Astrobiology

Lesson 8 Discussion Astrobiology in a nutshell A complete course in Astrobiology deals with the following items:

- Ancient ideas, Copernican revoluon, Enlightenment vs religion - Life beyond the Earth, - Life in the solar system vs life in the Universe as a whole. - Fundamental quesons concerning the origin and evoluon of life on Earth and the implicaons for life in the Universe - Where and how do we search for life outside the Earth? - Intelligent Life (SETI)

But most important: Why should we be interested in “Life in the Universe?” Aer all, We already know that life exist in the Universe! So what is the big deal? (Actual quote) Well....

• Do we have neighbors? It is interesng if somebody lives across the hallway.... • We do not know how life arose on Earth.... • Was it an easy process – and therefore a likely outcome of the condions? • Or was it a difficult process – and therefore unlikely to happen • Astrobiology is a new science – this is how it establish itself? Are we alone in the Universe? The birth of the belief in other worlds

“There are infinite worlds both like and unlike this world of ours…with life lika and unlike” Epicurus (c 300 BC) “There are countless suns and countless earths all rotang around their suns in exactly the same way as the seven planets of our system… The countless worlds “… false and damnable …” in the universe are no worse and G.Galiliei (born 1564) no less inhabited than our Earth”

Giordano Bruno, 1584 in De L'infinito Universo E Mondi

But Aristotele argued that this was NOT the case Today

• “Somemes I think the Universe is full of life and somemes I do not. Either way is equally amazing” – Arthur C. Clarke • “There must be billions and billions of worlds where life arose. Somemes I think there is an Encyclopedia Galacca out there which we have not yet become part of....” – Carl Sagan This has led to the asking of ‘Big Quesons’ like.... “What is the uniqueness of our own Earth?”

“Are we (lifeforms) alone?”

“What is our past & future?” - The formaon of planets - The evoluon of planetary systems Cosmic Vision is centered around four Grand Themes: 1. What are the conditions for planet formation and the emergence of life? • From gas and dust to stars and planets • From exo-planets to biomarkers • Life and habitability in the Solar System 2. How does the Solar system work? 3. What are the Fundamental Physical Laws of the Universe? 4. How did the Universe originate and what is it made of? Cosmic Vision is centered around four Grand Themes: 1. What are the conditions for planet formation and the emergence of life? • From gas and dust to stars and planets • From exo-planets to biomarkers • Life and habitability in the Solar System 2. How does the Solar system work? 3. What are the Fundamental Physical Laws of the Universe? 4. How did the Universe originate and what is it made of?

First: In-depth analysis of terrestrial planets. Next: Understanding the conditions for star & planet formation, and the origin of life. Later: Census of Earth-sized planets, exploration of Jupiter’s moon Europa. Finally: Image terrestrial exoplanet.

The realisaon that for the first me in history we can do more than speculate Life beyond the Earth?

• There is a great general interest in the queson: – Viz. Films, TV, UFO’s, Persistent rumours about Area 51, etc. • But also sciensts are interested for a number of reasons: – We do not really know how life arose on the Earth – We do not know what the role of life in the Universe is – We do not know many of the evoluonary stages on Earth • It is clear that the discovery of any kind of life outside the Earth would have an enormous impact Life beyond the Earth?

• So what are we going to look for: – The intelligent life portrayed in films like Startrek? Or ourselves? – Giraffes, Platypus or Hamsters? – Simple one cellular life like that inhabing our Earth for most of its history? ~4Gyrs • All of the above – The history of life on our Earth makes that clear. Modeled on our own experience • Caveat: Somehow we will have to address the queson that life could be very different (Oblivion) Astrobiology

• So Astrobiology is the study of the origin, evoluon, distribuon and future of life in the whole Universe • How can it be addressed? – By study the events that took place on the Earth, by searching for signs of life on the planets in the Solar System, by searching in the rest of the Universe – By using cross disciplinary methods including everything from geophysics to SETI Astrobiology is a new science - how does it establish itself? Astrobiology

Ÿ By demonstrang its value to understand life on Earth and its evoluon

Ÿ By demonstrang how we can understand the past and future evoluon of the Solar System

• By clarifying, eventually, one of the great quesons: Are we alone in the Universe? Life beyond the Earth?

