It’s a bit worrying when a scientific paper begins, “How long will life on Earth survive?” But in this case—a study by Jacob Haqq‐Misra of Blue Marble Space and Eric Wolf at the University of Colorado Boulder—the billion-plus-year timeline under consideration shouldn’t cause you too much existential panic.

The context for this question is that we understand the Sun will brighten as it eventually matures into a red giant that swallows the Earth in a solar furnace. So, where along that 5 billion-year path will life on Earth, in fact, be cooked?

Weathering and the weather

This isn’t just a question of incoming radiation. Among the thermostat-like stabilizing feedback loops in Earth’s climate, the cycling of CO₂ through the solid Earth is a major factor over timescales this long. The weathering of silicate rocks at the surface converts atmospheric CO₂ into carbonate that ends up on the seafloor, where it can be subducted into the mantle with tectonic plates. (And eventually, it can cycle back out to the atmosphere through volcanoes.)

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We tend to view ourselves and the complex cells that build us as a distinct branch of the tree of life from the compact, seemingly featureless cells of bacteria and archaea. But we've found that our genome is actually a hybrid, a mish-mash of genes from bacteria and archaea, along with some that have evolved in our own lineage.

Scientists gradually settled on a simple explanation for this: the first complex cells were the product of a fusion between archaeal cells and bacteria, with the bacteria ultimately evolving into the mitochondria, a chemical-power-generating structure that still retains a bit of its own genome. Over time, many of the other bacterial genes were transferred to the nucleus of what was becoming what we now call a eukaryote, intermingling with the archaeal genes there.

But a new study has taken a careful look at some of the genes shared by all eukaryotes and comes to the conclusion that the reality is a little more complicated and that there were several waves of gene transfers from bacteria. The big picture of a merger between bacteria and archaea is still right, but it was only part of a picture where gene transfers among species were commonplace.

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