The moon and Earth went through a period of bombardment, which stopped after 3.8 billion years. Afterwards, single-celled organisms came into being and existed for 3 billion years. Astrobiologists wonder if this stasis is characteristic of another biology elsewhere. After 3 billion years, there was a remarkable growth in the number of species. Thus, you may be much more likely to find microbial life in the search for extraterrestrial life.
Thermopiles are the oldest organisms.
Maybe the earliest organisms didn't start with a nice tepid pond but in extreme conditions. After all, Earth was hotter during the period after the bombardment ceased. In Eastern Washington one mile beneath basalt, there are bacteria that live off the hydrogen given off by basalt. The water has been there for as long as 100,000 to l million years. These bacteria have their own ecological niche.