Christie Wilcox in Quanta:
Our planet formed a little over 4.5 billion years ago, and if the most recent estimates are correct, it wasn’t long before life arose. Not much is known about how that happened because it’s maddeningly difficult to investigate. It’s also proved tough to study what happened next, during the first billions of years of evolution that followed, when the main domains of life emerged.
A particularly vexing mystery is the rise of the eukaryotes, cells with well-defined internal compartments, or organelles, which are present only in animals, plants, fungi and some microbes like protists — our evolutionary kin. The earliest eukaryotes left no clear fossils as clues, so researchers are forced to deduce what they were like by comparing the structural and molecular details of later ones and inferring their evolutionary relationships.
Right now is “an incredibly exciting time” for such research, said Michelle Leger, a postdoctoral fellow at the Institute of Evolutionary Biology in Barcelona, Spain. With modern genetic sequencing technologies, scientists can read the entire genomes of diverse life forms, and as microbial life is revealed in ever-increasing detail, new species and other taxonomic groups are coming to light. With that wealth of data, researchers are tracing lineages of organisms backward through time.