox produced coacervates by heating solutions of amino acids.

• Coacervates – small organic droplet formed by different types of organic molecules. • They can grow and take up substances from

surroundings. (lipid bi-layer)

• NOTE: These are NOT ALIVE no heredity, instead of reproduction, they form spontaneously under proper conditions. Coacervates

Microspheres

Key Scientists – Origin of LifeKey Scientists – Origin of Life

Scientists hypothesize that coacervates acquired more and more characteristics of

living cells as time went on, eventually becoming early forms of bacteria.

Coacervates ProtocellsCoacervates Protocells

ProtocellsProtocells

Protocells are actually theoretical!

They are extremely simplified versions of cells.

They act alive but aren’t!