Despite the multitudes of microbes that reside on earth, our knowledge of them is quite limited. Of the estimated nonillion (10³⁰) that exist, scientists have or are in the process of decoding 2,000 microbial genomes,  which means there is a vast unknown realm awaiting those researchers intent on exploring microorganisms that inhabit this planet.

In hopes of exploring that realm and expanding our understanding of microbes, a team from the the Department of Energy's Joint Genome Institute (DOE JGI) have released the first volume of the Genomic Encyclopedia of Bacteria and Archaea (GEBA), an analysis of the first 56 genomes representing two of the three domains of the tree of life. The encyclopedia is detailed in the December 24 issue of Nature.

Two days ago I offered you three problems in experimental particle physics, of varied complexity. Three readers tried answering the test in the comments thread: a rather underwhelming turnaround, but what did I expect - we are deep in Christmas vacations after all.

I will give below my own answers to the questions, and then comment some of those I received. For ease of reading, I paste here again the three questions.

Researchers at Columbia University's Mailman School of Public Health claim that children regularly exposed to tobacco smoke at home are more likely to develop early emphysema in adulthood. The findings, published in the December 2009 American Journal of Epidemiology, suggest that the lungs may not recover completely from the effects of early-life exposures to tobacco smoke (ETS), the research team says.

Cancer is commonly thought to progress by the growth of a primary tumor followed by metastasis, in which cancer cells leave the primary tumor and spread to distant organs. New research conducted by scientists at Memorial Sloan-Kettering Cancer Center shows, however, that circulating tumor cells can also return to and grow in their tumor of origin, a newly discovered process called 'self-seeding.'

The findings of the study, published in the December 25 issue of the journal Cell, suggest that self-seeding can enhance tumor growth through the release of signals that promote angiogenesis, invasion, and metastasis.

From the smallest South American monkeys to the largest African apes, the timing of molar development and eruption is closely attuned to many fundamental aspects of a primate's biology, according to Gary Schwartz, a researcher at the Institute of Human Origins and an associate professor in the School of Human Evolution and Social Change in ASU's College of Liberal Arts and Sciences.

With the first decade of the millennium coming to a close, it is time to take stock. What have 'The Noughties' brought us in terms of scientific advances?