Life in the Universe

Life in the Universe Phys178 2008week 12 part-2 Lecture 5 & 6: Life as we know it and Extreme Life A/Prof. Quentin A Parker PHYS178: Other worlds

Life as we know it Has changed a lot in 4 billion years! PHYS178: Other worlds

Life • Earth is a 'life planet'. • Probe anywhere on Earth and you will find life. • Organisms are everywhere on Earth: • Land, Sea and Air • The answer to what is life, however, is difficult. • We have examples of life but no clear definition… • Let’s have a chat about `life as we know it’. PHYS178: Other worlds

Carbon-Based Life • A complex life form such as a human, is assembled from a DNA genetic blueprint. • All life on Earth stores its genetic information in DNA or RNA which are carbon-chain molecules. • Carbon atoms can form long, complex, stable chains. • These chains are capable of extracting, storing, and using energy. PHYS178: Other worlds

Fossilized Bacteria • Here is an image of very old fossilized bacteria. • The artist's reconstruction shows its segmented structure. • This was found in 3.5 billion year old rock! • Life started early! PHYS178: Other worlds

Miller Experiment • Stanley Miller conducted an experiment in which he duplicated the early conditions on Earth. • He found, among other components, four amino acids. • Amino acids are the building blocks of life. • The atmospheric gases in his apparatus, when exposed to energy in the form of an electric arc, produced these compounds. PHYS178: Other worlds

Amino Acids-life’s building blocks Amino acids can link together to form long carbon chains. PHYS178: Other worlds

Protein-like Molecules • Here we see that single amino acids can be assembled into long protein-like molecules. • Also seen are microsphere forms with double layer membranes similar to cell walls. PHYS178: Other worlds

History of life on the Earth • Seen here is an entire history of the Earth. • The age of humans is the thin line on the top. • We are newcomers to the planet. PHYS178: Other worlds

Extreme life on earth • In the last few decades we have been discovering on earth more and more extreme environments in which life has been discovered • Environments in which the prospects of life had been considered highly unlikely • But the tenacity and diversity and ubiquity of earth-based life continues to amaze • The existence of life in even its most basic form in such harsh environments has changed our views on the prospects for extra terrestrial life PHYS178: Other worlds

In the complete blackness of deep ocean valleys • Life exists in abundance! • Tube-worms, mussells, crabs, shrimps and mircobes • No natural light • Extreme pressures • Extreme temperatures • Yet life is seen to flourish PHYS178: Other worlds

Tube-worms around `black-smokers’ PHYS178: Other worlds

Extreme life.. in ICE…… • Microbial cells have been found in ice cores from other locations on Earth. • The cores shown in this image were taken from above Antarctica's Lake Vostok and are being examined by researchers from the University of California at Berkeley and the University of Delaware. • Credit: University of Delaware PHYS178: Other worlds

ICE cores • Scientists with the Europa Focus Group collected this ice core from the North Slope of Alaska. • Studying unique microbes in ice will yield important clues about how organisms can live in bitterly cold environments on other planets. • Credit: M. Pruis PHYS178: Other worlds

Lake Vostok – a pristine environment • Lake Vostok is believed to contain water millions of years old, which may be the home of ancient organisms. • This hidden body of freshwater is the size of Lake Ontario and is the largest of 70 bodies of water first detected under the polar ice-sheet in the 1970s. • Credit: LDEO Columbia University PHYS178: Other worlds

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Lake Vostok • Lake Vostok is about the size of Lake Ontario, and researchers believe that it remains liquid thanks to a hydrothermal vent at the lake bottom. • Its waters are believed to harbour a low concentration of bacterial life, despite the fact that no sunlight has reached it for over a million years. • The meager ecosystem is probably nourished by hydrothermal energy from the floor of the lake. • The accreted ice offers an unusual opportunity for researchers to study these ancient life forms, because bacteria from many eras can be found, each trapped in its own layer and flanked by older and younger microbes that have been frozen in place throughout thousands of millennia. • The microbes are of particular interest to astrobiologists, who believe that extraterrestrial life may exist in similar locales – sequestered away from harsh surface environments, such as in Europa’s subsurface ocean. PHYS178: Other worlds

