Capitulo 1: El Origen de la Vida

Capitulo 1: El Origen de la Vida
• En una clase de la Historia de la Vida
comenzamos discutiendo su origen.
• Sabemos que existe vida en nuestro planeta
pero no sabemos donde y como se origino.
• No tenemos evidencia de vida en ninguna
otra parte de nuestro universo.
• Debemos suponer que la vida, como la
conocemos, se origino en este planeta.
1: El orgánicas
Origen complejas
de la Vida
• Capitulo
Existen moléculas
en
el espacio, cometas, meteoritos etc..
• Estas son el resultado de gas interestelar
expuesto a radiación cósmica y estelar.
• Estas probablemente se estrellaban contra el
planeta Tierra en ocasiones, siendo así una
fuente de moléculas orgánicas.
• Sin embargo este proceso no resultara en el
desarrollo de la vida. Además en nuestro
planeta también se pueden formar
moléculas orgánicas.
• Para determinar como comenzó la vida en
nuestro planeta podemos reconstruir como
se formo nuestro sistema solar y nuestro
planeta.
• Con la ayuda de los biólogos podemos
entonces tratar de reconstruir el origen de la
vida.
• La vida como la conocemos esta compuesta
mayormente por agua en su estado liquido.
• No podemos imaginarnos que exista vida
sin agua, por lo cual necesitamos planetas
con agua (océanos) para crear vida.
Origen de Nuestro Sistema Solar
• Los astrónomos creen que el universo tiene
15 billones de años de antigüedad. Los
primeros elementos comenzaron a formarse
(hidrógeno y helio).
• Fuerzas gravitacionales colapsaron nubes de
estas partículas para formar estrellas.
• El 99% de las partículas se unieron para
formar estrellas (el sol).
• Un 1% de este polvo estelar quedo en orbita
alrededor del sol.
Los planetas
• Partículas de polvo tienden a unirse por
fuerzas electroestáticas en un proceso
conocido como “acreción”:
– Ej. Mota de polvo debajo de sus camas.
• Planetas pequeños se pueden haber formado
de la misma manera cuando las partículas
de polvo, en orbita alrededor del sol, se
unieron.
Nuestro sistema solar esta compuesto por:
Mercurio
Venus
Tierra
Marte
Júpiter
Saturno
Urano
Neptuno
Plutón
De estos solo los primeros 4
Planetas tienen la posibilidad
de tener agua en su estado
Liquido.
• Cada uno de estos cuatro planetas comenzó
como una masa de material derretido como
resultado de los choques entre planetas mas
péguenos que los formaron.
• Eventualmente su capa exterior se enfrío y
formo una corteza.
• Una ves se enfrío la superficie de los
planeta, la temperatura exterior del planeta
depende por completo de la distancia del sol
y de los gases volcánicos que salen a la
superficie durante las erupciones.
Tamaño y distancia del Sol.
• A mayor distancia del Sol menos efectos de
los rayos solares (mas frió).
• El tamaño determina si hay actividad
volcánica. Esta actividad volcánica resulta
en gases atmosféricos que producen una
atmósfera y el efecto de casa de
invernadero.
• Un planeta pequeño no puede retener los
gases en su atmósfera debido a un campo
gravitacional débil.
Mercury
Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it
has no plate tectonics.
Mercury actually has a very thin
atmosphere consisting of atoms blasted
off its surface by the solar wind.
Because Mercury is so hot, these atoms
quickly escape into space. Thus in
contrast to the Earth and Venus whose
atmospheres are stable, Mercury's
atmosphere is constantly being
replenished.
Venus
Venus
Venus, the jewel of the sky, was once know by ancient astronomers as the
morning star and evening star. Early astronomers once thought Venus to be
two separate bodies. Venus, which is named after the Roman goddess of love
and beauty, is veiled by thick swirling cloud cover.
