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Habitats where formerly only conifers, ferns, and their relatives grew were invaded by flowering plants that soon became the most common species, even in forests where giant ferns were still abundant as overstory trees. This time span, barely 3 percent of the entire timeline of life on Earth, also saw the origins or the diversification of many animal groups, including most of the animals that sing in modern ecosystems. Biologists refer to this period as the terrestrial revolution, a burst of creativity unrivaled since the great Ediacaran and Cambrian evolutionary explosions of the early oceans. It was also a time of revolutionary expansion in sound making. Insect diversity, especially, rapidly grew in concert with the rise of the flowering plants. This flourishing changed the sound of Earth, lifting old voices to prominence and catalyzing the origin of new groups of singing insects. For many of these singers, evolutionary history resembles a river flowing into a delta. A long single channel suddenly fans into a bush of rivulets that then further ramify. The channel is the ancestral lineage and the fan is the explosion of animal diversity that followed the ascendance of flowering plants on Earth. Katydids sing by drawing a plectrum at the base of one wing over a ridged file on the other. These first modern katydids descended from a lineage of ancestral crickets that stretches all the way back to Permostridulus’s time, at the dawn of cricket evolution nearly 300 million years ago. This long ancestry then burst into new forms starting after 100 million years ago, followed by another expansion in diversity after the asteroid impact and mass extinction 66 million years ago. 
Beyond The Blue
Katydids are mostly foliage eaters. A few feed on conifers and some species prey on other insects, but most are entirely dependent on flowering plants. Crickets and their kin sang long before the advent of flowering plants, and their sounds were likely the principal element of the animal soundscape from 300 to 150 million years ago. These ancient sounds, too, received a boost when flowers evolved. The true crickets, the Gryllidae, that now sing from meadows, forests, and lawns worldwide appeared 100 million years ago in the midst of the diversification of flowering plants. Grasshoppers are a much later addition to Earth’s soundscape. Although the grasshopper branch of the insect family tree broke away from its cricket cousins 350 million years ago, it was not until the Cretaceous, when flowering plants became abundant, that they started to sing. Grasshoppers then continued to diversify and add new singing members of their family alongside the ongoing expansion of flowering plants. The buzz, whine, and shriek of over three thousand modern cicada species come from the tymbal organ on the side of their abdomens. Within the organ, muscles pop fine corrugation back and forth, sometimes hundreds of times each second, yielding a crackling sound that is then filtered and amplified by resonant chambers in the abdomen. In warm climates worldwide, the unique structure of the tymbal defines the soundscapes of hot afternoons. The cicada clans that we hear today diversified after the rise of flowering plants, starting one hundred million years ago. Don't Let Yourself Down
The sound of this moss bug, a sonic living fossil, travels as vibrations through vegetation, a repeated low buzz transmitted through the insect’s legs. The ancestral lineages gave rise to the modern cicadas and moss bugs, but also to the spittlebugs, planthoppers, and treehoppers, a clan of over forty thousand species that feed like ticks on plants, using piercing mouthparts to draw nutritious juices from within. Almost all these species make sounds inaudible to us, usually by transmitting vibrations to the leaves or twigs on which they live. From ancient roots, the modern representatives of these groups ramified into their present diversity following the expansion of flowering plants. This relationship is both of the moment, fueled by the plants’ sugars and amino acids, and ancient, the result of the stimulus that flowering plants gave for the evolutionary diversification of these insect groups. Diversity in other major insect groups was also boosted by the rise of flowering plants. Ancestors of moths and butterflies lived three hundred million years ago, feeding on nonflowering plants. Tiny drumlike ears evolved at least nine different times among moths, mostly around one hundred million years ago, organs that are variously located on the abdomen, thorax, or proboscis, depending on the type of moth. These ears hear into the ultrasonic range and likely first evolved to avoid attacks from predaceous insects and birds. Such excellent hearing opened a new avenue for courtship, and many moths sing by softly rubbing their wings together, giving swishing, whispery songs too high for human ears to detect. But, unlike ours, moth ears can detect these sounds. Electrodes inserted into nerves running from these ears show that they can pick up sound up to sixty kilohertz, far above the twenty kilohertz that is the maximum for humans. The Night Of The Long Knives
The tiger moths went further and evolved bumps in their exoskeletons that, when buckled, release ultrasonic clicks. These sounds startle and jam the echolocating signals of hunting bats, and also signal the distastefulness of poisonous tiger moth species. This aerial sonic warfare is founded on the flowering plants that both feed the moths in the present day and stimulated the flaring of their species diversity long ago. Before flowering plants evolved, the soundscape of the terrestrial world comprised only a few insect voices, the crickets, stoneflies, and perhaps ancestors of the cicadas and treehoppers. By the late Cretaceous, the insect chorus was like that of our time, a diverse mix of katydids, crickets, grasshoppers, and cicadas. The Cretaceous climate was hot, what geologists call a greenhouse world of high carbon dioxide, and the land was cloaked with lush forests, even close to the poles. Likely this was the first time in the long history of Earth that the air thrummed and pounded worldwide with the communicative sounds of life. Like modern rain forests, late Cretaceous forests were animated night and day by the crepitations, drones, buzzes, shimmers, bleats, and whines of singing insects. Earth, finally, was wrapped in song.