How did life begin on Earth? While scientists have theories, they don’t yet fully understand the precise chemical steps that led to biology, or when the first primitive life forms appeared.

But what if Earth’s life did not originate here, instead arriving on meteorites from Mars? It’s not the most favoured theory for life’s origins, but it remains an intriguing hypothesis. Here, we’ll examine the evidence for and against.

Timing is a key factor. Mars formed around 4.6 billion years ago, while Earth is slightly younger at 4.54 billion years old. The surfaces of both planets were initially molten, before gradually cooling and hardening.

Life could, in theory, have arisen independently on both Earth and Mars shortly after formation. While the surface of Mars today is probably uninhabitable for life as we know it, early Mars probably had similar conditions to the early Earth.

Early Mars seems to have had a protective atmosphere and liquid water in the form of oceans, rivers, and lakes. It may also have been geothermally active, with plenty of hydrothermal vents and hot springs to provide the necessary conditions for the emergence of life.

However, about 4.51 billion years ago, a Mars-sized, rocky planet called Theia crashed into the proto-Earth. This impact caused both bodies to melt together and then separate into our Earth and its moon. If life had begun before this event, it certainly would not have survived it.

Mars, on the other hand, probably didn’t experience a global remelting event. The red planet had its fair share of impacts in the violent early solar system,........

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