In the brain, when neurons fire off electrical signals to their neighbors, this happens through an "all-or-none" response. The signal only happens once conditions in the cell breach a certain threshold.
Earth Sciences
Jul 08, 2019
30
6703
When an asteroid smacked into the Earth 66 million years ago, it triggered mass extinctions all over the planet. The most famous victims were the dinosaurs, but early birds, insects, and other life forms took a hit too. The ...
Evolution
Jun 28, 2019
2
2
Paleontologists are trying to dispel a myth about what life was like when dinosaurs roamed the Earth. The false narrative has wormed its way into books, lectures and even scientific papers about this long-ago era.
Plants & Animals
Jun 21, 2019
0
3
A new study shows how marine life around Antarctica returned after the extinction event that wiped out the dinosaurs.
Archaeology & Fossils
Jun 19, 2019
0
195
Up to 1 million species may go extinct due to human activity according to a recent report, some within decades. We all know the mammals in trouble—polar bears, giant pandas and snow leopards—but how many of us could name ...
Plants & Animals
Jun 06, 2019
0
273
Just as scientists are starting to understand the life forms and landscape of the ocean, they are also coming to grips with the threat of mass extinctions, speakers said at a marine biodiversity forum last week.
Ecology
Jun 04, 2019
1
11
It was framed as "the climate election," but last week Australia returned a government with climate policies that make the task of building a zero-emissions, safe climate Australia even harder.
Environment
May 23, 2019
0
17
More than a million species are at risk of extinction according to a new report on biodiversity. But even some species that aren't considered endangered may be less safe than people think. A new study published in the Journal ...
Ecology
May 15, 2019
0
7
Humans are causing the Earth's sixth mass extinction event, with an estimated one million species at risk of extinction.
Ecology
May 10, 2019
0
9
Diplomats and scientists from 132 nations wrapped up six days of negotiations in Paris Saturday over the wording of a landmark report on the dire state of Nature and its impact on humanity, a UN official told AFP.
Environment
May 04, 2019
0
15
An extinction event (also known as: mass extinction; extinction-level event, ELE) is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:
Over 99% of species that ever lived are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land organisms.
Since life began on earth, several major mass extinctions have significantly exceeded the background extinction rate. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others as it marks the extinction of nearly all dinosaur species, which were the dominant animal class of the period. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were mass extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record.
Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the threshold chosen for describing an extinction event as "major", and the data chosen to measure past diversity.
This text uses material from Wikipedia, licensed under CC BY-SA
