WIDE ANGLE
Panspermia: How did life come to Earth?
'The seeds of life called shotgun on a rocky-ride to the planet Earth is a statement re-imagined from the theory of Panspermia, discussed by Svante Arrhenius, in his book "Worlds in the Making" back in the early 1900s. The concept has three parts, i) The ejection of the seeds on its vehicle, ii)Their journey through space, iii)Their landing on Earth. Through time the theory has evolved from the concept of Lithopanspermia to Massapanspermia i.e the seeds of life are now believed to have been so non-fastidious, to have primarily relied on their mass (and not just rock) to protect them during their journey through space.
To investigate this theory, Akihiko Yamagishi's group assayed the survival of an extremophilic species Dienococcus radiodurans in space on a mission called Tanpopo(the Japanese word for dandelion, befitting the objective of the mission) over a period of 3 years while looking at the parameters affecting their survival, like temperature, humidity, exposure to UV and ionizing radiation. Their hypothesis was to corroborate the theory of massapanspermia, which translates to the ability of the species to survive in space on the basis of the thickness of their cell aggregate. To test this they exposed cultures of varying thickness in special aluminium plates prepared for space travel to the International Space station where they were exposed to space for a time period of 1-3 years, with controls inside the space station. Since UV radiation is known to cause DNA damage, one of their primary objectives was to assay the DNA damage caused and the mechanism of DNA damage as they wished to explore what made the D. radiodurans survive the dangers of space. Their results show a higher ability of double-stranded break repair by the species and a possible shielding effect from UV, provided the layer of dead cells on the outermost surface of the cell aggregates. They estimate that the shortest travel time for a meteoroid to travel from Mars to Earth could be a few months to years, however, the frequency is very low. In conclusion, they've provided evidence for the plausibility of the seed's journey through space while, work on the 'ejection from host planet' and 'landing on earth' of the seeds is yet to be studied.
References:
1.Yuko Kawaguchi , Mio Shibuya , Iori Kinoshita , Jun Yatabe , Issay Narumi , Hiromi Shibata , Risako Hayashi , Daisuke Fujiwara , Yuka Murano , Hirofumi Hashimoto , Eiichi Imai , Satoshi Kodaira , Yukio Uchihori , Kazumichi Nakagawa , Hajime Mita , Shin-ichi Yokobori and Akihiko Yamagishi.Frontiers in Microbiology. Aug 2020.https://www.frontiersin.org/article/10.3389/fmicb.2020.02050
2.Akihiko Yamagishi, Yuko Kawaguchi, Hirofumi Hashimoto, Hajime Yano, Eiichi Imai, Satoshi Kodaira, Yukio Uchihori, and Kazumichi Nakagawa.Astrobiology.Nov 2018.1369-1374.http://doi.org/10.1089/ast.2017.1751