3 Early Life on Earth and Analogies to Mars

Abstract

One of the prime necessities of life is liquid water [87]. The presence of liquid water on a planet therefore naturally leads to the question of whether that planet hosted or still hosts life. Although there is much dispute at the moment as to how much water Mars had in its early history and at what temperature, there is sufficient evidence for its presence in substantial quantities in the form of geomorphological features [1–4], as well as the evidence for aqueous alteration of minerals in the Martian meteorites [Chap. 1 by Baker et al., 5–7] and possibly water-lain hematite [8, 9], to stimulate hypotheses regarding the possibility of life on Mars. This chapter will concentrate on the possibility of life having arisen on Mars early in its (watery) history using, as the closest analogy in time and environmental conditions, the early Earth and early terrestrial life. I will state at the outset that, given the rarity of rock remains from the early Earth’s history, there is a heated debate at the moment concerning the early environmental conditions of the Earth during the Hadean (4.56 – 4.0 Ga ago) and early Archaean (4.0 – 3.2 Ga ago), not to speak of whether life already existed on Earth before 3 Ga ago and in what form [10, 11]. In the following, I will review of the situation to date, present the evidence for life by about 3.5 Ga ago, and then examine the relevance of early Earth studies for Mars.