Astronomers refer to Venus as Earth's sister planet. Both are similar in size,
mass, density and volume. Both formed about the same time and condensed out
of the same nebula. However, during the last few years scientists have found
that the kinship ends here. Venus is very different from the Earth. It has no
oceans and is surrounded by a heavy atmosphere composed mainly of carbon
dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid
droplets. At the surface, the atmospheric pressure is 92 times that of the Earth's
at sea-level.
Venus is scorched with a surface temperature of about 482° C (900° F). This
high temperature is primarily due to a runaway greenhouse effect caused by the
heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to
heat the surface of the planet. Heat is radiated out, but is trapped by the dense
atmosphere and not allowed to escape into space. This makes Venus hotter than
Mercury.
A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly,
Venus rotates from east to west. To an observer on Venus, the Sun would rise in
the west and set in the east.
La Luna
No hay agua, no hay
evidencia de agua en
estado liquido en el
pasado y no hay vida.
Mars
Mars is the fourth planet from the Sun and is commonly referred to
as the Red Planet. The rocks, soil and sky have a red or pink hue. The
distinct red color was observed by stargazers throughout history. It
was given its name by the Romans in honor of their god of war.
Other civilizations have had similar names. The ancient Egyptians
named the planet Her Descher meaning the red one.
Before space exploration, Mars was considered the best candidate for
harboring extraterrestrial life. Astronomers thought they saw
straight lines crisscrossing its surface. This led to the popular belief
that irrigation canals on the planet had been constructed by
intelligent beings. In 1938, when Orson Welles broadcasted a radio
drama based on the science fiction classic War of the Worlds by H.G.
Wells, enough people believed in the tale of invading Martians to
cause a near panic.
Another reason for scientists to expect life on Mars had to do with
the apparent seasonal color changes on the planet's surface. This
phenomenon led to speculation that conditions might support a
bloom of Martian vegetation during the warmer months and cause
plant life to become dormant during colder periods.
Ophir Chasma is a large west-northwesttrending trough about 100 km wide. The
Chasma is bordered by 4 km high walled
cliffs, most likely faults, that show spurand-gully morphology and smooth
sections. The walls have been dissected
by landslides forming reentrants; one area
(upper left) on the north wall shows a
young landslide about 100 km wide. The
volume of the landslide debris is more
than 1000 times greater than that from the
May 18, 1980 debris avalanche from
Mount St. Helens. The longitudinal
grooves seen in the foreground are
thought to be due to differential shear and
lateral spreading at high velocities. The
landslide passes between mounds of
interior layered deposits on the floor of
the chasma. (Courtesy USGS)
No hay agua en estado liquido
In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealed
was a surface containing many craters and naturally occurring channels but no evidence of
artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2
touched down on the surface of Mars. The three biology experiments aboard the landers
discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no
clear evidence for the presence of living microorganisms in the soil near the landing sites.
According to mission biologists, Mars is self-sterilizing. They believe the combination of solar
ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the
oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian
soil. The question of life on Mars at some time in the distant past remains open.
Other instruments found no sign of organic chemistry at either landing site, but they did
provide a precise and definitive analysis of the composition of the Martian atmosphere and
found previously undetected trace elements.
Evidencia de canales naturales.
Atmosphere
The atmosphere of Mars is quite different from that of Earth. It is composed primarily of
carbon dioxide with small amounts of other gases. The six most common components of the
atmosphere are:
*
*
*
*
*
*
Carbon Dioxide (CO2): 95.32%
Nitrogen (N2): 2.7%
Argon (Ar): 1.6%
Oxygen (O2): 0.13%
Water (H2O): 0.03%
Neon (Ne): 0.00025 %
Martian air contains only about 1/1,000 as much water as our air, but even this small amount
can condense out, forming clouds that ride high in the atmosphere or swirl around the slopes
of towering volcanoes. Local patches of early morning fog can form in valleys. At the Viking
Lander 2 site, a thin layer of water frost covered the ground each winter.
