# data[].attributes.attachment_link.readable_text
Five times in Earth's history, some three-quarters of all living species disappeared forever - and within a short period of time. These mass-extinction events marked the boundaries between different periods in geologic time. Those species losses reflect a major shift in the planet's ecology. Clues to these shifts can be seen in the fossils and rock layers that form part of the geologic record.

Today, human activities are driving species to go extinct at a rate never before seen.

And this loss of species really does matter, says Anita Narwani. She's an ecologist at the University of Michigan in Ann Arbor. That's because the diversity of species in an ecosystem - the breadth of different organisms present - provide people with all types of services we can't do without.

Trees provide oxygen for us to breathe. At the same time, they remove carbon from the air. That carbon is a contributor to global warming. Plants clean pollutants from air and water. Microbes break down waste. Animals disperse seeds that keep forests thriving. A broad range of living resources also provides people with food, shelter and medicine.

Narwani wanted to find out just how important biodiversity is for people. So she teamed up with other ecologists to review more than 1,700 studies. They found that more diverse parts of the globe tend to excel at things like removing carbon and providing us with wood and other natural resources. They also were better at keeping fisheries large and healthy so that they could feed many people.

Cicero Moraes/Wikimedia Commons (CC BY-SA 3.0)

The findings suggest people benefit greatly from there being a diverse range of species.

Unfortunately, biodiversity is in steep decline.

It is too soon to declare that Earth is undergoing a sixth mass extinction, Narwani says. She defines a mass extinction as the loss of 75 percent of species over 2 million years or less. We haven't lost that many - at least not yet. But if current rates of species losses continue, such a mass extinction could occur in just 300 years.

"This is a very short time relative to the time frame for the previous mass events," she points out. Such an event would leave a telltale absence of many species in the fossil record. From that point on, fossils of the vanished species would no longer appear in the pages of Earth's rock-based diary.

The new findings highlight the potential for humans to erase many of the resources on which we now depend. As people learn more, however, they can take steps to lessen those risks. For example, by using natural resources more efficiently, says Narwani, people can preserve ecosystems so that they can continue to provide us with their services.

Power Words
More About Power Words

biodiversity The number and variety of organisms found within a geographic region.

carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

diversity (in biology) A range of different life forms.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem A group of interacting living organisms - including microorganisms, plants and animals - and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

extinction The state or process of a species, family or larger group of organisms ceasing to exist.

fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called "body fossils." Things like footprints are called "trace fossils." Even specimens of dinosaur poop are fossils.

geologic time The span of time that covers Earth's 4.5 billion-year history. Scientists divide geologic time into successively briefer intervals of time, called eons, periods, epochs, eras and ages.

geologic record Mineral deposits and fossils that form in rock. Geologists can "read" these minerals to decipher what Earth's climate and geology was like (such as dry spells, earthquakes or volcanic eruptions) when the rock's ingredients were laid down. Fossils and other mineral can signal what life may have existed at the same time.

geology The study of Earth's physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. Planetary geology is the science of studying the same things about other planets.

global warming The gradual increase in the overall temperature of Earth's atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

mass extinction Loss of 75 percent of the world's species in a short time period, typically defined as 2 million years or less. Our planet has experienced 5 known mass extinctions.

microorganism,or microbe A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

Quaternary Period A time in the distant past that was defined by regular ice ages. It began about 2.58 million years ago. Scientists refer to its earliest period as the Pleistocene. Then, about 11,700 years ago, a second period began, known as the Holocene. It continues through today.

species A group of similar organisms capable of producing offspring that can survive and reproduce.

Alison Pearce Stevens is a former biologist and forever science geek who writes about science and nature for kids. She lives with her husband, their two kids and a small menagerie of cuddly (and not-so cuddly) critters.

# data[].attributes.attachment_link.description
Five times in Earth's history, some three-quarters of all living species disappeared forever - and within a short period of time. These mass-extinction events marked the boundaries between different periods in geologic time. Those species losses reflect a major shift in the planet's ecology.

# data[].attributes.attachment_link.readable_text
On May 19, 2010, at Joint Base Balad, north of Baghdad in Iraq, someone brought U.S. service member Jonathan Trouern-Trend a frog in a plastic bottle. The brightly colored amphibian had been hiding out in an unlikely place: the latrine.

Many on base knew Trouern-Trend as "the guy to identify critters," he said. A lifetime nature lover, he was on his second tour of duty in Iraq as a sergeant.

Before releasing the frog into a nearby pond, Trouern-Trend uploaded a picture of it to the mobile app iNaturalist, which connects a worldwide community of people who report sightings of animals and plants online.

App users informed him that he'd found a l emon-yellow tree frog (Hyla savignyi)-and noted that scientists had never recorded one outside of Kurdistan (map). The species' known range had suddenly expanded.

