On Theories

‘Theory’ is a word that is often bounded around in the media and politics. It is also very extensively used in the sciences. However, it is here that it often takes on a different meaning to that which the public assume, a meaning that does not accurately convey the scientific process.

Science is comprised of very little fact and very, very many theories, also known as hypotheses. To be frank, any scientist that presents their work as fact should be discredited immediately and hang their head in shame. Each scientifically accepted theory, or hypothesis, is merely the best estimation available to describe or explain the relevant observation(s). It is an idea that has survived the rigours of peer-review and repeated and independent verification to become accepted as the best explanation available to account for the observed results. Even at this point however, it is not fact. Far from it. New information, analysis or technology may in the future, near or distant, prove it wrong despite years, decades or even centuries of obedient acceptance, and a new theory will have to be devised, tested and retested to take its predecessor’s place. This is how science is done, how it progresses and moves forwards. The ephemeral nature of the process, from inception to acceptance, is perhaps what sets science apart from other disciplines. No theory is sacred; they can all be revolutionised in an instant.

This definition extends to include popular and extensively researched hypotheses, such as the theory of evolution by natural selection and Einstein’s theory of relativity – itself a product of revolutionising Newton’s earlier theory of gravitation that had been accepted for over 300 years. These are the best, the most rigorously tested and repeatedly challenged theories to survive the scientific process and become accepted as the nearest available approximation to describe the speciation of  living creatures and the physical laws governing the movement of large planetary bodies, respectively. They are great examples of theories that have stood the test of time: evolution by natural selection first being proposed by biologists Charles Darwin and Alfred Russel Wallace in the mid to late 19th century.

As a great example of the misapprehension of the meaning of theory in the scientific sense, evolution as a ‘theory’ is one of the favourite jumping-off points for religious creationists who point to the perceived uncertainty inferred by the word as an effective argument against its ability to accurately describe the fundamental driving force behind biology. “Ah, but it’s only a theory”, they say, “and therefore it is merely your opinion that it is more effective at describing speciation than the Genesis saga of the Old Testament”.  This viewpoint illustrates two things. Firstly, a fundamental misunderstanding of the term ‘theory’ as a descriptor of a scientific paradigm, and secondly, a basic understanding of biology.

An example of a testable theory (from the wonderful webcomic xkcd)

Just because it is ‘only’ a theory doesn’t mean it can be completely discredited in one fell-swoop. Extraordinary claims require extraordinary evidence, and paradigm-changing ideas are only very rarely accepted as theory without serious opposition and incredible evidence. Generally, it is a gradual process – improvement, tinkering, refining, acceptance. If creationist ideas had anywhere remotely near as much scientifically verified evidence in support as evolution does, it would have to be accepted by science. The process is not defined by the religious ideas or politics of individual scientists, despite the insistence of certain areas of the media, but rather by whichever theory has the greater corroborating evidence behind it. If it was the case that it was creationism or intelligent design or aliens that were responsible for differentiating all life on Earth, and the evidence was robust, scientists would be in support. But the fact, and this is a fact, is that it simply isn’t.

The Great Revolution

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Around 2.3 billion years ago our planet underwent what was perhaps the most significant and dramatic revolution in its history. However, this was not a revolution that we may be familiar with. There was no political basis to this transition, perhaps involving a suppressed population rising up in unison against a brutal dictator. This was a revolution was on a truly global scale and it was instigated by the chemistry of the planet. In this case, and quite literally, change was in the air.

During much of the Archean eon, between 3.9 and 2.5 billion years ago, the composition of the atmosphere of the Earth was dominated, as it is today, by nitrogen, but also by gases such as methane and hydrogen sulphide. These gases are ‘reducers’ (as opposed to ‘oxidisers’) that ‘donate’ one of their electrons to another substance in reaction. Oxygen, an oxidant, was a minor constituent, representing less than one part per million (1 ppm) of the atmosphere. About 2.3 billion years ago however, this all changed. This momentous and eon-defining event is known as the Great Oxidation to earth scientists, and it represents a truly life-changing transition in the history of the planet. Oxygen concentrations jumped (in relative terms) to between 1 and 10% of the present atmospheric level (PAL for short).