New earth `bug’ discovered deep underground… • A bug which lives entirely on its own and survives without oxygen in complete darkness underground has just been discovered in South Africa deep down in a gold mine. • Desulforudis audaxviator, or bold traveller as it is known in English, relies solely on water, hydrogen and sulphate for its energy – NO OXYGEN!!! • Because it survives without oxygen, it can perhaps offer clues to the possibilities of life on other planets. • This is the loneliest living species known to science • The rod-shaped bacterium was found 2.8km (1.74 miles) beneath the surface of the Earth in the Mponeng mine near Johannesburg, living in complete isolation, total darkness and 60C (140F) heat. PHYS178: Other worlds

Stromatolites • Life has been found in the most extreme conditions on Earth. • Stromatolites are some of the most ancient fossils found and yet still exist today. • These extremophiles can exist in environments in which 'normal' life would perish and are conditions which exist on several planets of the solar system. • On this basis simple life may be thriving elsewhere in our own solar system. • Q: Can you think ok any likely candidates? PHYS178: Other worlds

Viruses • Are viruses alive? • This has been a hotly debated topic for decades • Opinions differ on whether viruses are a form of life, or organic structures that interact with living organisms. • They have been described as "organisms at the edge of life”, since they resemble organisms in that they possess genes and evolve by natural selection and reproduce by creating multiple copies of themselves through self-assembly. • However, although they have genes, they do not have a cellular structure, which is often seen as the basic unit of life. • Additionally, viruses do not have their own metabolism, and require a host cell to make new products. They therefore cannot reproduce outside a host cell….. • but could viruses survive in space or be seeded from space? PHYS178: Other worlds

Carbonaceous Chondrites • Amino acids have been found in carbonaceous chondrite meteorites. • Amino acids and other complex molecules are apparently common in space…… • So the question is… can simple life be haboured by such things and can they be used to transport life around the cosmos? PHYS178: Other worlds

Some of the molecules that have been confirmed to exist in interstellar space Infrared spectroscopy in the 2.5-16 micron range is a principle means by which organic compounds can be detected and identified in space via their vibrational transitions. Ground-based, airborne, and spaceborne IR spectral studies have already demonstrated that a significant fraction of the carbon in the interstellar medium (ISM) resides in the form of complex organic molecular species.

Meteorite ALH84001 • Meteorite ALH 84001 seems to contain what is best described as fossilized bacteria. • In what environment did these organisms thrive? • There was further evidence that these organisms lived in the rock in which they died. • Materials which result from respiration were found around the fossils. PHYS178: Other worlds

Outline of what are believed to be possible microscopic fossils of bacteria-like organisms found in the meteorite ALH84001. PHYS178: Other worlds

Stars' Life Zones • A life zone around a star is a region where a planet could support life. • Of course, life is defined in our limited terms. • The sun's life zone is defined, as shown here, to include the space between Venus and Mars. • Note the change in the extent of thrse zones as a function of stellar spectral class (and hence temperature) PHYS178: Other worlds

Sensitivity versus range for radio signals PHYS178: Other worlds

Sensitivity vs range for SETI radio searches • The diagonal lines show transmitters of different effective powers. • The X axis is the sensitivity of the search. • The Y axis on the right is the range in light years, and on the left is the number of sun-like stars within this range. • The vertical line labeled SS is the typical sensitivity achieved by a full sky search. • The vertical line labeled TS is the typical sensitivity achieved by a targeted search such as from the Phoenix project (Source: NASA technical report CP-2156, 1979). PHYS178: Other worlds

Extrasterrestrial life • Extraterrestrial life is life originating outside of the Earth. • It is the subject of astrobiology, and its existence remains hypothetical until a concrete example can be shown. • There is no current really credible evidence of extraterrestrial life that has been widely accepted by the scientific community, • However, there are several hypotheses regarding the origin of extraterrestrial life if it exists. • One proposes that it may have emerged, independently, in different places in the universe. • An alternative hypothesis is panspermia, which holds that life emerging in one location then spreads between habitable planets. • These two hypotheses are not mutually exclusive. • The study and theorization of extraterrestrial life is known as astrobiology, exobiology or xenobiology. • Speculative forms of extraterrestrial life range from sapient or sentient beings to life at the scale of bacteria. PHYS178: Other worlds