• But the issues are centered when considering life on the Earth itself and its origin • We do not know when or how life arose on Earth • We know very lile about the evoluon of life for the first ~ 4 Gyrs • We do not know why aer ~ 4 Gyr we had the “Cambrian Explosion” leading to all phyla that exist on Earth today How can science help us answer the fundamental quesons concerning where life comes from and how it is formed? First we consider life on the Earth?

• Three important quesons: • What is life? • When did life begin on the Earth? • And how did life arise on the Earth? What is life (Clausius, 1865)

• Clausius formulated the first two laws of thermodynamics • 1: The energy of the Universe is constant • 2: The entropy (degree of disorder) of the Universe tends to a maximum • Boltzman speculated: “ The general struggle for the existence of animate beings is not a struggle for raw materials, nor for energy, but for negave entropy, available by the transion of energy from the hot Sun to the cold Earth What is life Schrödinger’s paradox(1944)

• In a world governed by the 2nd law of thermodynamics isolated systems are expected to tend to a state of maximum disorder. • Life approaches and maintains a highly ordered state – does this violate the 2nd Law. A paradox? • Life is not an isolated system è no paradox. Why not? • The increase of order inside an organism is compensated more than enough by the increase in disorder outside this organism. The highly ordered state, is sustained by causing a net increase in disorder in the Universe. • The complexity on Earth caused by life requires energy mostly provided by the Sun and supernova (radioacvity) è increases entropy more than life diminish it What is life Schrödinger’s paradox(1944)

• So we live in close connecon with the Universe and not separate from it in any way • Later we will see this again when discussing photosyntheses and how this connect life on Earth with the Sun • Is the Universe intended for life? This is a big issue in Cosmology • Parallel Universes with different natural laws (an infinite amount) solve this issue A brief history of life

• All life on Earth is probably related and goes back to a “first cell” ~ 4 Gyrs ago • The oldest fossils are probably (the stromatolites) simple one- cellular with no nucleus (~ 3.5 Gyr). Procaryotes • 2 Gyrs cells with a nucleus evolved. Eucaryotes • Mulcellular life are known from 650 – 542 Myrs ago. The first signs are fossilised tracks of wormlike life • 542 Myr Cambrian explosion (The Burgess shale) • Organisms with shells and (exo-)skeletons appear • First Vertebrates (488-416 Myr ago Ordovicium), Jawless fish A brief history of life

• First plants on land not later than 444-416 Myr ago (Silur) • First frogs 416-359 Myr ago (Devon) • First mammals 251-200 Myr ago (Trias) • First primates (end of Cretaceus) 66 Myr ago • Separang from our cousins (Chimpanzees) 7-6 Myr ago • Homo Erectus ~ 1 Myr – 143Kyr ago • Homo Heidelbergiensis (the brightest of the lot), Neanderthalensis, Denisovans 800Kyr – 40 Kyr • Homo Sapiens 200 Kyr - ..... In order to have life, we first need a planet

Observations of forming stars demonstrate that this happens in dense clouds of atomic and molecular gas observed in the Milky way and other galaxies Stars, planets and the Interstellar Medium (ISM)

Observaons show formaon on both galacc and intergalacc scales

The Interstellar medium – the cradle of Planets and life(?)

As far as we know, life must begin with complex organic molecules

Such molecules can form on a planetary surface but also in interstellar space

~ 10% of the (visible) mass of the Galaxy consist of gas and dust between the stars and half of this mass is in molecular form

Significant amounts of this gas is found in dense clouds and these are the precursors of stars and planets The Interstellar medium – the cradle of Planets and life(?)

Stars and planets thus form embedded in a gas consisting partly of organic molecules – i.e. Molecules built with Carbon atoms

Molecules similar to nucleotides, fatty acids, carbohydrates and amino acids

è Prebiotic molecules are found all over the universe

But processes forming interstellar molecules are different from those occurring on the Earth The Interstellar medium – the cradle of Planets and life(?)

Buckminster-Fullerene C60 Crab supernova remnant (1054 A.D.), creating heavy elements, ejecting them into interstellar medium Stars form in clusters

• Most molecular clouds contain between 104 and > 106 solar masses of gas. • There is thus enough to form a large amount of stars in each cloud The Interstellar medium – the cradle of Planets and life(?)