Cyanobacteria – the agents of change (Michael Abbey – Science Photo Library)

The puzzling thing however, is that oxygenic photosynthesis (OP) had already been active in primitive cyanobacteria (similar to the one above) for at least 300 million years before the Great Oxidation, originating sometime between 3.2 billion and 2.6 billion years ago, with the most convincing evidence placing its genesis at 2.7 billion years before present. Organisms had evolved the extraordinary ability to use photons of light to split water molecules and combine them with carbon dioxide to form complex sugars, in the process releasing oxygen gas as a by product.  The evolution of oxygenic photosynthesis was in itself an incredible feat, involving some of the most complex cellular biomachinary ever discovered.  Why, then, was the atmosphere of the early Proterozoic eon so oxygen-poor?

The answer, it turns out, is a rather complicated one. Oxygen concentrations during the transitional period before the Great Oxidation, but after the evolution of OP, were spatially variable, concentrated around the organisms responsible for its production as a waste gas. Any oxygen that made it into the air was quickly destroyed by reaction with methane against the backdrop of a highly (ultraviolet – UV) irradiated atmosphere. The reductant-dominated atmosphere was a product of volcanic out-gassing which provided a constant source of reduced gases such as hydrogen, hydrogen sulphide, methane and carbon dioxide. Any oxygen that wasn’t destroyed by reaction with these gases was mopped up by the large swathes of reduced material likely to be present on the surface of the Earth – including iron and iron pyrite (which was transformed from its reduced ferrous state to its oxidised ferric form) and resulting in the iconic banded iron formations (or BIFs) associated with this time. It would appear that oxygen could not maintain a foothold in this reducing world, struggling to maintain a low concentration which would have been spatially patchy and probably variable in time as well. Its sources were balanced by its sinks, as the chemists say.

In order to come to dominate, something would have to break the cycle – an imbalance between the sources of oxygen (i.e. the oxygenic photosynthesisers) and its sinks (methane photolysis and reaction with reduced gases and material from the mantle). Luckily for us as oxygen dependent organisms, something did break the feedback loop and that something was the humble hydrogen molecule.

Hydrogen in its elemental or ‘free’ variety is a reductant, reacting excitedly with oxygen to form water vapour, but in the upper atmosphere it behaves rather differently. At the base of the atmospheric homopause, around an altitude of ~ 100 km, water vapour is absent – frozen out at the stratospheric ‘cold trap’ at 20 km, but hydrogen molecules can be found hitching a lift within the structure of the methane molecule (CH4) which is light enough to rise through the homopause.  The methane molecule  is attacked by the UV-generated radicals in the upper atmosphere (O, OH) and yields hydrogen atoms that can diffuse right to the very top of the planetary atmosphere, known as the exobase, at around ~ 500 km. Here, some of the light hydrogen atoms – the high energy tail of the distribution – are accelerated to a velocity that allows them to overcome the gravity of the Earth and permanently escape into space. This mechanism, over millions of years, resulted in a net increase in oxygen by the erosion of a finite hydrogen (reductant) reservoir, pushing the balance of sinks and sources of oxygen to the side of the sources. This process is still occurring on the Earth, but at a much lesser rate than in the past due to the fact that methane is now less abundant than it once was.

At a critical point, estimated to be around 1 ppm by volume of oxygen, an ozone layer began to form in the stratosphere. This layer served to shield the Earth below from UV light and thereby prevented the reaction of methane and oxygen in the lower atmosphere, shifting the balance in the favour of oxygen once again and increasing its concentration further still.

The age of oxygen had dawned.

Perhaps I disposed of the political revolution analogy too soon. Let us think of oxygen gas as a suppressed minority but with the great potential to usher in a new age of organism diversity and to completely revolutionise the Earth system. Methane & co. form the oligarchy of the reductants, dominating the atmosphere and violently reacting with any oxidants they encounter (using their oppressive, ruthless army of UV light) to prevent an oxidising majority from forming. They insist upon the use of traditional, inefficient metabolic pathways such as hydrogen sulphide fermentation to power the small, putative organisms over which they rule. But the agents of change, the oxygenic photosynthesisers, are working studiously to infiltrate the atmosphere and gradually, with the protection provided by the revolutionary guard molecule, ozone, they eventually overthrow the reductants, banishing them to the depths of the oceans, lakes or the guts of cows and ushering in a new age of glorious oxygen domination!

