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HISTRIA GEOLGICA DA VIDA

Fernando [email protected]

Departamento de Geocincias Universidade de Aveiro

Campus Universitrio de Santiago

3810-193 Aveiro

Portugal

Tel. +351 234 370357 | Fax. +351 234 370605

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O QUE DIFERENCIA O NOSSO PLANETA DOS DEMAIS DO NOSSOSISTEMA SOLAR?

A existncia comprovada de VIDA superfcie do Planeta

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QUAIS SO AS CONDIES BSICAS PARA A VIDA?

The diversity of life on Earth today is a result of the dynamic interplaybetween genetic opportunity, metabolic capability, environmentalchallenges,[and symbiosis.

For most of its existence, Earth's habitable environment has beendominated by microorganisms and subjected to their metabolism and

evolution.As a consequence of such microbial activities on a geologic time scale, thephysical-chemical environment on Earth has been changing, therebydetermining the path of evolution of subsequent life.For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced fundamental, global changes in the

Earth's environment.
http://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Metabolismhttp://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Cyanobacteriahttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Cyanobacteriahttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Geologic_time_scalehttp://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Metabolismhttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Genetics

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The altered environment, in turn, posed novel evolutionary challenges tothe organisms present, which ultimately resulted in the formation of ourplanet's major animal and plant species.

THEREFORE THIS "CO-EVOLUTION" BETWEEN ORGANISMS ANDTHEIR ENVIRONMENT IS APPARENTLY AN INHERENT FEATURE OFLIVING SYSTEMS.

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Range of tolerance

Extremophiles

Chemical element requirements

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Range of tolerance

The inert components of an ecosystem are the physical and chemical factors

necessary for lifeenergy (sunlight or chemical energy), water, temperature,

atmosphere, gravity, nutrients, and ultraviolet solar radiation protection.

In most ecosystems the conditions vary during the day and often shift from one

season to the next. To live in most ecosystems, then, organisms must be able to

survive a range of conditions, called "range of tolerance.

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Range of tolerance

Outside of that are the "zones of physiological stress," where the survival and

reproduction are possible but not optimal.

Outside of these zones are the "zones of intolerance," where life for that organism

is implausible.

It has been determined that organisms that have a wide range of tolerance are more

widely distributed than organisms with a narrow range of tolerance.

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Extremophiles

To survive, some microorganisms can assume forms that enable them to

withstand freezing, complete desiccation, starvation, high-levels of radiationexposure, and other physical or chemical challenges.

Furthermore, some microorganisms can survive exposure to suchconditions for weeks, months, years, or even centuries.

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Extremophiles

Extremophiles are microbial life forms that thrive outside the ranges life iscommonly found in.

They also excel at exploiting uncommon sources of energy.

While all organisms are composed of nearly identical molecules, evolutionhas enabled such microbes to cope with this wide range of physical andchemical conditions.

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Extremophiles

Characterization of the structure and metabolic diversity of microbialcommunities in such extreme environments is ongoing.

An understanding of the tenacity and versatility of life on Earth, as well asan understanding of the molecular systems that some organisms utilize tosurvive such extremes, will provide a critical foundation for the search forlife beyond Earth.

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All life forms require certain core chemical elements needed for biochemical

functioning.

These include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur the

elemental macronutrients for all organisms often represented by the acronym

CHNOPS.

Together these make up nucleic acids, proteins and lipids, the bulk of living matter.

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Alternative hypothetical types of biochemistry have been proposed which eliminate

one or more of these elements, swap out an element for one not on the list, or

change required chiralities or other chemical properties.

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ORIGEM DA VIDA?

Clay theory

A model for the origin of life based on clay was forwarded by A. Graham Cairns-

Smith of the University of Glasgow in 1985 and explored as a plausible illustration

by several other scientists, including Richard Dawkins.

Clay theory postulates that complex organic molecules arose gradually on a pre-

existing, non-organic replication platformsilicate crystals in solution.

Complexity in companion molecules developed as a function of selection pressures

on types of clay crystal is then exapted to serve the replication of organicmolecules independently of their silicate "launch stage.

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ORIGEM DA VIDA?

Clay theory

In 2007, Kahr and colleagues reported

their experiments to examine the idea that

crystals can act as a source of transferableinformation, using crystals of potassium

hydrogen phthalate.

