Life on EarthLife on Earth

Early Earth What was Early Earth like? Scientific Theories about evolution of organic

molecules Chemicals before cells Pasteur/Virchow, Oparin, Urey/Miller Biochemical studies Search for evidence

Early EarthEarly Earth

Origins of Universe - 10-20 billion yrs old- Big Bang- Expanding ever since- Some parts condensed to form Solar Systems or

groups of solar systems called Galaxies- Earth about 4.5 billion yrs old: most /all of the

elements we know today had formed

What was Early Earth like?What was Early Earth like? Clouds of water vapour originally surrounding

Earth,condensed to form oceans and seas, still HOT! One/two large land masses – Pangaea Volcanoes spewed ash and lava Atmosphere: gases Hydrogen, carbon monoxide, carbon

dioxide (lots), methane, ammonia, nitrogen BUT NO OXYGEN

Electrical storms and cosmic rays produced explosive energy able to penetrate THIN atmosphere

CARBON (organic) compounds managed to originate in this hostile environment, 4 billion yrs ago

Once biological chemicals were present, primitive cells emerged about 3.5 billion yrs ago.

Scientific Theories about the Scientific Theories about the evolution of organic moleculesevolution of organic moleculesSPONTANEOUS GENERATION: people

thought life arose from non-living matter.They ‘saw’ maggots appear in rotting meat,

frogs arise from moist earth and fish from muddy water.

Not scientifically tested until 1668 – Redi demonstrated that the maggots in decaying meat came from eggs laid by flies fig 3.2.1

100yrs later- Spallanzani : microorganisms that appeared in broth came from air (but this could not EXCLUDE spontaneous generation) fig 3.2.2

100 yrs later 1862- Louis Pasteur convinced people that Spontaneous Generation did NOT occur fig 3.2.3

Chemicals before CellsChemicals before Cells

Pasteur / Virchow and others stated that “All life comes from pre-existing life”1923 Oparin: ‘before living things could

arise, living chemicals must be formed”He believed gases in primitive atmosphere

could be converted ito molecules of biological chemicals

NOT tested until 1950’s by Urey+ Miller

Urey – Miller Urey – Miller ExperimentExperiment Simulated conditions of early earth and to test for biological chemicals Fig 3.2.4 Set up apparatus containing gases- hydrogen, methane,

ammonia and water vapour. Gases were circulated between lower chamber of water

(‘oceans’) and upper chamber (‘atmosphere’) Electrical discharge passed through atmosphere chamber

to simulate energy in early atmosphere Samples withdrawn from fluid and atmosphere chambers

contained amino acids and other organic molecules!!

Further experiments: used UV light instead of electricity and this produced nitrogenous bases, ribose, nucleotides and amino acids.

It did NOT prove conclusively however, the origin of life but DID prove it was possible for non-living matter to produce living matter and this Chemosynthetic Origin of Life is believed by most biologists today.

Chemicals from Outer SpaceChemicals from Outer Space

NO concrete evidence that chemicals came from outer space

However, carbon has been detected on other planets, meteorites and comets and floating freely in giant space clouds.

Meteorites found on Earth contain organic chemicals such as Amino acids and what appears to be fossils.

Significance of Significance of Chemosynthetic and Outer Chemosynthetic and Outer

Space theoriesSpace theoriesUniverse began protons, neutrons + electrons + hydrogen

present specific conditions (heat and pressure) other elements formed simple compounds form

Biochemical StudiesBiochemical Studies

All living organisms contain same type of basic chemicals eg Amino acids and sugars

Most elements and many simple compounds: hydrogen sulfide, ammonia, methane, water – existed for 6 billion yrs at least but NO biological chemicals

Nonliving (early compounds) before biological compounds (chemosynthetic theory) or came from Outer space as ready made cells???

Search for EvidenceSearch for Evidence

Most experiments try to replicate evolution of chemicals (Urey-Miller)

Search Outer space for more living matter All scientists agree that for living matter to evolve,

the chemicals of life must be present first for them to then become organised into cells.

Evolution from a cellular state to present day life forms took long periods of time therefore chemicals must have evolved before first cells appeared