Life on Mars? How accumulated evidence slowly leads to scientific advances

Although the history of science is often presented as a series of eureka moments, with a single scientist's brainstorm paving the way for a paradigm-shifting theory, the truth is usually rather less dramatic. A good example of the latter is the formulation of plate tectonics, with the meteorologist Alfred Wegener's continental drift being rejected by the geological orthodoxy for over thirty years. It was only with the accumulation of data from late 1950's onward that the mobility of Earth's crust slowly gained acceptance, thanks to the multiple strands of new evidence that supported it.

One topic that looks likely to increase in popularity amongst both public and biologists is the search for life on Mars. Last month's announcement of a lake deep beneath the southern polar ice cap is the latest piece of observational data that Mars might still have environments suitable for microbial life. This is just the latest in an increasing body of evidence that conditions may be still be capable of supporting life, long after the planet's biota-friendly heyday. However, the data hasn't always been so positive, having fluctuated in both directions over the past century or so. So what is the correspondence between positive results and the levels of research for life on Mars?

The planet's polar ice caps were first discovered in the late Seventeenth Century, which combined with the Earth-like duration of the Martian day implied the planet might be fairly similar to our own. This was followed a century later by observation of what appeared to be seasonal changes to surface features, leading to the understandable conclusion of Mars as a temperate, hospitable world covered with vegetation. Then another century on, an early use of spectroscopy erroneously described abundant water on Mars; although the mistake was later corrected, the near contemporary reporting of non-existent Martian canals led to soaring public interest and intense speculation. The French astronomer Camille Flammarion helped popularise Mars as a potentially inhabited world, paving the way for H.G. Wells' War of the Worlds and Edgar Rice Burroughs' John Carter series.

As astronomical technology improved and the planet's true environment became known (low temperatures, thin atmosphere and no canals), Mars' popularity waned. By the time of Mariner 4's 1965 fly-by, the arid, cratered and radiation-smothered surface it revealed only served to reinforce the notion of a lifeless desert; the geologically inactive world was long past its prime and any life still existing there probably wouldn't be visible without a microscope.

Despite this disappointing turnabout, NASA somehow managed to gain the funding to incorporate four biological experiments on the two Viking landers that arrived on Mars in 1976. Three of the experiments gave negative results while the fourth was inconclusive, most researchers hypothesising a geochemical rather than biological explanation for the outcome. After a decade and a half of continuous missions to Mars, this lack of positive results - accompanied by experimental cost overruns - probably contributed to a sixteen-year hiatus (excluding two Soviet attempts at missions to the Martian moons). Clearly, Mars' geology by itself was not enough to excite the interplanetary probe funding czars.

In the meantime, it was some distinctly Earth-bound research that reignited interested in Mars as a plausible source of life. The 1996 report that Martian meteorite ALH84001 contained features resembling fossilised (if extremely small) bacteria gained worldwide attention, even though the eventual conclusion repudiated this. Analysis of three other meteorites originating from Mars showed that complex organic chemistry, lava flows and moving water were common features of the planet's past, although they offered no more than tantalising hints that microbial life may have flourished, possibly billions of years ago.

Back on Mars, NASA's 1997 Pathfinder lander delivered the Sojourner rover. Although it appeared to be little more than a very expensive toy, managing a total distance in its operational lifetime of just one hundred metres, the proof of concept led to much larger and more sophisticated vehicles culminating in today’s Curiosity rover.

The plethora of Mars missions over the past two decades has delivered immense amounts of data, including that the planet used to have near-ideal conditions for microbial life - and still has a few types of environment that may be able to support miniscule extremophiles.

Together with research undertaken in Earth-bound simulators, the numerous Mars projects of the Twenty-first Century have to date swung the pendulum back in favour of a Martian biota. Here are a few prominent examples:

• 2003 - atmospheric methane is discovered (the lack of active geology implying a biological rather than geochemical origin)
• 2005 - atmospheric formaldehyde is detected (it could be a by-product of methane oxidation)
• 2007 - silica-rich rocks, similar to hot springs, are found
• 2010 - giant sinkholes are found (suitable as radiation-proof habitats)
• 2011 - flowing brines and gypsum deposits discovered
• 2012 - lichen survived for a month in the Mars Simulation Laboratory
• 2013 - proof of ancient freshwater lakes and complex organic molecules, along with a long-lost magnetic field
• 2014 - large-scale seasonal variation in methane, greater than usual if of geochemical origin
• 2015 - Earth-based research successfully incubates methane-producing bacteria under Mars-like conditions
• 2018 - a 20 kilometre across brine lake is found under the southern polar ice sheet

Although these facts accumulate into an impressive package in favour of Martian microbes, they should probably be treated as independent points, not as one combined argument. For as well as finding factors supporting microbial life, other research has produced opposing ones. For example, last year NASA found that a solar storm had temporarily doubled surface radiation levels, meaning that even dormant microbes would have to live over seven metres down in order to survive. We should also bear in mind that for some of each orbit, Mars veers outside our solar system's Goldilocks Zone and as such any native life would have its work cut out for it at aphelion.

