Capitulo 1: El Origen de la Vida

• En una clase de la Historia de la Vidacomenzamos discutiendo su origen.

• Sabemos que existe vida en nuestro planetapero no sabemos donde y como se origino.

• No tenemos evidencia de vida en ningunaotra parte de nuestro universo.

• Debemos suponer que la vida, como laconocemos, se origino en este planeta.

Capitulo 1: El Origen de la Vida• Existen moléculas orgánicas complejas enel espacio, cometas, meteoritos etc..

• Estas son el resultado de gas interestelarexpuesto a radiación cósmica y estelar.

• Estas probablemente se estrellaban contra elplaneta Tierra en ocasiones, siendo así unafuente de moléculas orgánicas.

• Sin embargo este proceso no resultara en eldesarrollo de la vida. Además en nuestroplaneta también se pueden formarmoléculas orgánicas.

• Para determinar como comenzó la vida ennuestro planeta podemos reconstruir comose formo nuestro sistema solar y nuestroplaneta.

• Con la ayuda de los biólogos podemosentonces tratar de reconstruir el origen de lavida.

• La vida como la conocemos esta compuestamayormente por agua en su estado liquido.

• No podemos imaginarnos que exista vidasin agua, por lo cual necesitamos planetascon agua (océanos) para crear vida.

Origen de Nuestro Sistema Solar• Los astrónomos creen que el universo tiene

15 billones de años de antigüedad. Losprimeros elementos comenzaron a formarse(hidrógeno y helio).

• Fuerzas gravitacionales colapsaron nubes deestas partículas para formar estrellas.

• El 99% de las partículas se unieron paraformar estrellas (el sol).

• Un 1% de este polvo estelar quedo en orbitaalrededor del sol.

Los planetas

• Partículas de polvo tienden a unirse porfuerzas electroestáticas en un procesoconocido como “acreción”:– Ej. Mota de polvo debajo de sus camas.

• Planetas pequeños se pueden haber formadode la misma manera cuando las partículasde polvo, en orbita alrededor del sol, seunieron.

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 estadoLiquido.

• Cada uno de estos cuatro planetas comenzócomo una masa de material derretido comoresultado de los choques entre planetas maspéguenos que los formaron.

• Eventualmente su capa exterior se enfrío yformo una corteza.

• Una ves se enfrío la superficie de losplaneta, la temperatura exterior del planetadepende por completo de la distancia del soly de los gases volcánicos que salen a lasuperficie 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 resultaen gases atmosféricos que producen unaatmósfera y el efecto de casa deinvernadero.

• Un planeta pequeño no puede retener losgases en su atmósfera debido a un campogravitacional débil.

Mercury Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; ithas no plate tectonics.

Mercury actually has a very thinatmosphere consisting of atoms blastedoff its surface by the solar wind.Because Mercury is so hot, these atomsquickly escape into space. Thus incontrast to the Earth and Venus whoseatmospheres are stable, Mercury'satmosphere is constantly beingreplenished.

Venus

VenusVenus, the jewel of the sky, was once know by ancient astronomers as themorning star and evening star. Early astronomers once thought Venus to betwo separate bodies. Venus, which is named after the Roman goddess of loveand 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 outof the same nebula. However, during the last few years scientists have foundthat the kinship ends here. Venus is very different from the Earth. It has nooceans and is surrounded by a heavy atmosphere composed mainly of carbondioxide with virtually no water vapor. Its clouds are composed of sulfuric aciddroplets. At the surface, the atmospheric pressure is 92 times that of the Earth'sat sea-level.

Venus is scorched with a surface temperature of about 482° C (900° F). Thishigh temperature is primarily due to a runaway greenhouse effect caused by theheavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere toheat the surface of the planet. Heat is radiated out, but is trapped by the denseatmosphere and not allowed to escape into space. This makes Venus hotter thanMercury.

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 inthe west and set in the east.

La Luna

No hay agua, no hayevidencia de agua enestado liquido en elpasado y no hay vida.

MarsMars is the fourth planet from the Sun and is commonly referred toas the Red Planet. The rocks, soil and sky have a red or pink hue. Thedistinct red color was observed by stargazers throughout history. Itwas given its name by the Romans in honor of their god of war.Other civilizations have had similar names. The ancient Egyptiansnamed the planet Her Descher meaning the red one.

Before space exploration, Mars was considered the best candidate forharboring extraterrestrial life. Astronomers thought they sawstraight lines crisscrossing its surface. This led to the popular beliefthat irrigation canals on the planet had been constructed byintelligent beings. In 1938, when Orson Welles broadcasted a radiodrama based on the science fiction classic War of the Worlds by H.G.Wells, enough people believed in the tale of invading Martians tocause a near panic.

