Astrobiology

Prepared by Tereza Varnalı for SCI 102 ‘ultra deep field’ view Hubble Space

Telescope nearly 10,000 galaxies across the observable Universe.

Astrobiology tries to understand

Life in the context of the Universe •Very difficult to define life (no natural definition ie. water-H2O)

Approach: (ask questions)

What is it made of? What does it need? What does it do? • C N H O N P S (elements of life),Ca, Mg • energy, water, a body based on organic C, adapatation strategies for survival, leave offsprings, continuity, metabolism, mutation. • Creates negative entropy, disequilibrium in atmosphere, radioisotope fractionation 12C/13C What are characteristics of life that we could list?

For example, life exhibits complex behaviour and often unpredictable interactions. Life grows and reproduces. Life also metabolises.

However, the problem with all these characteristics individually is that many non-biological entities exhibit these behaviours. Salt crystals, when exposed to the appropriate conditions, such as a saturated salt solution, can grow. Fires, in a way, ‘metabolise’ organic material. They burn organic C (trees) in O2 (air) to produce waste products, CO2 and H2O. The chemical reaction involved in this process is identical to respiration used to produce energy in animals. The only difference is that the reaction is biochemically controlled in life and uncontrolled in fires. computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself or infecting other computer programs . We can develop working definitions of life that are adequate for astrobiology.

It may never be possible to find a ‘final’ definition of life. Diversity of life on modern earth Tree of life, showing domains of life / based on comparing sequences of rRNA

Prokaryotes Prokaryotes / bacteria / bulk diversity

Physiological & Metabolic diversity Allow life to inhabit every possible place on earth even on the floor of the ocean around hydrothermal vents in hot springs in acidic / basic conditions in Antarctica in deserts... all teeming with microorganisms Another way to conceptualise the biosphere is to consider its tolerances to physical and chemical extremes. We can view all organisms to be within an enormous biological zoo surrounded by a fence. The fence is a set of physical and chemical extremes beyond which life cannot adapt – a fence that separates life from death.

A simplified depiction of the biospace. There are many more extremes that define the limits of life than those shown here. These limits could be defined for survival, metabolic activity (growth) or reproduction.

Limited by what we understand about life. Extremophiles (from the Greek word philos or love) :These are organisms that not merely tolerate extremes but have biochemical adaptations that require them to grow under given extremes.

Extremotolerant organisms: These are organisms not optimally adapted to growth in extremes, but have the capacity to grow in them.

We find that the edges of the biospace are dominated by microbes. As conditions become more extreme it becomes difficult to modify the entire biochemistry of complex multicellular organisms with their multiple cell type. Single-celled microbes have an advantage to adapt. Many record holding extremophiles are Archea, but are found in three domains of life.

Thermophiles: if their optimal growth range is 45 – 80 °C / hyperthermophiles if they have an optimal growth temperature above 80 °C.

Methanopyrus kandleri (archaea) grows & reproduces at 122 o C (present upper limit), Pyrolobus fumarii (archea) growth range 90 - 113 o C , both from black smoker.

Cold-loving microorganisms are known as ‘psychrophiles‘ or cryophiles’, with an optimum growth temperature of less than 15 °C. The precise lower T limit is unknown; the current limit : for reproduction is -15 ° C ; for metabolic activity is -25 °C.

Halophiles (Salt-loving organisms) need to grow in salt concentrations of 15 – 37% NaCl. Mariana Trench (10,900 m depth)

Acidophiles inhabit extremes of pH usually below pH 3.

RioTinto in Spain, with a pH value around 2.

Alkaliphiles inhabit extremes of pH usually > pH 9.

Mono Lake in California, is an enclosed lake ~760,000 yrs old. Salts accumulate within the enclosed lake and the result is a shallow water environment with a pH of 10. The piezophilic or barophilic microorganisms inhabit high pressure environments. Organisms that are tolerant to radiation, but do not require it to grow are radiotolerant.

Doses of 10,000 Gray (Gy) can be tolerated by the bacterium Deinococcus radiodurans.

Chroococcidiopsis, a photosynthetic cyanobacterium / lives in rocks in cold and hot deserts /other environments / can tolerate 15, 000 Gy .

To get some perspective, 5 Gy of equivalent ionizing radiation is sufficient to kill a human. Another way in which life can deal with extreme conditions on a planetary surface is to occupy habitats which provide shelter from extreme conditions such as rocks (geo-strategy).

Chroococcidiopsis and other microbes inhabit rock (porous). Polyextremophiles: To understand limits of life truly, the polyextremophiles must be investigated.

