Transcript CH1213PartI-Evolution

I. HOW DID LIFE BEGIN?
A. Formation Of The Earth
About billion years ago, the solar
system was a mass of swirling gas
and dust. - Possibly the result of a
supernova.
As millions of years passed, a large amount of material collapsed
to the center and created the sun.
Around 4.6 billion years ago, the earth and
some of the other planets were formed.
As earth cooled, water vapor in the air condensed to form
water and the first oceans. – 3.8-3.9 Billion years ago.
B. Measuring Earth’s Age
-Radiometric dating – estimate of the age of an object by
measuring its content of certain radioactive isotopes.
-Radioactive isotopes – are unstable and “decay” over time.
-The time that it takes for a radioactive isotope to decay by one
half is referred to as its half-life.
C. Life On The Earth
-The oldest evidence of life on the earth can be found in rock that is estimated to
be 3.5 billion years old.
-The evidence shows in the form of fossils.
-The first fossils were referred to as micro-fossils, ancient prokaryotic cells.
1. Formation Of The Basic Chemicals Of Life
A. The “Primordial Soup” Model
-Soviet scientists, alexander oparin (1923),
suggested that the gases of the primitive
atmosphere came together and created simple
organic compounds. (amino acids)
-when the atmosphere cooled and the rain fell, so did the
compounds
-Over time the compounds entered chemical reactions and
proteins and other compounds resulted
*DID NOT run any experiments to support theory
-In 1953, Americans, stanley miller and harold urey, set up an
experiment that was based on Oparin’s theory.
The bubble model
-1986 Louis Lerman suggested that the chemicals needed for life took
place in bubbles on the ocean surface
2. Formation of Complex Organic Compounds
-Formation of protein occurred either by amino acids spontaneously
combining or when they were heated in the absence of oxygen
-Similar mechanisms may have led to the formation of carbohydrates,
lipids, and nucleic acids
3. Concentration and Enclosure
-Experiments have shown that proteins clump together to form
microscopic droplets…
-They include….
A. coacervates - collection of droplets made of molecules of
different types with irregular shape.
B. Microspheres- round, usually from one type of
molecule
-Bear resemblance to living cells but didn’t have the ability
to stay together for extended periods of time.
4. Origins of Heredity
-Not truly understood as to how heredity
originated.
-is agreed that the rna gave rise to dna
II. THE EVOLUTION OF CELLULAR LIFE
A. Evolution of Prokaryotes
Scientists hypothesize:
-That the first cells were prokaryotic because of microfossils found.
- That they were anaerobic and
heterotrophic
because of the lack of oxygen - derived energy through
glycolysis.
-Increased competition made those that could make their own food increase
in number.
B. Evolution of Eukaryotes
-Estimated to of appeared about 1.5 bya
-Not exactly sure how they evolved
-Some early Eukaryotes may have gone through a relationship known as
endosymbiosis.
- theory that prokaryotic intracellular parasites evolved into various cell
organelles – Proposed 1966, lynn Margulis
The theory of endosymbiosis is supported by…
1. size and structure
2. genetic material
3. ribosomes
4. reproduction
III. LIFE INVADES THE LAND
-At about 2.8 billion years ago organisms that went through
photosynthesis gave off oxygen as a waste product.
-Oxygen had two effects on the environment:
1) Those organism that could bond oxygen to other compounds
survived, this was the beginning of aerobic respiration
2) ozone (o3) was created