Paleozoic, Mesozoic, and Cenozoic. These are the major eras in the history of life on Earth, and the transition from one period to another has been marked by a major turnover in fossils — one assemblage of organisms going extinct and being replaced by another.
Today paleontologists agree that the biggest extinction in the fossil record occurred at the transition between the Paleozoic and Mesozoic, about 250 million years ago. During this Permo-Triassic extinction, perhaps as much as 70 percent of the plant, reptilian, amphibian, and insect species died on land. In the ocean, the consequences were even more devastating; up to 96 percent of Earth’s marine species went extinct.
The cause of such a catastrophic loss of life has been the subject of ongoing study. One proposed explanation is an asteroid strike like the one blamed for dinosaur extinction 65 million years ago. Another explanation involves the oxygen level in the ocean. Marine organisms need oxygen just as terrestrial organisms do, and some scientists have speculated that oxygen-poor water welled up from the ocean depths and suffocated marine life. Another hypothesis is large-scale volcanism. Studies published in November 2011 and May 2012 argue that volcanism does the best job of explaining all the evidence in the geologic record. And it not only explains the ancient mass extinction, but also hints at future threats to ocean life.
Although weathered by 250 million years of erosion, the Siberian Traps remain unmistakable today. Photo by Jon Ranson, NASA.
The volcanic hypothesis centers around the Siberian Traps, flat-topped volcanic mountains in Russia. The massive eruption that produced these mountains occurred 250 million years ago, about the same time as the Permo-Triassic extinction. The eruption was one of the biggest volcanic events in the last 500 million years, and it matches up with not only the timing of the extinction, but with the kinds of animals that were hit hardest.
Volcanoes release carbon dioxide, and the Siberian Traps eruptions would have emitted huge quantities of it, while also producing it indirectly. The basalts released by the eruptions flowed over sedimentary rock rich in organic material. Geologic studies of the Siberian Traps have revealed gas explosion structures along the margins of the flood basalts, which geologists have interpreted as evidence of sudden, violent carbon releases from sedimentary rocks under pressure by lava.
Besides raising atmospheric temperatures with heat-trapping gas, the newly released carbon dioxide would also have affected the ocean. Carbon dioxide dissolves in seawater to create carbonic acid, increasing ocean acidity. The carbonic acid reacts with carbonate ions, leaving less carbonate for marine life to use for shells or skeletons. Animals with such shells or skeletons suffer, but they don’t all suffer equally. Mollusks and marine arthropods have what biologists refer to as “buffered physiology,” which means they have closed circulation systems and/or gas-exchanging features (such as gills) to buffer their internal tissues from changes in ocean chemistry. Other animals such as sponges, corals, sea urchins, and sea lilies do not; their tissues are directly exposed to seawater. What the Permo-Triassic extinction studies found was that the poorly buffered organisms experienced greater rates of extinction and took longer to rebound.
Likely to be among the biggest losers in ocean chemistry changes, corals have few mechanisms to protect their internal tissues from increasing acidity. Image courtesy NOAA Ocean Explorer.
Carbon dioxide alone did not cause the catastrophic extinction 250 million years ago. Other factors, including higher temperatures and lower oxygen levels in the water, also pressured marine life. But carbon dioxide likely played an outsized role.
No one can predict when volcanic activity as widespread and destructive and the Siberian Traps eruptions might occur again. But we do know that rising carbon dioxide levels in the atmosphere pose a threat to marine life today. While volcanoes currently release 130 to 380 million metric tons of carbon dioxide each year, human burning of fossil fuels releases about 30 billion tons of it. That’s anywhere from 100 to 300 times as much greenhouse gas that can increase ocean acidity.
Today’s ocean contains a sizable reservoir of fine-grained calcium carbonate sediment that acts as a counterweight to rising ocean acidity. Geologists surmise that such a reservoir probably didn’t exist in the Permo-Triassic ocean. Moreover, today’s marine organisms descended from the survivors of high acidity episodes over the last 250 million years, so they may be better able to withstand ocean chemistry changes. Nevertheless, rising ocean acidity could spell trouble for marine organisms such as corals. A 2011 study of volcanic carbon dioxide seeps in Papua New Guinea found that ocean acidification and temperature stress reduced coral diversity and abundance. As before, poorly buffered marine life could suffer.
