This week in the Planet Earth Podcast - how hikers and walkers could be unwittingly changing the landscape by spreading alien species; what it's like to work as a marine biologist in the Arctic in temperatures of minus 40°C; and exactly how stable is the West Antarctic Ice Sheet?

• Spreading aliens, Arctic experience, and Antarctica - Naked Scientists Science Podcasts and Science Radio Shows
• Life Where the Sun Don't Shine... - Podcasts
• Alien Hikers - Planet Earth Online - Interviews
• Planet Earth Online - Bryozoans and Antarctic History - Interviews
• SETI, Aliens and the Origins of Life - Podcasts
• Checking the Atmosphere and Changing the Climate - Podcasts