Panspermia • One of the theories about how life on earth came in to being is the idea that living organisms are abundant in the cosmos and are transported to the earth by comets and meteorites. • Some evolutionists agree with this idea but they say that this only happened in the far past and that after that the development of life was very gradual. • However, even now life on earth can be influenced and changed by extraterrestrial life if we believe that extra-terrestrial bacteria and viruses still descend on earth on a regular basis. • This theory is called Panspermia. • It is clear all the basic building blocks are already out there in the COSMOS…. PHYS178: Other worlds

Radio Communication • The first step in communicating with intelligent life elsewhere is to find a common wavelength or radio channel. • This graph shows what is referred to as the 'water hole' wavelengths where at about 30 cm wavelength, communication would be relatively noise free. • Another civilization using similar technology to our radio technology, would know about this wavelength region. • To date, no signals have been found from extra terrestrial sources at these wavelengths. • It is pertinent to consider just how far our won signal will have reache dout into space… PHYS178: Other worlds

Arecibo Message • A message sent from the Arecibo radio telescope toward M13 is shown here. • To date, no artificial signals have been detected. • What are the chances of intelligent life existing elsewhere? PHYS178: Other worlds

The `WOW’ signal….. PHYS178: Other worlds

The WOW signal • The Wow! signal was a strong, narrowband radio signal detected by Dr. Jerry R. Ehman on August 15, 1977, • This was while working on a SETI project at the Big Ear radio telescope of the Ohio State University. • The signal bore some of the expected traits if it was of non-terrestrial and non-solar system origin. • It lasted for a mere 72 seconds, but has not been detected again. • It has been a focus for attention in the mainstream media when talking about SETI results. • Amazed at how closely the signal matched the expected signature of an interstellar signal in the antenna used, Ehman circled the signal on the computer printout and wrote the comment "Wow!" on its side. This comment became the name of the signal. • Source: Paraphrased text from Wikipedia PHYS178: Other worlds

The Galactic Habitable Zone • An annular region of our Galaxy in which it has been hypothesized that conditions are best suited to the development and survival of life as we know it. The GHZ was first proposed in 1991 by Guillermo Gonzalez of Iowa State University and Donald Brownlee and Peter Ward of Washington University, and has subsequently been endorsed by a number of other researchers, including Charles Lineweaver. Outside the galactic habitable zone (GHZ), the theory goes, various factors make the existence of complex (multicellular) life difficult if not impossible. The current GHZ is said to extend from 7 to 9 kiloparsecs (23,000 to 29,000 light-years) from the galactic center, is widening with time, and is composed of stars that formed between 4 and 8 billion years ago. The GHZ is analogous to the much more well established concept of the habitable zone of a star. PHYS178: Other worlds

According to the GHZ hypothesis, the width of the GHZ is controlled by two factors. The inner (closest to the center of the galaxy) limit is set by threats to complex life: nearby transient sources of ionizing radiation, including supernovae and gamma ray bursters, and comet impacts. Such threats tend to increase close to the galactic center. The outer limit is imposed by galactic chemical evolution, specifically the abundance of heavier elements, such as carbon. PHYS178: Other worlds

The Galactic Habitable zone Several key factors conspire to place our solar system in the so called habitable zone PHYS178: Other worlds

Factors in our immediate Galactic environment that may favour life The metallicity of our Sun appears to be just right to support terrestrial planet formation…. • Old stars located near the center region of our galaxy, are metal-poor because they formed • from just hydrogen, helium, and lithium. • Some of the the more massive stars complete their nuclear fusion cycles quickly and explode as supernovas. • The heavy elements produced from successive cycles of nuclear burning are dispersed into the interstellar medium. • Second generation stars are created out of these heavier elements, and each stellar explosion lead to a greater abundance of available metals. PHYS178: Other worlds