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ORIGEM DA VIDA?

Clay theory

De facto, no s o habitat da argila

coincide em boa parte com o habitat dos

seresvivos, como tambm se verifica umarelao estreita entre as propriedades mais

caractersticas da argila e dos organismos

vivos e a respectiva interaco com a gua

e o ar.

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ORIGEM DA VIDA?

Clay theory

A argila funciona como um filtro e um

substrato para a vida e, sendo ela,

essencialmente, o resultado da actuao deprocessos qumicos, as suas caractersticas

reflectem a natureza e o grau dos

processos qumicos que presidiram sua

formao em ambientes diversificados,

num passado mais ou menos longnquo ou

mesmo recente.

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ORIGEM DA VIDA?

Clay theory

"Mother" crystals with imperfections were cleaved and used as seeds to grow

"daughter" crystals from solution.

They then examined the distribution of imperfections in the crystal system and

found that the imperfections in the mother crystals were indeed reproduced in the

daughters, but the daughter crystals had many additional imperfections.

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ORIGEM DA VIDA?

Clay theory

For gene-like behavior to be observed, the quantity of inheritance of these

imperfections should have exceeded that of the mutations in the successive

generations, and it did not.

Thus Kahr concludes that the crystals "were not faithful enough to store and

transfer information from one generation to the next.

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ORIGEM DA VIDA?

Clay theory

Cairns-Smith is a staunch critic of other models of chemical evolution.

However, he admited that like many models of the origin of life, his own also

has its shortcomings(Horgan 1991).

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THE EVOLUTIONARYHISTORY OF LIFE

The evolutionary historyof life on Earth tracesthe processes by whichliving and fossilorganisms evolved.

It stretches from the

origin of life on Earth,thought to be over 4,500million years ago, to thepresent day.

The similarities between

all present dayorganisms indicate thepresence of a commonancestor from which allknown species havediverged through the

process of evolution.

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Microbial mats of

coexisting bacteria andarchaea were thedominant form of life inthe early Archean andmany of the major steps inearly evolution are

thought to have takenplace within them.

The evolution of oxygenicphotosynthesis, around3,500 million years ago,

eventually led to theoxygenation of theatmosphere, beginningaround 2,400 million yearsago.

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The earliest evidence of

eukaryotes (complexcells with organelles),dates from 1,850 millionyearsago, and while theymay have been presentearlier, their

diversificationaccelerated when theystarted using oxygen intheir metabolism.

Later, around 1,700

million years ago,multicellular organismsbegan to appear, withdifferentiated cellsperforming specialisedfunctions.

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The earliest land plantsdate back to around 450million years ago,though evidencesuggests that algal

scum formed on theland as early as 1,200million years ago.

Land plants were sosuccessful that they are

thought to havecontributed to the lateDevonian extinctionevent.

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THE EVOLUTIONARY

HISTORY OF LIFE

Invertebrate animalsappear during theVendian period, about

635 million years.

While vertebratesoriginated about 525million years agoduring the Cambrianexplosion.

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DEVONIAN EXTINCTION

The Late Devonian extinction was one of five major extinction eventsin the history of the Earth's biota.

Occurred at the boundary that marks the beginning of the last phase

of the Devonian period, about 374 million years ago.

Overall, 19% of all families and 50% of all genera went extinct.

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DEVONIAN EXTINCTION

Although it is clear that there was a massive loss of biodiversity in theLater Devonian, the extent of time during which these events tookplace is uncertain, with estimates ranging from 500,000 to 25 millionyears.

Nor is it clear whether it concerned two sharp mass extinctions or aseries of smaller extinctions, though the latest research suggestsmultiple causes and a series of distinct extinction pulses through aninterval of some three million years.

Some consider the extinction to be as many as seven distinct events,spread over about 25 million years.

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DEVONIAN EXTINCTION

Previous context

At the end of the Proterozoic, the supercontinent Pannotia had brokenapart in the smaller continents Laurentia, Baltica, Siberia andGondwana.

During periods when continents move apart, more oceanic crust isformed by volcanic activity.

Because young volcanic crust is relatively hotter and less dense thanold oceanic crust, the ocean floors will rise during such periods.

This causes the sea level to rise; large areas of the continents werebelow sea level.

