THERE ARE SEVERAL HYPOTHESES ABOUT THE NATURAL ORIGIN OF L IFE ON EARTH, EACH WITH SUPPORTING

SCIENTIF IC EVIDENCE

EK 1D1

Primitive Earth provided inorganic precursors from which organic molecules could have been synthesized due to the presence of available free energy and the absence of a significant quantity of oxygen

Conditions on Early Earth

Earth was very hot, evaporating the liquid water into the atmosphere

As the earth cooled, gravity-trapped water vapor condensed fell as rain did not boil away but remained impounded in pools that became

lakes and oceansIt was also believed that tectonic activity caused many

volcanic eruptions at that time

From present-day volcanoes, we know that when they erupt Release carbon dioxide Nitrogen And a host of nonoxygen gases

With no protecting atmosphere, the earth was constantly bombarded with Meteorites Other space debris still in circulation from the big bang

From current astronomical research, we know that meteorites can carry Ice and other compounds Including carbon-based compounds

Researchers believe, therefore, that early Earth's atmosphere consisted of water vapor, carbon dioxide, carbon monoxide hydrogen, nitrogen ammonia and methane

How/When Oxygen Appeared

The answer is tiny organisms known as cyanobacteria, or blue-green algaeThese microbes conduct photosynthesis: using sunshine,

water and carbon dioxide to produce carbohydrates and, yes, oxygen

In fact, all the plants on Earth incorporate symbiotic cyanobacteria (known as chloroplasts) to do their photosynthesis for them down to this day

Cells evolved from the functional assembly of organic molecule

Complex molecules may have coalesced inside a space surrounded by a lipid or protein “bubble”

“Bubble” was Precursor of a cell membrane

Here, reactions could proceed more rapidly.

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