Transcript National Academy of Sciences

The National Academy of Sciences
In everyday usage: "theory" often refers to a
hunch or a speculation. The word, “theory” is
often used when drawing a conclusion based
on inconclusive evidence.
The formal scientific definition of theory: It refers
to a comprehensive explanation of some aspect
of nature that is supported by a vast body of
evidence.
National Academy of Sciences
“Scientific theories are so well-established that no new evidence is
likely to alter them substantially.”
• Example: No New Evidence will Demonstrate:
–
–
–
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that the Earth does not orbit around the sun (heliocentric theory)
that living things are not made of cells (cell theory)
that matter is not composed of atoms (atomic theory)
that the surface of the Earth is not divided into solid plates that have
moved over geological timescales (the theory of plate tectonics)
• How does this relate to the theory of evolution?
– It is supported by so many observations and confirming
experiments that the basic components of the theory will not
be overturned by new evidence.
– However, like all scientific theories, the theory of evolution is
subject to continuing refinement as new areas of science
emerge or as new technologies enable observations and
experiments that were not possible previously.
In the past, people believed in spontaneous generation-the idea that nonliving material can produce life out of
no-where. (if you had corn, mice would appear)
After all, maggots magically appeared on meat as if out
of nowhere.
This idea was disproved by the microscope.
Micro-organisms are all over the place.
But if living things only come from other living things, then
where did the first living thing come from?
Francesco Redi
This is a question that scientists have hypothesized and
theorized over:
What is the scientific explanation of how life first
appeared on our planet?????
Scientists hypothesize that on primitive Earth it was
very hot, where lava and toxic gases were constantly
spewed from volcanic eruptions- not conditions
conducive to life as we know it.
We have no record of life’s origin, probably because movements
in the mantle and crust, volcanic activity, and erosion obliterated
all traces of it.
The oldest fossils of living things that have been found resemble
anaerobic prokaryotes
(single-celled bacterium that did not require oxygen)
We can however put together possible scientific explanations of
how life originated by considering three questions:
-Can we identify physical and chemical conditions that prevailed on the Earth when life
originated?......HOW COULD WE DO THIS?
-Do the known principles of physics, chemistry, and evolution support or disprove the
hypothesis that large organic molecules (Bio-molecules) formed spontaneously and
evolved into the fundemental properties of life?
-Can we design experiments to test the hypothesis that living systems emerged through
chemical evolution?
By studying primitive rock and young planets
much like ours, scientists theorize that…..
Earth’s early atmosphere consisted of:
- water vapor (steam)
- hydrogen
- ammonia ( NH³)
- methane (CH4 )
There was no free oxygen ( O ) on our planet.
2
Living organisms are made of four main bio-molecules.
Carbohydrates
Proteins
Nucleic Acids
Lipids
Many scientists have hypothesized and theorized how
the gases on primitive Earth could have joined together
to form bio-molecules so that life could occur.
Russian scientist (1930s), Alexander Oparin
hypothesized that life began in the oceans.
He believed that energy from the sun, heat, and
lightning from constant storms triggered chemical
reactions that caused different molecules on Earth to
join together to form bio-molecules.
AfterIn
their
1953,
experiment,
two American
they scientists
discovered
Miller
that and
amino
Urey
acids,
sugars,
actually
lipids,
tested
and Oparin’s
other organic
hypothesis
molecules
by simulating
had formed
in the
conditions
“oceanicofcompartment!”
early Earth.
These molecules were formed from ABIOTIC factors.
They added
electricity to
simulate the
lightning
present.
They added
water vapor.
They added the
atmospheric
gases that
were said to be
present at the
time.
From there, various other experiments were created and
carried out to take the data further- can these subunits
bond together to form acutal bio-molecules?…..after
amino acids were heated without oxygen, they began to
link and form proteins. (NA as well)
In 1992 a biochemist named Sidney Fox produced very
simple cell-like structures called protocells by heating
the proteins and other bio-molecules together.
Amino acids
join to form
proteins
Before there were oceans
When oceans were forming
Early oceans and atmosphere
Our oceans today
Science tells us the
Earth is very old.
4.6 billion years give
or take!
Geologists have
organized Earth’s
history into
different periods.
The largest intervals of
geologic time are called EONS
and are hundreds of MILLIONS
of years long.
EONS
Eons are broken down into
ERAS
Phanerozoic Eon
(the present eon)
is divided into three
eras: Paleozoic,
Mesozoic, and the
present Cenozoic.
ERAS
PERIODS
Eras are lastly broken down into
PERIODS
TERTIARY
We are currently in the
Quarternary period of the
Cenozoic Era.
Lets start at the beginning and make our
way to NOW.
The Precambrian Eon
● Makes up 87% of Earth’s history thus far
● It includes the hypothesized beginning of Earth
4,600,000,000 Billion years ago up to
544,000,000 Million years ago
(so it was approx. four billion years long)
It includes when prokaryotes formed….then eukaryotes….plants, then to simple
invertebrates near the end of this eon (according to fossil records)
The Phanerozoic Eon
● Goes from 544,000,000 Million years ago to the
present.
● This Eon includes: multi-cellular animal species explosions
several mass extinctions
dinosaurs
humans
Ice Ages