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DEVONIAN EXTINCTION

Previous context

Early Paleozoic climates were warmer than today, but the end of theOrdovician saw a short ice age during which glaciers covered thesouth pole, where the huge continent Gondwana was situated.

Traces of glaciation from this period are only found on formerGondwana.

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DEVONIAN EXTINCTION

Contemporaneous context

During the Late Ordovician ice age, a number of mass extinctionstook place, in which many brachiopods, trilobites, Bryozoa and coralsdisappeared.

These marine species could probably not contend with the decreasingtemperature of the sea water.

After the extinctions new species evolved, more diverse and betteradapted, filling the niches left by the extinct species.

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DEVONIAN EXTINCTION


The Devonian Period (410 to 356 million years ago) has beentraditionally refered to as the "Age of Fishes."

This appelation is appropriate given the dramatic evolutionarychanges in all of the major "fish" lineages during this period.

But this emphasis on fish evolution obscurs other moresignificantchanges.

These changes center on the emergence and diversification of semi-aquatic and terrestrial tracheophytes (vascular plants).

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DEVONIAN EXTINCTION


The continents Laurentia and Baltica collided between 450 and 400Ma, during the Caledonian Orogeny, to form Laurussia.

Traces of the mountain belt which resulted from this collision can befound in Scandinavia, Scotland and the northern Appalachians.

In the Devonian period (416-359 Ma) Gondwana and Siberia began tomove towards Laurussia.

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DEVONIAN EXTINCTION


The collision of Siberia with Laurussia caused the Uralian Orogeny,the collision of Gondwana with Laurussia is called the Variscan orHercynian Orogeny in Europe or the Alleghenian Orogeny in North

America.

The latter phase took place during the Carboniferous period (359-299Ma) and resulted in the formation of the last supercontinent, Pangaea.

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DEVONIAN EXTINCTION


The collision of Siberia with Laurussia caused the Uralian Orogeny,the collision of Gondwana with Laurussia is called the Variscan orHercynian Orogeny in Europe or the Alleghenian Orogeny in North

America.

The latter phase took place during the Carboniferous period (359-299Ma) and resulted in the formation of the last supercontinent, Pangaea.

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DEVONIAN EXTINCTION


By the late Devonian, the land had been colonized by plants andinsects.

In the oceans, there were massive reefs built by corals andstromatoporoids on land.

Euramerica and Gondwana were beginning to converge into whatwould become Pangea.

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DEVONIAN EXTINCTION

Contemporaneous context - synthesis

The world was a very different place in the late Devonian.

The continents were arranged differently, with a supercontinent,

Gondwana, covering much of the southern hemisphere.

The continent of Siberia occupied the northern hemisphere, while anequatorial continent, Laurussia (formed by the collision of Baltica andLaurentia) was drifting towards Gondwana.

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DEVONIAN EXTINCTION


The Caledonian mountains were also growing across what is now theScottish highlands and Scandinavia

The Appalachians rose over America.

These mountain belts were the equivalent of the Himalaya today.

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DEVONIAN EXTINCTION


The biota was also very different.

Plants, which had been on land in forms similar to mosses, liverworts,

and lichens since the Ordovician, had just developed roots, seeds,and water transport systems that allowed them to survive away fromplaces that were constantly wetand consequently built huge forestson the highlands.

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DEVONIAN EXTINCTION

Contemporaneous context - Major environmental changes

From the end of the Middle Devonian, into the Late Devonian, severalenvironmental changes can be detected from the sedimentary record:

widespread anoxia in oceanic bottom waters;

the rate of carbon burial shot up;

benthic organisms were decimated, especially in the tropics and reefcommunities;

high-frequency sea level changes associated with the onset of anoxicdeposits.

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DEVONIAN EXTINCTION

The extinction

The extinction seems to have only affected marine life.

Hard-hit groups include brachiopods, trilobites, and reef-buildingorganisms; the latter almost completely disappeared, with coral reefsonly returning upon the evolution of modern corals during theMesozoic

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DEVONIAN EXTINCTION

The extinction

The causes of these extinctions are unclear.

Leading theories include changes in sea level and ocean anoxia,

possibly triggered by global cooling or oceanic volcanism.

The impact of a comet or another extraterrestrial body has also beensuggested.

