Tree adapted from Upham, N. Inferring the mammal tree: Species-level sets of phylogenies for questions in ecology, evolution, and conservation. PLoS Biol 17, e More Details Learn more about adaptive radiations , in which a lineage rapidly diversifies and the newly formed lineages evolve different adaptations.
Previous Detecting mass extinctions in the fossil record. Next Correcting common misconceptions about mass extinctions. Footer Connect Email Facebook Twitter. Over long periods of time, the number of species becoming extinct can remain fairly constant, meaning that an average number of species go extinct each year, century, or millennium.
These extinctions have had widely different causes. About million years ago, a great expansion occurred in the diversity of multicellular organisms. Paleobiologists, scientists who study the fossils of plants and animals to learn how life evolved, call this event the Cambrian Explosion.
Since the Cambrian Explosion, there have been five mass extinctions, each of which is named for the geological period in which it occurred, or for the periods that immediately preceded and followed it.
The first mass extinction is called the Ordovician-Silurian Extinction. It occurred about million years ago, at the end of the period that paleontologists and geologists call the Ordovician, and followed by the start of the Silurian period. In this extinction event, many small organisms of the sea became extinct. The next mass extinction is called Devonian extinction, occurring million years ago during the Devonian period. This extinction also saw the end of numerous sea organisms.
The largest extinction took place around million years ago. Although life on Earth was nearly wiped out, the Great Dying made room for new organisms, including the first dinosaurs. About million years ago, between the Triassic and Jurassic periods, came another mass extinction.
By eliminating many large animals, this extinction event cleared the way for dinosaurs to flourish. Finally, about This is the famous extinction event that brought the age of the dinosaurs to an end. Those niches allowed for new groups of organisms to thrive and diversify, which produced a range of new species.
In the case of the Cretaceous extinction, the demise of the dinosaurs allowed mammals to thrive and grow larger. Scientists refer to the current time as the Anthropocene period, meaning the period of humanity.
They warn that, because of human activities such as pollution, overfishing, and the cutting down of forests, the Earth might be on the verge of—or already in—a sixth mass extinction. If that is true, what new life would rise up to fill the niche that we currently occupy?
The period ended with extinction of the dinosaurs and the rise of mammals. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited. Tyson Brown, National Geographic Society. Our effect on the process of evolution even extends to our own species' evolution. Technology and culture have protected us to a great extent from the selective pressures that drive evolution, allowing many people -- especially those in developed nations who, without medical intervention, would not live to reproductive age -- to pass their genes on to the next generation.
Other scientists note that technology and culture have changed but not eliminated the role of natural selection on our species. We now adapt to crowding, pollution, and new disease rather than the necessity to escape from large predators. Humans will change in the future, but are unlikely to evolve into a new, separate species because no human group is truly isolated anymore, given our transportation systems.
Without genetic isolation, there is no further opportunity for speciation among humans. Learn More The Evolving Enemy.
Humans did not evolve from present-day apes. Rather, humans and apes share a common ancestor that gave rise to both. This common ancestor, although not identical to modern apes, was almost certainly more apelike than humanlike in appearance and behavior. At some point -- scientists estimate that between 5 and 8 million years ago -- this species diverged into two distinct lineages, one of which were the hominids, or humanlike species, and the other ultimately evolved into the African great ape species living today.
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