\n<\/p>\n
While scientists often test these chemistries by whipping them up in the lab, Ka\u00e7ar explores what alien life might look like a little differently. Rather than just trying out ingredients, she focuses on the recipe.\u00a0<\/p>\n
For life, that means genomes. By looking at the genes of organisms today and reconstructing what their ancestors were like in the past, researchers can see how life\u2019s chemistry changed over time. They can pick out which parts of the recipe have been flexible and which parts have always been essential.\u00a0<\/p>\n
This process, called ancestral sequence reconstruction (ASR), uses computer models to predict the genomes of extinct species from their living descendants. Researchers can then study those genes to learn what long-dead organisms were once like. Scientists have learned when mammals evolved to be nocturnal, for instance, by tracing genes related to how sensitive we are to light.<\/p>\n
Ka\u00e7ar\u2019s team is among a handful who take this one step further. Instead of just predicting the genes of the past, they bring them back to life. They make real, living organisms express parts of their ancestors\u2019 genetic code.\u00a0<\/p>\n
So far, Ka\u00e7ar\u2019s group has mainly used ASR to track how microbes \u201cate\u201d carbon and nitrogen billions of years ago. Back then, our planet was very different, with almost no oxygen in its atmosphere and fewer ingredients for life available. ASR allows Ka\u00e7ar to access this version of Earth as a kind of alien world in itself \u2014 one that we know hosts life.\u00a0<\/p>\n
\u201cWe are able to imagine different atmospheres, different temperatures, different oceans,\u201d Ka\u00e7ar says.\u00a0<\/p>\n
Ka\u00e7ar\u2019s research has found instances where life\u2019s core chemistry seemed to change in response to its environment, but she has also been surprised to discover how much about life seems to be set early on. Ka\u00e7ar says it\u2019s like life was \u201cput on railroad tracks\u201d after a certain point. That would make understanding Earth\u2019s ancient conditions valuable in a whole new way.<\/p>\n
All of these exotic possibilities, including those contained within our past, are changing how we search for life beyond Earth.\u00a0<\/p>\n
Already, treating the ancient Earth like another planet has taught us about other worlds that might be out there. In a recent study, Ka\u00e7ar and her collaborators reconstructed aspects of the chemistry that ancient marine life once used to perform photosynthesis, then predicted how their signs of life would have looked from space. With this information, astronomers could decide not only if a planet looks like Earth today but if it looks like the kind of world that Earth was billions of years ago.\u00a0<\/p>\n
All of this is building to a more complete universal definition of habitability. By exploring different ingredients and recipes, scientists like Ka\u00e7ar are slowly defining the edges of a broader search for life. They are preparing us to interpret new signs of life, whether from a planet just like our own or from strange, undiscovered worlds.<\/p>\n
And if we don\u2019t find aliens? Life on Earth would be all the more special, and understanding how life formed here would be even more important.\u00a0<\/p>\n
\u201cUltimately, it will tell us more about ourselves,\u201d says Ka\u00e7ar. \u201cWhat better way to honor our own ancestors?\u201d<\/p>\n<\/div>\n