In the interstellar gas are found Polycyclic Aromatic Hydrocarbons (PAHs). Consist only of Carbon and Hydrogen in multiple rings

It has been observed that PAH’s in space transform through hydrogenation, oxygenation and hydroxylation è Organics

è Formation of amino acids and nucleotids è may form è Proteins and DNA respectively We know about 145 different molecules that have been detected (almost exclusively in the micro wave region – mm and sub-mm λ) in the interstellar medium

But most important è ISM leads to Stars and planets The formaon of the Sun and Planets in the Solar System

• First step towards life was the formaon of the Earth • Condions on Earth at formaon are important to try to form a picture of how life first appeared • The starng point was a dense molecular cloud consisng of gas and dust • Relavely high density • Rotang – containing angular momentum • Contracng – converng potenal energy to kinec energy The formaon of the Sun and Planets in the Solar System • The accreng gas formed a disk of varying composion • Formaon of clumps • Metal rich elements formed grains of iron, nickel, refractory materials in inner part • Grains consisng of ices further out beyond ‘snow line’ • Metals originate in stellar wind of red giant stars and in supernova explosions • Supernova may be part of process starng collapse of dense ISM clouds • The Sun became hoer and hoer • High density • Rotang – containing angular momentum • Contracng – converng potenal energy to kinec energy The formaon of the Sun and Planets in the Solar System

• Angular momentum and Energy was conserved • Faster rotaon • Higher temperature • Concentraon to center (99.8% of mass) èFormaon of the Sun • The Sun was now a T-Tauri star. Variable. Finally, contracon è density and temperature in the center are high enough for nuclear reacons to begin. • Large amounts of energy released • Contracon balanced by release of nuclear energy H è He • Sun becomes stable and the solar surface becomes cooler (~ 25% cooler than today) è “faint young Sun”. • The Solar radiaon becomes eventually stronger because the Sun (its core) becomes more compressed and hoer as the center is filled with He The formaon of the Sun and Planets in the Solar System • The clumps in the surrounding disk now form the planets. • Clumps merge and contract grains è pebbles è boulders è planetesimals è planets • The Earth now became very hot (1000K?) through contracon and solar radiaon • Too high temperature for ices and other volales at Earth’s distance from the young Sun • Earth and inner planets form in a region with Fe, Ni, simple minerals (refracve) as SiO and MgO çè Just a small fracon of gas disk mass • Further out (beyond the “snow line”) planets form from H,

He, Ne, H2O, molecules with C, N form larger planets (more gaseous material present) The formaon of the Sun and Planets in the Solar System

• Time frame a few mes 107 years(?) • Many more planets formed – some ejected, some merged with the Sun? • Dynamical interacon between large planets • Voids and large aggregates of small planetesimals interact and collide • E.g. The “Nice model” • The Nice model is a scenario for the dynamical evoluon of the early Solar System • It suggests that the migraon of the giant planets from a more compact arrangement aer the dissipaon of the gas in the system lead eventually to the current configuraon which is stable of many billions of years The formaon of the Sun and Planets in the Solar System

• The Nice model • Formulated by Morbidelli, Leavison and co-workers (2006)

• Dynamical calculaons explain historical events like • the Late Heavy Bombardment (+800 Myr), • The change of places of Neptune and Uranus (+1Gyr) • the formaon of the Oort cloud • The formaon of the Kuiper-Edgeworth belt • The formaon of the Jupiter and Neptune Trojans • The formaon of the trans-Neptunian Objects (Pluto, etc) The formaon of the Sun and Planets in the Solar System

• The Nice model

Simulation showing the outer planets and planetesimal belt: a) early configuration, before Jupiter and Saturn reach a 2:1 resonance; b) scattering of planetesimals into the inner Solar System after the orbital shift of Neptune (dark blue) and Uranus (light blue); c) after ejection of planetesimals by planets The formaon of the Sun and Planets in the Solar System • The formaon of Earth’s Moon • The Moon is thought to have formed nearly 4.57 billion years ago, not long aer Earth • There are several hypotheses but most accepted is that the Moon formed from debris of the impact on Earth by a Mars sized body

This has been observed recently in the case of HD172555 The formaon of the Sun and Planets in the Solar System • In the outer reaches of the solar system large numbers of small bodies (total mass is rather low) are formed and probably ejected halfway to the nearest stars (Oort cloud, containing primoridal maer)

• These bodies consist of H, He, H2O and CH4. • The right environment to form pre-bioc compounds with O, C and N