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DEVONIAN EXTINCTION

The extinction

Some statistical analysis suggests that the decrease in diversity wascaused more by a decrease in speciation than by an increase in

extinctions.

This might have been caused by invasions of cosmopolitan species,rather than any single event.

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DEVONIAN EXTINCTION

Possible triggers - Bolide impact

Bolide impacts can be dramatic triggers of mass extinctions.

It has been posited that an asteroid impact was the prime cause of

this faunal turnover, but no secure evidence of a specificextraterrestrial impact has been identified in this case.

Impact craters can generally not be dated with sufficient precision tolink them to the event; others dated precisely are notcontemporaneous with the extinction.

Although some minor features of meteoric impact have beenobserved in places (iridium anomalies and microspherules), thesewere probably caused by other factors.

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DEVONIAN EXTINCTION

Possible triggers - Plant evolution

During the Devonian, land plants underwent a hugely significantphase of evolution.

Their maximum height went from 30 cm at the start of the Devonian, to30 m at the end of the period.

This increase in height was made possible by the evolution ofadvanced vascular systems, which permitted the growth of complexbranching and rooting systems.

In conjunction with this, the development of seeds permittedreproduction and dispersal in areas which were not waterlogged,allowing plants to colonise previously inhospitable inland and uplandareas.

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DEVONIAN EXTINCTION

Possible triggers - Effect on weathering

These tall trees required deep rooting systems to acquire water andnutrients, and provide anchorage.

These systems broke up the upper layers of bedrock and stabilised adeep layer of soil, which would have been on the order of metresthick.

In contrast, early Devonian plants bore only rhizoids and rhizomesthat could penetrate no more than a couple of centimetres.

The mobilisation of a large portion of soil had a huge effect; soilpromotes weathering, the chemical breakdown of rocks, releasingions which act as nutrients to plants and algae.

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DEVONIAN EXTINCTION


The relatively sudden input of nutrients into river water may havecaused eutrophication and subsequent anoxia.

Therefore the postulated influx of high levels of nutrients may havecaused an extinction, just as phosphate run-off from Australianfarmers is causing unmeasurable damage to the great barrier reeftoday.

Anoxic conditions correlate better with biotic crises than phases of

cooling, suggesting that anoxia may have played the dominant role inextinction.

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DEVONIAN EXTINCTION


Devonian marine deposits are notable in part for the widespreadoccurrence of black shales in the shallow inland seas of NorthAmerica and Eurasia.

These organic-rich sediments, which indicate anoxic (oxygen-deprived) bottomwaters, occur at about the same time as the multipleextinction events in the Middle and Late Devonian.

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DEVONIAN EXTINCTION

Possible triggers - Effect on CO2The "greening" of the continents occurred during Devonian time.

The covering of the planet's continents with massivephotosynthesizing land plants in the first forests may have reduced

carbon dioxide levels in the atmosphere.

Since CO2 is a greenhouse gas, reduced levels might have helpedproduce a chillier climate.

Evidence such as glacial deposits in northern Brazil (located near the

Devonian south pole) suggest widespread glaciation at the end-Devonian, as a broad continental mass covered the polar region.

A cause of the extinctions may have been an episode of globalcooling, following the mild climate of the Devonian period.

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DEVONIAN EXTINCTION

Possible triggers - Effect on CO2The weathering of silicate rocks also draws down carbon dioxide fromthe atmosphere.

This acted in concert with the burial of organic matter to decrease

atmospheric carbon dioxide concentrations from ~15 to ~3 timespresent levels.

Carbon in the form of plant matter would be produced on prodigiousscales, and given the right conditions could be stored and buried,eventually producing vast coal measures (e.g. in China) which locked

the carbon out of the atmosphere and into the lithosphere.

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DEVONIAN EXTINCTION

Possible triggers - Effect on CO2

This reduction in atmospheric CO2 would have caused global coolingand resulted in at least final period of late Devonian glaciation (andsubsequent sea level fall), probably fluctuating in intensity.

The continued drawdown of organic carbon eventually pulled theEarth out of its Greenhouse Earth state into the Icehouse thatcontinued throughout the Carboniferous and Permian.

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DEVONIAN EXTINCTION

Final synthesis

A variety of causes have been proposed for the Devonian massextinctions, including:

asteroid impacts,

global anoxia (widespread dissolved oxygen shortages),

plate tectonics,

sea level changes and climatic change.

