The paper reads as more conjecture than fact. There are a few interesting threads that they are pulling on, but they seem to make a giant leap that

1. There is well established evidence of extraterrestrial microbes in meteorites

2. Earth is constantly bombarded with life bearing rocks, to the point that it is likely that “red rain” is non terrestrial.

3. Evolution events such as the octopus evolving from squid are from injection of genes by extraterrestrial retroviruses

I stopped reading at this point as the conjecture didn’t seem to lead to something substantive. If 1 and 2 are true we should have immediate access to an entire interstellar ecosystem. The space of possible mechanisms for abiogenesis grows exponentially. A distinct set of questions arise like does evolution occur in in asteroids? Do ecosystems on isolated rocks interact every few million years? Are the rocks coming into contact with earth from other life bearing worlds?

The paper answers none of these questions and doesn’t seem to grasp the implications it’s laying out.