Martians are we?

While channel surfing, I ran across a science documentary called "Miracle Planet." In it, the early stages of the Earth were explored. While I knew about planetary accretion, I apparently didn't understand the implications of such a process. Accretion isn't just a bunch of dust coming together to make a doughy planet. It's smaller rocky bodies smashing together with larger ones. It's an apocalyptic process worthy of Jerry Bruckheimer treatment.

Consider first that Earth is the largest of this solar system's rocky worlds. Unless by some weird chance Earth attracted unusually larger rocks faster than the other worlds, Earth had more world-shattering collisions with planetoids than Mars, Venus or Mercury. These collisions would have sterilized the surface of Earth, but not necessarily killed all life on the planet (see below).

Also note that Mars is much smaller than Earth and so has probably had fewer sterilization events. We also believe that Mars was once a bit more habitable than it is now, although water seems to be present on Mars even today. It isn't a big stretch to think about Martian microbes living in the icy dust of Mars's soil. We have microbes on this planet living in harser conditions.

Life is tenacious. We are just now learning about extremophiles, those remarkable creatures that live without the "necessities" of life. It is no longer inconceivable that microbes inside a meteor could survive planetfall.

Life may have started many times on this planet, only to be eradicated during accretion. Could life have evolved on Mars only to be transported to Earth? Is that why all life derives from one genetic tree? Has Mars saved our collective bacon from the consequences of our ponderous girth?

This is an extraordinary claim. Is this even feasible? Even if E.T. bugs fell to Earth, why were they not sterilized during accretion? Did the life bearing rocks come to Earth after the last "global reset?" That's possible, but requires a little too much good timing for my liking. Instead, we can suppose that life hid deep under ground while the world burned.

New research suggests that even when the Earth was in the throes of accretion, the horrific global heat didn't penetrate to the mantle over the continents (although this isn't the case were the crust is thin, like at the bottom of oceans [whose water would have boiled away during these hellish events]). The study suggests that a Goldilocks region in the crust would have kept extremophile life happy enough.

Is this why terrestrial life is all related? There is only one genetic tree to which we all belong. Did that tree spring from a Martian seed?