67P/Churyumov–Gerasimenko The evoluon of the young Earth

• The young Earth was built by minerals (from dust grains). • Originally it was very hot on the surface (~1000K) but eventually the gravitaonal contracon along with the heat from radioacve heavy metals heated the central parts • These became elasc and eventually fluid such as it is today. All heavy elements chiefly Fe and Ni sank to the center and formed a core è Increased the temperature. • Connental plates may have formed early (solid rock floang on an elasc medium) • Remnants of the formaon of the Solar System collided regularly with the planets and brought substances that did not exist originally in our part of the solar system (Water and Carbonic compounds) Further (possible) evoluon of the young Earth

• Part of the ancient Earth would have been disrupted by the impact creang the Moon which should have caused melng of one or two large areas. Present composion does not match complete melng and it is hard to completely melt and mix huge rock masses • However, a fair fracon of material should have been vaporized by this impact, creang a rock vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving

behind hot volales which probably resulted in a heavy CO2 atmosphere with H and H2O • Liquid water oceans existed despite the surface temperature of 230 °C

because of the atmospheric pressure of the heavy CO2 atmosphere (60 bar) • As cooling connued, subducon and dissolving in ocean water removed most CO Geological ming

• How can we date the stages in the early evoluon of our planet? • Mainly using radioacves. Mostly the Uranium-Lead chain of decay • The Uranium-Lead radiometric dang scheme today è an error margin in rocks that < two Myr in 2 1/2Gyr • There are no rocks on Earth older than 3.8 Gyr. But when one analyse

Zircon (ZrSiO4 crystals) a different result emerges. Zr incorporates U in its crystals but reject lead • Two chains: 1) from 238U to 206Pb, with a half-life of 4.47Gyrs and 2) from 235U to 207Pb, with a half-life of 704 million years. • This gives an age of the Earth’s Zr crystals of 4.4 Gyrs • The Moon is less changed than the Earth è 4.57Gyr which is similar to meteorites originang in the asteroid belt Geological ming

• We therefore divide the early phases of the Earth’s history into • 1. Hadean from the beginning unl ~3.8 Gyr • 2. The Archean from 3.8 Gyr unl ~ 2.4 Gyr • The Lunar landings in the 1970:es brought in-situ measurements of the Moon. It was found that the “Mare” the large lava plains on the Moon were all formed by heavy collisions ~ 4 Gyrs ago. The conclusion was that a number of bodies > 100km in diameter collided with the Moon during this epoch (see the Nice model for explanaon) • The Earth, being bigger, must have been hit much more and each collision is large enough so that most of the rocks surface of the earth would have melted or even turned into gas. Most of the water must have turned into steam è The implicaons for life if it has formed already are not good. • These interpretaons are not totally accepted! • What is clear is that rocks dated at 3.8 Gyrs demonstrate that the collisions ceased then. Structure of the young Earth

The early phases of the Earth was violent even when the bombardment had ceased

Major movements in the crust, tectonics, as well as severe volcanic activity

Large amounts of radioactivity è heating + contraction + latent heat left from the merger of the planetesimals. + the bombardment Volcanic activity takes place at the border This led to a stratification that remains to this day between different tectonic plates, where magma can reach the Crust (~ 35km – thinner under the oceans, thicker under surface land) + Mantle (3000km) consisting of MgO+ Core (Fe+Ni) down to 6400km Under the mantle is the Magma which is liquid Tectonic plates Traces of early life on Earth

• We can not really expect to find traces of the first life on Earth since it was very simple and primive and our planet have been re-cycled • Early evoluon appear, however, to have produced micro organisms that used Sunlight gave traces in the fossil record that can be found aer 3 Gyr. • Cyano bacteria formed very early and dominated the Earth for at least 1 Gyr. They produced free oxygen and thus changed the Earth’s atmosphere • Some researchers claim that fossil traces of Stromatolites exist that are 3500 million years old. These are colonies of cyanobacteria which produce mineralised mats that sll exist

Fossilised stromatolite Early Life on the Earth? – What do we know

• The Earth formed about 4.54 Gyr ago • Earliest undisputed (almost) signs of life are fossil microbial mats (Stromatolites) from 3.48 Gyr (Australia) • Biogenic(?) Graphite in sedimentary? 3.7 Gyr old rocks in Greenland • Two other studies find signs (from fossil 12C/13C raos) from 4.25 and 4.4 Gyr • è Life arose Early? Implicaons? The atmosphere of the young Earth

