A fantastic question! It's not just stem cells you need to consider, but indeed any type of organ transplant or tissue donation. Another person, unless they are your identical twin, will have DNA different from your own. The reason lung transplants or bone marrow transplants actually work is because you are substituting dodgy tissue for healthy tissue. At the same time, you are replacing a gene that has gone wrong by putting in a healthy copy of the gene. That means the DNA in the tissue you've replaced will be different. The rest of your body won't change. If you do a bone marrow stem cell transplant for someone with leukaemia, the cells that you will have inside your bone marrow will come from your donor. Therefore, they will also be genetically identical to the donor. This means that a man who receives a bone marrow transplant from a lady will have bone marrow cells that have two X chromosomes. Sometimes people can even see a change in their blood group.

Lake Vostok is a very large lake underneath the main 2km-thick ice sheet of eastern Antarctica and has been isolated from surface for a half a million years. There has been a project to drill through the ice sheet down to Lake Vostok that's been running for quite a few years. They started drilling and got to about 50 metres above the lake itself and decided to stop. They weren't sure if there would be any life in the lake, and there was also the problem of infecting the lake with modern microbial material. It could therefore contaminate an undisturbed environment. People have been trying to invent a sterile drill to get around these problems. I don't know the exact date of going into the Lake.

Like everything else, it's really difficult to convince people that things are really happening. There's also the problem of making the economics of these large issues aware to the public and convincing them that we need to take action. Just as we took action over CFCs and the ozone hole, we now need to address the issues regarding elevated CO2.

They probably didn't have a great direct effect on our climate. Such explosions are actually small in comparison to something such as a volcanic eruption, which releases so much debris that they end in global cooling rather than global warming. What the explosions have done is provided a radioactive marker in the land and in plants.