There is evidence that in the past a denser martian atmosphere may have allowed water
to flow on the planet. Physical features closely resembling shorelines, gorges, riverbeds
and islands suggest that great rivers once marked the planet.
Temperature and Pressure
The average recorded temperature on Mars is -63° C (-81° F) with a maximum temperature of
20° C (68° F) and a minimum of -140° C (-220° F).
Earth
EARTH
Earth is the 3rd planet from the Sun at a distance of about 150 million kilometers (93.2 million
miles). It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for the
Earth rotate a complete revolution. It has a diameter of 12,756 kilometers (7,973 miles), only a
few hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percent
nitrogen, 21 percent oxygen and 1 percent other constituents.
Earth is the only planet in the solar system known to harbor life. Our planet's rapid spin
and molten nickel-iron core give rise to an extensive magnetic field, which, along with the
atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and
other stars. Earth's atmosphere protects us from meteors, most of which burn up before
they can strike the surface.
From our journeys into space, we have learned much about our home planet. The first
American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen
radiation belts. This layer is formed from rapidly moving charged particles that are trapped by
the Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findings
from satellites show that our planet's magnetic field is distorted into a tear-drop shape by the
solar wind. We also now know that our wispy upper atmosphere, once believed calm and
uneventful, seethes with activity -- swelling by day and contracting by night. Affected by
changes in solar activity, the upper atmosphere contributes to weather and climate on Earth
• El planeta Tierra tiene el tamaño adecuado; no se
ha enfriado en su interior lo que resulta en
actividad volcánica que lleva gases a la atmósfera
continuamente.
– Erupción volcánica en Kilauea, 50% vapor de agua
• También tiene, como resultado de su tamaño, una
atmósfera que atrapa los gases (continuamente los
gases escapan de nuestra atmósfera).
• El planeta tierra se encuentra a una distancia
adecuada del sol para que el agua se encuentre en
sus estados sólido, liquido y gaseoso.
Reconstruyendo el origen de la
Vida
En nuestro planeta, una atmósfera primitiva
bañada de luz ultravioleta del sol, resultaría
en gases que se disolverían fácilmente en
agua enriqueciendo el océano con carbón.
Estos gases serian amonia (NH3), metano
(CH4), y monóxido de carbono (CO).
Reconstruyendo el origen de la
Vida
• Uno de los productos químicos de la
combinación de estos productos seria
cianuro (HCN).
• Este es uno de los bloques básicos en la
construcción de moléculas orgánicas mas
complejas.
Stanley Miller
• Miller, en la Universidad de Chicago
decidió reconstruir como seria una
atmósfera primitiva para ver que reacciones
químicas ocurren y sus resultados.
Miller, en un espacio sellado al
Vació unió amonia (NH3),
metano (CH4) e hidrogeno (H),
e intento simular las condiciones
de una atmósfera primitiva. Los
calentó, condenso y añadió
descargas eléctricas.
El resultado de este experimento
fue formaldehído, cianuro y otros
cuatro aminoácidos- bloque
fundamental la vida
La mallor parte de los
aminoácidos que se encuentran en
las células hoy en día se peden
haber formada en una atmósfera
primitiva.
Spontaneous generation in a primeval soup: Miller's Experiment
Stanley Miller, a graduate student in biochemistry,
built the apparatus shown here. He filled it with
*
water (H2O
*
methane (CH4)
*
ammonia (NH3) and
*
hydrogen (H2)
*
but no oxygen
He hypothesized that this mixture resembled
the atmosphere of the early earth. (Some are
not so sure.) The mixture was kept circulating
by continuously boiling and then condensing
the water.
The gases passed through a chamber
containing two electrodes with a spark
passing between them.
At the end of a week, Miller used paper chromatography to show that the flask now contained
several amino acids as well as some other organic molecules.
In the years since Miller's work, many variants of his procedure have been tried. Virtually all the
small molecules that are associated with life have been formed:
*
all the amino acids used in protein synthesis
*
all the purines and pyrimidines used in nucleic acid synthesis.