A fleet of orbiters, landers, rovers and even a robotic helicopter are planned for further exploration in the next decade, so clearly the search for life on Mars is still deemed a worthwhile effort. Indeed, five more missions are scheduled for the next three years alone. Whether any will provide definitive proof is the big question, but conversely, how much of the surface - and sub-surface - would need to be thoroughly searched before concluding that Mars has either never had microscopic life or that it has long since become extinct?

What is apparent from all this is that the quantity of Mars-based missions has fluctuated according to confidence in the hypothesis. In other words, the more that data supports the existence of suitable habitats for microbes, the greater the amount of research to find them. In a world of limited resources, even such profoundly interesting questions as extra-terrestrial life appear to gain funding based on the probability of near-future success. If the next generation of missions fails to find traces of even extinct life, my bet would be a rapid and severe curtailing of probes to the red planet.

There is a caricature of the stages that scientific hypotheses go through, which can ironically best be described using religious terminology: they start as heresy; proceed to acceptance; and are then carved into stone as orthodoxy. Of course, unlike with religions, the vast majority of practitioners accept the new working theory once the data has passed a certain probability threshold, even if it totally negates an earlier one. During the first stage - and as the evidence starts to be favourable - more researchers may join the bandwagon, hoping to be the first to achieve success.

In this particular case, the expense and sophistication of the technology prohibits entries from all except a few key players such as NASA and ESA. It might seem obvious that in expensive, high-tech fields, there has to be a correlation between hypothesis-supporting facts and the amount of research. But this suggests a stumbling block for out-of-the-box thinking, as revolutionary hypotheses fail to gain funding without at least some supporting evidence.

Therefore does the cutting-edge, at least in areas that require expensive experimental confirmation, start life as a chicken-and-egg situation? Until data providentially appears, is it often the case that the powers-that-be have little enticement for funding left-field projects? That certainly seems to have been true for meteorologist Alfred Wegener and his continental drift hypothesis, since it took several research streams to codify plate tectonics as the revolutionary solution. 

Back to Martian microbes. Having now read in greater depth about seasonal methane, it appears that the periodicity could be due to temperature-related atmospheric changes. This only leaves the scale of variation as support for a biological rather than geochemical origin. Having said that, the joint ESA/Roscosmos ExoMars Trace Gas Orbiter may find a definitive answer as to its source in the next year or so, although even a negative result is unlikely to close the matter for some time to come. Surely this has got to be one of the great what-ifs of our time? Happy hunting, Mars mission teams!

Biophilic cities: why green is the new black

I've previously discussed the notion that children who spend more time outside in natural surroundings are more likely to have improved mental and physical health compared to their indoors, gadget-centred peers, but does the same hold true for adults as well? After all, there have been many claims that the likes of the fractal geometry of natural objects, the sensual stimulation, the random behaviour of animals, even feeling breezes or better air quality can have a positive or 'wellness' (horrific term though it is) effect.

It is pretty much a given that the larger the percentage of nature existing within conurbations, the greater the improvement to the local environment. This begins at the practical level, with vegetation mitigating extremes of heat while its roots helps reduce flooding. In addition, fauna and flora gain more room to live in, with a greater number of species able to survive than just the usual urban adaptees such as rats and pigeons. What about the less tangible benefits to humans, culminating in a better quality of life? Science isn't wishful thinking, so what about the evidence for more nature-filled urban environments improving life for all its citizens, not just children?

Studies suggest that having window views of trees can increase concentration and wellbeing in the workplace, while for hospital patients there is a clear correlation between types of view and both the length of recovery periods and painkiller usage. Therefore it seems that even the appearance of close-at-hand nature can have an effect, without the necessity of immersion. Having said that, there are clear advantages to having a public green space, since it allows a wide range of activities such as flying kites, playing ball games, jogging and boot camps, or just having a picnic.

Our largely sedentary, over-caloried lives necessitate as much physical activity as we can get, but there is apparently something greater than just physical exercise behind nature as a promoter of wellbeing. Investigation appears to show that spaces with trees and the hint of wilderness are far more beneficial than the unnatural and restricted geometries of manicured lawns and neatly maintained flower beds. It seems that we are still very much beholden to the call of the wild. If this is a fundamental component of our highly civilised lives, are urban planners aware of this and do they incorporate such elements into our artificial environments?

