There's a ton of bollocks in the article...
Thanks, Palf. Your comment puts things in a nutshell. Let's look at a few points...
"The Earth seems to be habitable for perhaps 6.29 billion years (Gyr), but this is excluding the influence of humans and our pesky habit of pumping extra CO2 into the atmosphere,"
Nonsense. Current science (though not the biased IPCC) clearly shows that extra CO2 changes little, and that little is likely to be beneficial.
Rushby suggests that future exoplanetary investigations – "or SETI campaigns" – might do well to focus on such planets, since the evolution of intelligent life is likely not a simple, few-billion-year affair.
An odd statement. We know that life started on our planet incredibly early. The earliest evidence for life found so far is in a 3.8 billion-year-old rock, the Isua sediments, found in western Greenland. So it appears life was underway at least within 700 million years of the formation of the Earth (4.5 billions years ago). Maybe life had an even earlier foothold on the planet but the traces have long since been wiped out.
...if we want to search for extraterrestrial intelligence, it would be wise to rigorously analyze planets that have been around for awhile for evidence of, for example, organisms that have altered their planet's biosignatures to such an extent that they could be detected across interstellar space, since those life forms would "undoubtedly require some level of complexity beyond that of simple replicating molecules."
Completely incorrect! For example, man has hardly altered the biosphere at all. In contrast, the early atmosphere had huge amounts of CO2 and NO oxygen. This was completely reversed by the activity of microbes, typically photosynthetic blue-green algae. Even today their impact on CO2 swamps human activity. And they have no intelligence.
If you want to detect intelligence, look for non-natural phenomena. Light from dark places, perhaps, or modulated radio waves.
So this paper seems to have got every aspect of the argument wrong...