Another reason for scientists to expect life on Mars had to do withthe apparent seasonal color changes on the planet's surface. Thisphenomenon led to speculation that conditions might support abloom of Martian vegetation during the warmer months and causeplant life to become dormant during colder periods.

Ophir Chasma is a large west-northwest-trending trough about 100 km wide. TheChasma is bordered by 4 km high walledcliffs, most likely faults, that show spur-and-gully morphology and smoothsections. The walls have been dissectedby landslides forming reentrants; one area(upper left) on the north wall shows ayoung landslide about 100 km wide. Thevolume of the landslide debris is morethan 1000 times greater than that from theMay 18, 1980 debris avalanche fromMount St. Helens. The longitudinalgrooves seen in the foreground arethought to be due to differential shear andlateral spreading at high velocities. Thelandslide passes between mounds ofinterior layered deposits on the floor ofthe chasma. (Courtesy USGS)

In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealedwas a surface containing many craters and naturally occurring channels but no evidence ofartificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2touched down on the surface of Mars. The three biology experiments aboard the landersdiscovered unexpected and enigmatic chemical activity in the Martian soil, but provided noclear 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 solarultraviolet radiation that saturates the surface, the extreme dryness of the soil and theoxidizing nature of the soil chemistry prevent the formation of living organisms in the Martiansoil. 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 didprovide a precise and definitive analysis of the composition of the Martian atmosphere andfound previously undetected trace elements.

No hay agua en estado liquido

Evidencia de canales naturales.

Atmosphere

The atmosphere of Mars is quite different from that of Earth. It is composed primarily ofcarbon dioxide with small amounts of other gases. The six most common components of theatmosphere 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 amountcan condense out, forming clouds that ride high in the atmosphere or swirl around the slopesof towering volcanoes. Local patches of early morning fog can form in valleys. At the VikingLander 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 waterto flow on the planet. Physical features closely resembling shorelines, gorges, riverbedsand 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 of20° 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 millionmiles). It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for theEarth rotate a complete revolution. It has a diameter of 12,756 kilometers (7,973 miles), only afew hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percentnitrogen, 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 spinand molten nickel-iron core give rise to an extensive magnetic field, which, along with theatmosphere, shields us from nearly all of the harmful radiation coming from the Sun andother stars. Earth's atmosphere protects us from meteors, most of which burn up beforethey can strike the surface.

From our journeys into space, we have learned much about our home planet. The firstAmerican satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allenradiation belts. This layer is formed from rapidly moving charged particles that are trapped bythe Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findingsfrom satellites show that our planet's magnetic field is distorted into a tear-drop shape by thesolar wind. We also now know that our wispy upper atmosphere, once believed calm anduneventful, seethes with activity -- swelling by day and contracting by night. Affected bychanges in solar activity, the upper atmosphere contributes to weather and climate on Earth

• El planeta Tierra tiene el tamaño adecuado; no seha enfriado en su interior lo que resulta enactividad volcánica que lleva gases a la atmósferacontinuamente.– Erupción volcánica en Kilauea, 50% vapor de agua

• También tiene, como resultado de su tamaño, unaatmósfera que atrapa los gases (continuamente losgases escapan de nuestra atmósfera).

• El planeta tierra se encuentra a una distanciaadecuada del sol para que el agua se encuentre ensus estados sólido, liquido y gaseoso.

Reconstruyendo el origen de laVida

En nuestro planeta, una atmósfera primitivabañada de luz ultravioleta del sol, resultaríaen gases que se disolverían fácilmente enagua enriqueciendo el océano con carbón.Estos gases serian amonia (NH3), metano(CH4), y monóxido de carbono (CO).

Reconstruyendo el origen de laVida

• Uno de los productos químicos de lacombinación de estos productos seriacianuro (HCN).

• Este es uno de los bloques básicos en laconstrucción de moléculas orgánicas mascomplejas.

Stanley Miller

• Miller, en la Universidad de Chicagodecidió reconstruir como seria unaatmósfera primitiva para ver que reaccionesquímicas ocurren y sus resultados.

Miller, en un espacio sellado alVació unió amoniaamonia (NH3), (NH3),metano (CH4) e hidrogeno (H),metano (CH4) e hidrogeno (H),e intento simular las condicionesde una atmósfera primitiva. Loscalentó, condenso y añadiódescargas eléctricas.

El resultado de este experimentofue formaldehído, cianuro y otroscuatro aminoácidos- bloquefundamental la vida

La mallor parte de losaminoácidos que se encuentran enlas células hoy en día se pedenhaber formada en una atmósferaprimitiva.

At the end of a week, Miller used paper chromatography to show that the flask now containedseveral 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 thesmall 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.

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 resembledthe atmosphere of the early earth. (Some arenot so sure.) The mixture was kept circulatingby continuously boiling and then condensingthe water.

The gases passed through a chambercontaining two electrodes with a sparkpassing between them.