Of course, this is just a metaphor and not a particularly good one at that. The real revolution took hundreds of millions of years and firmly without the inferred teleology or determinism that stems from my anthropic bias. Oxygen is a poison, and to the majority of life on the early-Earth, the dawn of the Great Oxidation marked the end of their reign as surface dwelling organisms. However, without it complex organisms would not have evolved. Anaerobic respiration is several orders of magnitude less efficient and therefore unsuitable for powering large, complex bodies that require more energy – energy that can only be provided by an oxygen metabolism.


Much of the information and insight for this post comes from Tim Lenton and Andrew Watson‘s excellent book, Revolutions that Made the Earth, which was published last year. It is available on Amazon.

Interview with Brian Shiro (CEO of Astronauts4Hire)

Brian Shiro is the Chief Executive Officer of Astronauts4Hire

In this post I have the pleasure of letting someone else do the writing for a change. That person is Brian Shiro and he is the Chief Executive Officer of Astronauts4Hire (A4H). Their official press release footer reads as follows:
Astronauts for Hire, Inc. (A4H) is a  501(c)(3) non-profit corporation whose objectives are to provide opportunities for students and professionals to develop and refine the skills necessary to become commercial astronauts and to assist these qualified candidates with networking opportunities in the space research community. A4H’s commercial astronaut candidates are accomplished scientists and engineers who can support a wide variety of payloads. They are available today for contract and consulting work with researchers to design and conduct experiments on microgravity, suborbital, and orbital missions.
Brian kindly agreed to answer some questions about what it is A4H does, and what his plans are for the future of the company.
1. Do you agree that commercial space companies like Astronauts4Hire are the future of suborbital space transportation and research?
Brian Shiro: I think that the suborbital spaceflight industry will be dominated by commercial companies operating spacecraft for a variety of clients, both private and public.  While tourism is driving much of this development so far, there is only a finite number of people wealthy enough to afford a 5-minute joyride in space.  Once that population of clients has run its course, what will sustain the suborbital spaceflight industry?  Either prices must fall dramatically, or another type of client needs to emerge.  I think researchers are that other type of customer.  Unlike tourists who may only go on one flight, scientists can repeatedly apply for research funding from agencies like the NSF, NASA, or NIH to have their experiments fly in space.  Tourism will never go away, but I think research will eventually dominate the landscape of suborbital flights.  Consider the analogy of Antarctica.  Like space, it is a harsh, remote environment that is expensive to reach.  While some tourists do indeed venture there at great personal expense, almost everyone who goes to Antarctica is a scientist or supports the science activities in some way, I believe that is the fate of the suborbital realm in the foreseeable future.
2. What projects are Astronauts4Hire currently involved in?
Brian: Our most important focus is on building the organization.  At almost 1.5 years old, we are still very young and are evolving rapidly.  Fortunately, we are out front leading the way as this new frontier emerges.  To prepare our members for the rigors of spaceflight and the demands of doing research there, we have developed a comprehensive medical and training qualification program in consultation with expert advisors.  We’re currently working on getting this published so it can get input from the wider community.  Another project has been helping the Commercial Spaceflight Federation recruit Research & Education Affiliate members, which is the status A4H holds in that organization as well.  In collaboration with some of our training and research partners we are working on joint projects ranging from human physiology to developing high fidelity astronaut training courses.  Look for exciting announcements about those projects in the coming months.
3. What are your plans for the future development of Astronauts4Hire?
Brian: Five years from now, I expect A4H to be well established as an authority setting commercial astronaut training standards and as a primary resource to the research community to reliably fly its experiments in space and/or test them on parabolic flights.  Hopefully, we will have already completed at least one actual suborbital spaceflight by that point.  By ten years, A4H should be regularly operating both suborbital and orbital research missions.  In the decade that follows I expect the demand for non-research astronauts to grow to include other “blue collar” support roles to help maintain and operate private space stations, for example.  A4H is positioning itself to serve all of these markets as an astronaut crew service.  Right now, we’re a volunteer-based organization relying upon virtual collaboration tools, but I would expect us to eventually establish a physical office, full-time staff, and perhaps even our own training facilities to help facilitate our activities.