The importance of metallicity • A star of high metallicity, therefore, has material that originated from many previous generations of stars…. including all the heavy elements on earth that we believe a pre-requisites for life • Our sun has an unusually high metallicity compared to other solar-like stars, and the reason for this is not yet understood • whether this has an special bearing on the ability of earth to support life is unclear • It is possible that our star formed in a part of the Milky Way galaxy that had a high abundance of metals (elements heavier than helium), and then migrated to its present location. PHYS178: Other worlds

Planet formation • Recent statistical studies on the metallicities of stars with • extrasolar planetary candidates indicate that metal-rich • stars are more likely to have planets. • The most likely explanation is that a minimum threshold of metals is required to form rocky terrestrial planets and the cores of giant gaseous planets. • Therefore, a star that forms from an interstellar cloud high in heavy elements is more likely to form planets than a cloud deficient in metals. PHYS178: Other worlds

Avoiding the spiral arms… • Avoiding spiral arms, where new stars form, prevents our solar system from being gravitationally disrupted • Fortunately, our star orbits through the galaxy at nearly the same rate as the spiral-arm rotation • This synchronization protects our solar system from crossing a hazardous spiral arm too often • Avoiding spiral arms prevents our planet from encountering supernovae and giant molecular clouds, which can perturb the cometary bodies out of the Oort cloud leading to a higher number of cometary showers in the inner solar system which could lead to regular extinction level events. PHYS178: Other worlds

Much of our galaxy is a spinning disk. We create a unit, 1 "galactic orbit" = 250 Million years. Earth has circled the galaxy 18 times. The dinosaurs died out 2/5's of an orbit ago. Fish began almost 2 orbits ago. Multicellular life, about 4. Here are some comparisons orbits years 4 orbits ago 1 billion years  this is when multicelled life evolved 2 orbits ago 500 million years  Cambrian explosion 1 orbit 250 million years 3/4 orbit 188 million years 2/3 orbit 167 million years 1/2 orbit 125 million years 4/10 orbit 100 million years 1/3 orbit 83 million years 1/4 orbit 63 million years  dinosaurs on way out 1/5 orbit 50 million years 1/10 orbit 25 million years 4/100 orbit 10 million years 1/100 orbit 2.5 million years  humas begin to evolve 4/1000 orbit 1 million years PHYS178: Other worlds

Location of our Sun in the wider Galaxy.. Our solar system is located at a safe distance (about 8.5 kpc) from the Galactic Centre. This provides a safe haven from disruptive gravitational effects and harmful radiation produced from clouds of ionized gas rapidly moving around a supermassive black hole. If our solar system were located close to the Galactic Center, the combined perturbing effects from all the stars would cause a high flux of comets to rain in from the Oort comet cloud. The high number of cometary impacts would create regular global extinction events that would prevent complex life from evolving on the inner terrestrial planets over reasonable time-scales. PHYS178: Other worlds

The importance of radiation If our solar system were located near the inner region of the galaxy, the increased exposure to gamma radiation and x-rays, in addition to cosmic rays, would be lethal to any life trying to evolve on a terrestrial planet. The effects of radiation would damage the protective ozone layers of planets. In addition, secondary particle cascades created in the planet's atmosphere would be produced by high-energy particles. This would, in turn, increase radiation levels at the surface of the planet Life as we know it could not exists PHYS178: Other worlds

The Drake Equation… Is there extraterrestrial life (inc.intelligent life), on terrestrial planets around other stars? The first scientist to tackle this idea head on was Dr. Frank Drake via the famous equation: N = R* Fp Ne Fl Fi Fc Lwhere: N is the number of detectable technologically advanced civilizations in the galaxy R* the rate at which solar-type stars form in the galaxy. * Fp the fraction of solar-type stars that have planets. * Ne the number of planets per solar system suitable for life. * Fl the fraction of those Earth-like planets on which life exists. Fi the fraction of those life forms that are intelligent species. Fc the fraction of species that develop technology and choose to send messages L the lifetime of the technologically advanced civilization. The first 3 factors, R* Fp, & Ne can be estimated by direct observation. The first using statistical studies of star formation in the Galaxy from wide field surveys such as the AAO/UKST H-alpha survey. PHYS178: Other worlds

Life in the Universe