• Aer the nuclear reacons lit of inside the Sun its luminosity,LO, dropped. Observaons of T-Tauri stars indicate the LO may have gone down by 25-35% • The Zircone analysis indicate early liquid water on the Earthè a much denser atmosphere with “greenhouse gases” (CO, CH4) • The atmosphere probably originated in planetesimals/comets falling down on to Earth, but also outgassing (volcanos) since such components must

have been part of the formaon è H combining with O, C, N è H2O, CH4, NH3 • This is a reducing atmosphere with completely different properes than in our present atmosphere which is oxidizing. • Reducing atmosphere does not form oxides (e.g. Rust with Fe), C+H does

not explode but instead form CH4.

• H is to light to stay in the Earth’s atmosphere. H2O and NH3 are dissociated by UV light and the H escapes to space which leads to an atmosphere

dominated by N (78.09% today), (+ 20.95% O, 0.93% Ar, 0.039% CO2). Differences between a young Earth and a young Venus • The two planets are very similar in size and in composion but Venus has a temperature ~ 600K, while the Earth is between 273K and 370K (average 287.3K in 2013). – The black body temperature of Earth is 254K or -19 degrees C. IT is the green house effect that keep Earth from being a snow ball again • The current density of Venus atmosphere is 90 mes higher than the Earth’s • Their atmospheres were very likely similar to start out with....But Venus was always hoer than the Earth èVenus lost more of its water and

therefore never got plate tectonics. The H escaped and O reacted with CH4 and formed CO2 which made the planet hoer. All its C is today in the atmosphere

• On Earth most of the CO2 formed in this way is dissolved into the oceans, and together with Ca goes out of soluon as carbonates. Stanley Miller’s experiment

• A. Oparin (1894-1980) suggested in 1920:es that a reducing atmosphere with H and hydrogenated molecules together with electric discharges and Uv radiaon è chemical reacons important for the chemistry of life. • Harold Urey (1893-1981, Nobel prize in 1934, discovery of D) suggested an experiment to his student Stanley Miller (1930-2007) which he carried out in 1953 • He created reducing atmospheres in the lab and passed electric discharges through it • Aer a few days he found some black goo in the test vessel: – Asparc acid and Butyric acid – no surprises there. – The second most common substance, however, was glycin the simplest amino acid – And number 4 was alanin another important amino acid + some more amino acids in significant amounts And amino acids are the building blocks of proteins! è Biochemestry! Stanley Miller’s experiment

• Problem is of course that we already found that the Earth would lose its H,

H2 and rapidly get an atmosphere of N2 and CO2 which does not allow the results of Miller’s experiment • Miller connued to work for the rest of his life and other ideas have been tested:

– Methane ejected from volcanos into a CO2 rich atmosphere gives some amino acids but not in such great amounts – Modern calculaons indicate that the Earth would have been losing its H much slower than previously suggested è Life could have had me to start • A reducing atmosphere and cold seas/oceans seem to be a starng point for creang an environment into which the building blocks of life could

have been formed. A lot of CH4 is also required plus suitable energy sources • Compared to other alternaves including the present Earth, these condions could be searched for around exoplanets with advanced instruments and it would help if the planet was larger than the Earth

(more H and H2 is retained) èSuper Earth How did the first life arise on Earth?

• Summary: It is at least possible that the condions of Miller’s experiment, together with cold oceans of

H2O could have existed for a significant me Life or its building blocks arriving from space?

• The Murchison meteorite fell in daylight over Murchison, Victoria, Australia on 28/9 1969. It was widely observed as a fireball, breaking into at least 3 fragments as it was observed and an impact tremor was felt • 100 kg of mass was collected in fragments of up to 7kg over an area of 13 km2 including one inside a barn • Over 15 amino acids plus a host of other organic components have been idenfied. Amounts are similar to those found in the Miller experiment • So far no organic compounds have been retrieved from a comet, but observaons of Halley’s and other comets have demonstrated the presence of carbonic compounds such as hydrogen cyanide and formaldehyde. Also adenine, one of the bases in nucleic acids (like DNA) was seen in Halley • In just a few weeks, ESA will release data from a laboratory landed on the comet 67P/Churyumov–Gerasimenko