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DEVONIAN EXTINCTION

Final synthesis

One of the more interesting of these is the "Devonian PlantHypothesis".

This theory, first proposed by Thomas Algeo, Robert Berner, J. BarryManard and Stephen Scheckler in 1995, credits the expansion ofterrestrial plants as the ultimate cause for mass extinctions in thetropical oceans.

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DEVONIAN EXTINCTION

Final synthesis

The ramifications of vegetational expansion were dramatic.

These plants transformed the biosphere by transforming theterrestrial environment and linking it more closely with the aquaticrealm.

The first forests created a totally new biome.

Terrestrial invertebrates responded to floral changes.

Soil formation was accelerated and aquatic habitats became more

diverse and stable.

Freshwater and estuarine life became more diverse and productive.

The effects of these plants are also implicated in global carboncycling and the Devonian mass extinction.

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DEVONIAN EXTINCTION

Final synthesis

Ironically, the development and maturation of terrestrial environments

fostered by the expansion of terrestrial plants may have wrecked

havoc on the oceans from which life first arose.

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PERMIANTRIASSICEXTINCTIONEVENT

The PermianTriassic extinction event is the most significant extinction

event.

Affecting mainly marine genera, the PermianTriassic (PTr) extinctionevent, informally known as the Great Dying, was an extinction event thatoccurred 251.4 Ma (million years) ago, forming the boundary between thePermian and Triassic geologic periods.

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It was the Earth's most severe extinction event, with up to 96% of all marinespecies and 70% of terrestrial vertebrate species becoming extinct.

It is the only known mass extinction of insects. Some 57% of all familiesand 83% of all genera were killed.

Because so much biodiversity was lost, the recovery of life on Earth tooksignificantly longer than after other extinction events.

This event has been described as the "mother of all mass extinctions.

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Previous context

With the formation of the super-continent Pangea in the Permian,continental area exceeded that of oceanic area for the first time ingeological history.

The result of this new global configuration was the extensive developmentand diversification of Permian terrestrial vertebrate fauna andaccompanying reduction of Permian marine communities.

Among terrestrial fauna affected included insects, amphibians, reptiles(which evolved during the Carboniferous), as well as the dominant

terrestrial group, the therapsids (mammal-like reptiles).

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Previous context

The terrestrial flora was predominantly composed of gymnosperms,including the conifers.

Life in the seas was similar to that found in middle Devonian communitiesfollowing the late Devonian crisis.

Common groups included the brachiopods, ammonoids, gastropods,crinoids, bony fish, sharks, and fusulinid foraminifera.

Corals and trilobites were also present, but were exceedingly rare.

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A large ( approximately 9), abrupt global decrease in the ratio of 13C to12C, denoted 13C, coincides with this extinction, and is sometimes used toidentify the Permian-Triassic boundary in rocks that are unsuitable forradiometric dating.

Further evidence for environmental change around the P-Tr boundarysuggests an 8 C (14.40 F) rise in temperature, and an increase in CO2levels by 2000ppm (by contrast, the concentration immediately before theindustrial revolution was 280ppm; in October 2010, this concentration was388 ppm, some 108 ppm higher).

There is also evidence of increased ultraviolet radiation reaching the earth,and causing the mutation of plant spores.

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Geologic Evidence of the Permian-Triassic Extinction

Many different geologic aspects of the extinction period have beendocumented recently:1. Salinity in the sea fell sharply during the Permian for the first time,

changing oceanic physics to make deep water circulation more difficult.

2. The atmosphere went from very high oxygen content (30%) to very low(15%) during the Permian.3. The evidence shows global warming AND glaciations near the P-Tr.4. Extreme erosion of the land suggests that ground cover disappeared.5. Dead organic matter from the land flooded the seas, pulling dissolved

oxygen from the water and leaving it anoxic at all levels.

6. A geomagnetic reversal occurred near the P-Tr.7. A series of great volcanic eruptions was building up a gigantic body of

basalt called the Siberian Traps.

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Geologic Evidence of the Permian-Triassic Extinction

Some researchers argue for a cosmic impact at P-Tr time, but the standardevidence of impacts is missing or disputed.

The geologic evidence fits an impact explanation, but it does not demand

one.

Instead the blame seems to fall on volcanism, as it does for other massextinctions.

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