The concept of integrating nature into our towns and cities certainly isn't a new one. As a child, I occasionally visited Letchworth Garden City, a town just north of London. As the name suggests, it was an early form of 'Green Belt' planning, created at the start of the Twentieth century and divided into sectors for residential, industrial and agricultural usage. In its first half century it tried to live up to its intention to be self-sufficient in food, water and power generation, but this later proved impractical. I don't recall it being anything special, but then its heyday as a mecca for the health conscious (at a time when the likes of exercise and vegetarianism were associated with far left-wing politics) has long since passed. As to whether the inhabitants have ever been mentally - or even physically - advantaged compared to the older conurbations elsewhere in the UK, I cannot find any evidence.

Across the Atlantic, the great American architect Frank Lloyd-Wright conceived of something similar but on a far larger scale. His Broadacre City concept was first published in 1932, with the key idea that every family would live on an acre-sized plot. However, Lloyd-Wright's concept - apart from being economically prohibitive - relied on private cars (later updated to aerator, a form of personal helicopter) for most transportation; sidewalks were largely absent from his drawings and models. Incidentally, some US cities today have partially adopted the sidewalk-free model but without Lloyd-Wright's green-oriented features. For example, there are suburbs in oil-centric Houston that are only reachable by car; you have to drive even to reach shopping malls you can see from your own home, with high pedestrian mortality rates proving the dangers of attempting to walk anywhere. Back to Lloyd-Wright: like many of his schemes, his own predilections and aesthetic sensibilities seem to have influenced his design rather more than any evidence-based insight into social engineering.

In recent years the term 'biophilic cities' has been used to describe conurbations attempting to increase their ratio of nature to artifice, often due to a combination of public campaigning and far-sighted local governments. Although these schemes cover much wider ground than just human wellbeing (prominent issues being reduction in power usage and waste, greater recycling and ecological diversity, etc), one of the side effects of the improvements is to quality of life. Thirteen cities joined the Biophilic Cities project in 2013, but others are just as committed in the long-term to offsetting the downsides of urban living. Here are three cities I have visited that are dedicated to improving their environment:

1. Singapore. Despite the abundance of tower blocks, especially in its southern half, this city that is also a nation has a half-century history of planting vegetation in order to live up to the motto ‘Singapore - City in a Garden’. Despite its large-scale adoption of high-tech, high-rise architecture, Singapore has preserved an equivalent area of green space and now ranks top of the Green View Index. Even the maximal artificiality of the main highways is tempered by continuous rows of tall, closedly-packed trees while building regulations dictate replacement of ground-level vegetation lost to development. A new 280-metre tall office, retail and residential building, due for completion in 2021, is set to incorporate overtly green elements such as a rainforest plaza. It could be argued that it's easy for Singapore to undertake such green initiatives considering that much of city didn't exist before the late Twentieth century and what did has been subject to wide-scale demolition. However, it seems that Singapore's Government has a long-term strategy to incorporate nature into the city, with the resulting improvements in the mental and physical wellbeing of its inhabitants.
2. Toronto. Although not as ecologically renowned as Vancouver, the local government and University of Toronto are engaged in a comprehensive series of plans to improve the quality of life for both humans and the rest of nature. From the green roof bylaw and eco-friendly building subsidies to Live Green Toronto Program, there is a set of strategies to aid the local environment and planet in general. It is already paying dividends in a large reduction of air pollution-related medical cases, while quality of life improvements are shown by the substantial bicycle-biased infrastructure and increase in safe swimming days. There's still plenty to do in order to achieve their long term goals, particularly around traffic-related issues, but the city and its inhabitants are clearly aiming high.
3. Wellington. New Zealand's capital has wooded parks and tree-filled valleys that the council promotes as part of the city's quality of life. The recreated wetlands at Waitangi Park and the Zealandia (formerly Karori) predator-proof wildlife sanctuary are key components in the integration of large-scale nature into the urban environment. Indeed, the latter is proving so successful that rare native birds such as the kaka are being increasingly found in neighbourhood gardens. Both the city and regional councils are committed to improving both the quality of life for citizens as well as for the environment in general, from storm water filtering in Waitangi Park to the wind turbines on the hilltops of what may be the world's windiest city.

These cities are just the tip of the iceberg when it comes to conurbations around the world seeking to make amends for the appalling environmental and psychological consequences of cramming immense numbers of humans into a small region that cannot possibly supply all their needs. In some respects these biophilic cities appear too good to be true, as their schemes reduce pollution and greenhouse gas emissions, improve the local ecosystem, and at the same time appear to aid the physical and mental wellbeing of their inhabitants. Yet it shouldn't be surprising really; cities are a recent invention and before that a nomadic lifestyle embedded us in landscapes that were mostly devoid of human intervention. If we are to achieve any sort of comfortable equilibrium in these hectic times, then surely covering bare concrete with greenery is the key? You don't have to be a hippy tree hugger to appreciate what nature can bring to our lives.