Synthetic biologists may use computers to design gene sequences that don't exist in nature, have those sequences chemically synthesized, and then insert them into the genome of existing organisms. (montereyherald.com)
A more moderate argument is that, while highly unlikely, there is a chance Martian microbes could have a harmful impact on Earth, by competing with existing organisms for example. (science.howstuffworks.com)
However, only with the recent advent of extensive genomic sequencing has molecular biology been able to look backward in time in the same way, using the record of events preserved within the genomes of existing organisms. (complex-life.org)