EXKN stands for Explanatory Knowledge.  As far as we know, humans are the only source of this type of knowledge in the universe.  This knowledge is born of our unique creative abilities and can be used to solve the unending stream of problems that always face us.  
 
To understand why humans are cosmically significant in this way, requires a deeply rational conception of our world.  The philosophical and scientific underpinnings of this conception were inspired by Karl Popper, and further developed by David Deutsch in his two books, The Fabric of Reality (1998) and The Beginning of Infinity (2011).

David is a theoretical physicist who is well known for his pioneering work in the field of quantum computation, but he is also a broad philosophical thinker who has developed a deeply unified view of our world that brings together four fundamental theories that have traditionally been considered separately.   These are not new theories, but rather the best explanations of our reality that we have.  They include the Theories of Quantum Physics, Evolution, Computation and Knowledge.

Quantum physics and the theory of relativity are the deepest and most successful theories of physics and they contain the higher order laws of nature that are known to hold true everywhere in our universe.

The best we can do to make sense of our reality is to conjecture good explanations for the phenomena around us, and further refine or abandon them through criticism.  This is how humans create explanatory knowledge which is objectively different from the evolutionary knowledge contained in our genes.  This creative ability allows humans to be universal constructors, capable of causing any physically possible transformation of raw materials, once they know how.

For this to be possible, the universe must be comprehensible and computable.  The theory of computation shows that this is indeed the case, and that a "universal computing device can simulate every physical process".  This allows for the knowledge we generate to have universal reach and application.  It can cause jumps to universality in technologies and change the course of history in ways that could not be predicted by theories of physics alone.

Artificial general intelligence (AGI) sits on our horizon as this ever approaching specter, evoking disbelief, fear, and pessimism.  The theory of computation implies that AGI must be possible, and the fact that evolution was able to create AGI (us), also implies that we will eventually be able to figure it out as well.   When we do we will also have to grow our moral knowledge to navigate all the implications.   Since we don't fully understand the source of our own creativity yet, it is unlikely that current AI efforts are on the correct path.  

The theory of computation also explains how channels of information flow through our world.   These processes transcend material substances and can transition abstract ideas from one physical instantiation, such as a brain, to another.   Such information can also be thought of as memes, which are ideas that replicate.  The most successful memes are good at getting themselves replicated but they can often be irrational.   Memes can have deep cultural implications as societies that become dominated by anti-rational memes tend to be static and make little progress.

Most of human history has been characterized by static societies where progress has been almost non-existent or very slow.  It wasn't until the recent Enlightenment period that an openness to new ideas and rational criticism of them developed.  Since then we have seen rapid progress in the growth of scientific and moral knowledge, especially in dynamic Western societies that are increasingly influenced by rational memes.  Dynamic societies have the potential to continuously improve while remaining stable, if they adopt systems that allow them to make good choices and error correct them peacefully and quickly whenever their choices aren't working out.

Humans have always faced problems.  On our journey from our prehistoric origins on the African savannah, we have slowly accelerated our ability to solve the problems we faced by creating the knowledge to overcome them.  Problems present the opportunity for further knowledge creation, but they never end, as all solutions to problems just lead to new questions or problems.  If the proposed solution to a problem does not break any law of nature or physics then it is just a matter of finding the right knowledge to make it possible.

This ties into David Deutsch's unique view on optimism, which is that "all evils are caused by an insufficient amount of knowledge".  Optimism is a requirement for sustaining progress.  This is not to say that continual unbounded progress is inevitable, just that it is actually possible.

The growth of knowledge is inherently unpredictable but can lead to progress in all domains from scientific to moral.  Supporting the ideas that allow dynamic societies to thrive and prosper gives us a chance at infinite progress.