Am manager, hate should.
Should presumes an ideal set of conditions with perfect context.
Could is a much better term as it implicitly accepts real world conditions and a lack of total context by couching the affirmation as contingent upon only the discussion (and prior references) at hand.
You think so? Earth and the Sun are only about 5 billion years old, or 1/3 the age of the universe. Life is estimated to have appeared on Earth about 4 billion years ago.
Under the law of averages, life could have independently developed and reached comparable maturity to Earth at least two other, non-concurrent times. We're third generation at best.