4. Who can become an Astronaut4Hire?
Brian: Anyone can join the organization as an Associate Member.  As an Associate Member you can optionally get involved with A4H projects to support the organization and train to meet your astronaut goals.  Currently, there are 46 Associate Members in A4H.  The other type of members are Flight Members.  These are the “astronauts for hire” of the organization.  Selection as a Flight Member occurs on a competitive basis about once per year.  There are currently 22 Flight Members.  It is necessary to keep this group relatively small to maintain a high degree of quality control on our “product”, meaning the astronauts we can offer to clients.  Also, we don’t have infinite resources to support the training needs of an unlimited number of people, so we have to keep the Flight Member group selective.  The main difference between Associate and Flight members is that Flight Members have access to training scholarships to help offset the cost of astronaut training and can represent A4H as “astronauts for hire” on research contracts with clients.  Generally speaking, to be competitive as a Flight Member, we’re looking for well established scientists or engineers with a broad background indicating adaptability.  Experience in risky operational environments like piloting aircraft, SCUBA diving, mountaineering, etc. are also important indicators that applicants can think clearly under stress.
5. What training do you provide for your astronauts?
Brian: Our training philosophy is that A4H astronauts should be as prepared as possible for whatever situation they might face.  Unlike spaceflight participants who may only fly in space once and therefore only need minimal training, A4H crew astronauts plan to fly many times over the course of a career.  This multiplies the chances for off-nominal events from occurring.  Thus, our training includes preparing for both the planned mission elements and the unplanned emergency situations.  First is academic training, which includes earning at least a Master’s degree in a technical field and completing short courses on spaceflight, the space environment, and human factors.  The astronaut training includes the following major elements: high-G training in a centrifuge, high-altitude hypoxia training in an altitude chamber, microgravity training on parabolic flights, distraction training, emergency egress training, unusual attitude training in acrobatic aircraft, SCUBA diving, private pilot, and survival.  We have organized these into two qualifications we are calling “Research Specialist” and “Operations Specialist”, which are roughly analogous to NASA’s payload and mission specialists, respectively.  Look for a paper from us on this subject in an upcoming peer-reviewed journal by early next year.
6. How can the public get involved?
Brian: One of our important goals of A4H is to excite and inspire the public about the new era of commercial spaceflight.  Members of the public are encouraged to contribute donations, sign up to receive A4H’s quarterly newsletter, or join as Associate Members.  We are happy to come speak to schools or other events anytime too.
7. Do you foresee any conflicts-of-interest between private sponsors and future space missions?
Brian: One can imagine scenarios where sponsors could try to abuse their influence as major financial contributors to the A4H organization.  For example, it would be a conflict of interest for a donor to expect favoritism in an A4H Flight Member or scholarship selection.  Perhaps more insidious would be the notion that an entity hiring A4H for a job could ask A4H to do something to endanger the flight or people on the ground.  Obviously, we would refuse any such requests.  It is critical that all A4H members conduct themselves with the highest ethical conduct, and the missions we perform for clients must also adhere to strict safety standards.  As a 501(c)(3) nonprofit, A4H must primary serve the public interest as it builds the next generation of astronauts in the post-Shuttle era of commercial spaceflight.
8. What advice would you give to someone hoping to become an Astronaut4Hire?
Brian: If we’re right, research applications are what will drive the demand for private spaceflights in the foreseeable future.  Therefore, you must either be an accomplished researcher yourself or be very comfortable working with researchers.  Having an advanced postgraduate degree (Master’s, Ph.D.) in a field of science or engineering will be required to have the necessary background to work in this new industry.  Having experience in a broad set of fields will help you be competitive to operate a wider variety of payloads/experiments.  Earning your private pilot’s license, SCUBA certification, and other similar high-demand pursuits will give you experience working in stressful environments which require strict adherence to procedures in order to remain safe and survive.  Last, but not least, experience in the business and/or nonprofit sector(s) is highly valuable.  We need people with fundraising, marketing, and organizational skills to make A4H work.
Brian answers more questions about Astronauts4Hire in this interview on the Space Business Blog. He is also on Twitter, you can follow him here. You can also follow his personal blog, astronaut for hire.