Sam, Hitchin asked:
Is the Earth getting heavier owing to plant photosynthesis converting energy into mass. And if so, does this affect the Earthís spin?
We have actually looked at this in the past and the answer is actually, yes. Because E=mc2, Einsteinís famous equation, (E) energy equals (m) mass, times (c), the speed of light squared. So, if you increase the energy in the system then the mass must also increase. The Sun is adding energy to the Earthís system in the form of chemical energy; this arrives as light and is converted into chemical energy by photosynthesis. Therefore, the Earth is gaining a little bit of weight in the form of the entrapment of that energy within plant chemistry. But, compared with the 40,000 tons of dust and material that rains in on Earth from space every year, itís quite literally a drop in the ocean. So, on the whole, the Earth is gaining a bit of weight as plants in the biosphere capture energy coming from the Sun.