Eukaryotic extremophiles

The smallest animals with resistance to extremes are the tardigrades (water bears ~0.5 mm) / found throughout the world / including in polar regions, equatorial deserts and high mountains /date back to over 500 mil.yrs ago. Tardigrades can be heated for a few minutes to 151 °C or cooled to −200 °C. They can withstand vacuum and more than 1,200 times atmospheric P. Some species can even withstand a pressure of 6,000 atm, six times the pressure of water in the deepest ocean, the MarianaTrench. Geological Time

Co-evolution of life and the planet

GOE Glaciations Continents /Supercontinent Cambrian explosion Extinctions Our own species It is not known when the human primate lineage first used tools. Evidence suggests that Homo habilis used pebbles as tools ~2.3 million years ago and this marks the beginning of the Paleolithic (The ‘Stone Age’), which ran through until the beginning of the last ice age 10,000 years ago.

‘Archaic’ Homo sapiens, the forerunner of modern humans, is thought to have evolved between 400,000 and 250,000 years ago and was using stone tools.

About 50,000 years ago , Homo sapiens began to engage in distinctly more complex and modern behaviour, including cave painting, burying dead, making specialist tools and jewellery. detecting planets orbiting other stars / exoplanets

Ultimate aim: evidence of life on distant planets

Transit method

Doppler method Keppler Mission As with all species, humans face a number of threats. Some of these are natural threats. Some of these threats are:

 Supervolcanoes  Asteroid and comet impacts  Disease

As a civilization emerges, extracts resources and generates waste gases from various processes, it is likely that this activity may become extensive enough tobe self destructive. The discovery of the destruction of the UV-screening ozone layer (the so-called ‘ozone hole’) in the stratosphere by chlorofluorocarbons (CFCs) used in spray cans and refrigerators, led to the internationally agreed Montreal Convention, signed in 1987, to ban the use of these substances. Since that time, concentrations of CFCs in the atmosphere have begun to decline.

From an astrobiological perspective, the Montreal Convention illustrates one important point – that an intelligent species can develop a planetary-scale awareness of its impact on the home world and implement policies to reverse the damage. It is not the case that technological species with incredible capacity to manipulate their environment are doomed to cause irreversible destruction to their planet. Unfortunately, there are many gases and waste products that a technological civilization can produce. In our own case, increases in the concentrations of CO2 is attributed to the burning of fossil fuels. increases in CO2 / enhances the greenhouse effect / melting of ice sheets and glaciers / an increase in sea levels / changes in the ranges of organisms as they begin to respond to changing temperatures and atmosphere. The effects of climate change are uncertain. However, more chaotic weather systems, water shortages, major impacts on agricultural productivity and other knock-on effects have been predicted.

Need to generate planetary-scale agreement on how to manage planetary atmosphere. Our civilisation is a relatively recent biological phenomenon, but it yields insights into the co-evolution of intelligence and its planetary environment.

Humans have long had aspirations to leave the Earth / first Yuri Gagarin (1934-1968) made the first orbit of the Earth in the Vostok spacecraft in 1961 / in 1969 when Neil Armstrong (1930-2012) became the first human to step onto the surface of the Moon during the Apollo 11 mission. Going further afield and establishing settlements beyond the asteroid belt requires identifying locations that are relatively stable and free of the enormous radiation fields associated with the giant gas planets.

In the Jovian system, Callisto has been suggested as a potential location for a station

The geological stability and relatively low radiation (compared to the other Jovian moons) has made Callisto a suggested target as a base and refuelling station for deep space missions to the outer Solar System (image: NASA). If we build a civilisation dispersed on a variety of planetary bodies, we may avoid extinction (unless /Solar System-wide catastrophe). Other branches would provide redundancy and robustness to the collapse (even if not extinction) of civilization in one location. If the presence in space becomes expansive enough and its economic scale sufficiently large, it might even be possible that space branches of humanity could help Earth civilization achieve a faster reconstruction if disaster befell it.

This is the concept of a multiplanet species

A civilization (represented as the black lines) located on one planet has a chance that a major catastrophe will destroy or cripple it (A). A civilization that has independent, self- sustaining branches in different parts of the Solar System (B) has a chance of surviving a catastrophe that destroys or temporarily incapacitates one of those branches. Will we become interstellar?

Human civilization became an interstellar spacefaring civilization in 2013.

The Voyager 1 spacecraft, launched in 1977, left the Solar System after exploring the giant gas planets of the Solar System.

Will humans follow it to other stars?

Metabolic diversity Geological Time The Hadean, Archean, Proterozoic and Phanerozoic are the four major eons.

Sometimes the Hadean, Archean and Proterozoic are lumped together in a supereon called the Precambrian / 88% of Earth’s history / biota exclusively microorganisms. Spiky distribution of molecules in biology vs. all kinds of molecules abiotic occurance

if spiky distribution detected -> interesting to search for life