Mars had 3/4 billion more years to develop, compared with the Earth. Mars formed first, and cooled first due to its smaller size.
One of the outstanding problems in astrobiology I mention is that the Earth was inhospitable until 3.8Gya, and the oldest fossils of presumably DNA based life (since it matches existing life we can study) was 3.7Gya. Mars was hospitable ~4.5Gya. So either life emerged IMMEDIATELY on Earth and did a complexity speed run before slowing down and remaining stagnant for the next billion years or so, or it emerged on Mars first and Earth was seeded once it was cool enough.
One of the outstanding problems in astrobiology I mention is that the Earth was inhospitable until 3.8Gya, and the oldest fossils of presumably DNA based life (since it matches existing life we can study) was 3.7Gya. Mars was hospitable ~4.5Gya. So either life emerged IMMEDIATELY on Earth and did a complexity speed run before slowing down and remaining stagnant for the next billion years or so, or it emerged on Mars first and Earth was seeded once it was cool enough.