This kind of citizen science has exploded in recent years because of smartphones. Now, according to a new review of research about Earth's biodiversity, it's giving conservationists hope that new technology can slow extinctions. (See: " 5 Surprising Drone Uses (Besides Amazon Delivery).")

That's good news, because according to a review published on May 29 in the journal Science, current extinction rates are up to a thousand times higher than they would be if people weren't in the picture.

Study leader Stuart Pimm, a conservation ecologist at Duke University and contributor to National Geographic's News Watch blog, and his colleagues analyzed various data sources-in particular the International Union for Conservation of Nature's Red List of Threatened Species, a global inventory of species-to produce the first major review of extinction data. (See: " 20,000 Species Are Near Extinction: Is It Time to Rethink How We Decide Which to Save?")

Mobile apps, GIS satellite data, and online crowdsourcing, Pimm says, may be a partial antidote to the problem. Through these technologies, "we're mobilizing millions of people around the world, and we're on the cusp of learning very much more about where species are than we have ever known in the past." That's critical, he explains, because now "we know where the species are, we know where the threats are, and-even though the situation is very bleak-we are better able to manage things."

Peter Crane, dean of Yale's School of Forestry and Environmental Studies, said by email that the new "paper does huge service in pulling together the latest thinking on species extinctions for very diverse groups of organisms."

Crane, who was not involved in the study, agreed that new technologies like remote sensing and more comprehensive databases "will not only improve the effectiveness of conservation investments, but will also strengthen monitoring of change in species-level biodiversity through time."

How Many Out There?

Calculating extinction rates can be difficult, in part because no one knows exactly how many species there are. Scientists have identified at least 1.9 million animal species, and possibly millions more have yet to be named. And according to the study, at least 450,000 plant species likely exist.

Pimm says conservationists can calculate the extinction rate of the known species by keeping track of how many die out each year.

The technique is similar to that used to figure out a country's death rate: track the number of people who die in a given population each year, scaled to that population. Mortality rates are usually calculated as the number of deaths per thousand people per year.

Applying the same statistical approach to extinction data revealed a rate of 100 to 1,000 species lost per million per year, mostly due to human-caused habitat destruction and climate change. (See: " 7 Species Hit Hard by Climate Change-Including One That's Already Extinct.")

To calculate the rate of extinction before modern humans evolved, about 200,000 years ago, Pimm and his colleagues reviewed data from fossil records and noted when species disappeared, then used statistical modeling to fill in holes in the record. That analysis revealed that before humans evolved, less than a single species per million went extinct annually.

The study authors suspect that the extinction rate will only increase if trends continue-possibly resulting in what scientists call the sixth mass extinction in Earth's history. (Related: " The Sixth Extinction: A Conversation With Elizabeth Kolbert.")

Another conclusion of the study that can't be ignored, says Yale's Crane, is "that there remain huge gaps in knowledge. At least for the most diverse groups of organisms on Earth, the urgent need to clarify how many species there are, where they live, and how their populations are changing remains a key impediment."

People Power

To Jenny McGuire, a postdoctoral research scientist at the University of Washington's School of Environmental and Forest Sciences who wasn't involved in the study, the results aren't surprising.

Though some might quibble about the exact rate, she says, "in general scientists are in agreement that we're at a period of heightened extinction risk and rates, and that's been occurring nearly since humans have come onto the landscape."

McGuire sees the new study as a "really excellent call to arms" for people to act to prevent more species from vanishing.

She says that people can vote for policies that lessen the impact of climate change, which is hitting the oceans particularly hard by raising the water's pH and dissolving the shells of many marine animals. People can also encourage their governments to connect one nature reserve to another.

Pimm says protected areas, the "frontline of conservation," have kept extinction rates of mammals, birds, and amphibians 20 percent lower than they would have been without refuges. Nearly 13 percent of Earth's land has been set aside, but only 2 percent of the ocean is part of a refuge.

Pimm and colleagues noted that global databases and crowdsourcing are helping to fill in blanks by tracking biodiversity outside of protected areas, where species tend to be less studied. (Also see " The Ethical Flap Over Birdsong Apps.")

And of course anyone can contribute by becoming a citizen scientist like Trouern-Trend, who said he's part of a "a niche of people who want to help out" by giving conservationists a snapshot of our world. "From fungus to birds to plants," he said, "it's all interesting to me."

Follow Christine Dell'Amore on Twitter and Google .

# data[].attributes.attachment_link.title
Species Extinction Happening 1,000 Times Faster Because of Humans?

# data[].attributes.attachment_link.description
On May 19, 2010, at Joint Base Balad, north of Baghdad in Iraq, someone brought U.S. service member Jonathan Trouern-Trend a frog in a plastic bottle. The brightly colored amphibian had been hiding out in an unlikely place: the latrine. Many on base knew Trouern-Trend as "the guy to identify critters," he said.

# data[].attributes.attachment_link.title
What’s The Best Way To Stop Mass Extinction?