In case you missed it, NASA is sponsoring a video contest starring your home planet. The winner will receive behind-the-scenes access to the launch of NASA’s next major Earth-observing satellite — the Landsat Data Continuity Mission (LDCM) — from Vandenberg Air Force Base in January 2013.
Most of the public tends to focus on NASA’s role in planetary science, astrophysics, solar science, astronomy, and space flight. But as Earth Observatory readers know, we also have huge role in studying the one planet that is most important to us all. This contest is a chance to show how and why we should study our planet from space, and what that view means to you. The theme of your video should be: “The Home Frontier.”
We would love to see some entries from EO readers. If you dig around in our archives, you will find more than 11,000 Earth photos, maps, animations, and data visualizations to work with. Just about all of them are in the public domain and free to use in your creations.
For all of the rules and guidelines, visit this page. The contest ends on May 31, 2012. As we all know, nothing motivates quite like a quick deadline…
P.S. — For some inspiration, here is the video that won last year’s contest:
We recently posted an image of a dust storm in the Middle East (see below) that prompted one of our Facebook followers to ask why the dust is thicker near the left part of the image than the right. He wondered if the layer of dust is usually thickest near the origin of dust storms.
I contacted Ralph Kahn, an atmospheric scientist at NASA Goddard who specializes in studying dust and other types of aerosols for an answer. Kahn quickly emailed back with a detailed explanation. At the end of his note, he even managed to toss in a reference to dust storms on Mars. Kahn’s full note (in italics and with imagery added) is below.
“The thickness of dust in the atmosphere depends on several factors. In simple situations, there are discrete sources, and a wind that blows steadily in one direction. In this case, you get a relatively thick plume near-source that eventually thins and dissipates downwind, as the plume broadens, and as some of the dust settles out of the atmosphere. An example of this on the Earth Observatory is here (see the image below).
Dust storm in the Saharan Desert. Image acquired by MODIS. Click on it for more details.
It is slightly more complex when the source is an extended area, and the wind still blows steadily in one direction. In this case, you can get a relatively thick plume near-source that again thins and dissipates downwind, but not so uniformly. Examples of this on the Earth Observatory are here, here, and here (see the three images below).
Here there is structure in the plumes, as there are multiple sources within the source regions whose plumes tend to merge, and some are more productive than others, which could be due to differences in the surface and/or in the near-surface wind. Moving downwind, there is some structure in the wind as well, most likely due to wind shear (different wind speeds at different elevations).
Dust storm in New Mexico. Image from the Crew Earth Observations Office. Click on it for more details.
Dust storm in Washington. Image acquired by MODIS. Click on it for more details.
Dust storm in the Saharan Desert. Image acquired by MODIS. Click on it for more details.
Combining multiple sources, changes in the near-surface wind speed and direction at some sources over time, differences in the speed or direction of the wind carrying the dust after it is lifted (which can occur at different *elevations* as well as different horizontal locations) and different rates of settling, any number of patterns can arise. (Note: Kahn gave us five examples, but I only included thesetwo. You can view the other three here, here, and here.)
Dust storm in Afghanistan. Image acquired by MODIS. Click on it for more details.
Dust storm in Kuwait. Image acquired by MODIS. Click on it for more details.
And sometimes dust heats up in the atmosphere, and actually convects, creating cumulus-like plumes. This is common on Mars, but can also occur on Earth.
Dust storm on Mars. Image from the National Optical Astronomy Observatory, Association of Universities for Research in Astronomy, and the National Science Foundation. Click on it for more details.
Dust storm on Mars. Image from NASA JPL. Click on it for more details.
Dust storm in Kazakhstan. Image from the International Space Station. Click on it for more details.
The Thematic Mapper — the primary natural-color imager on America’s venerable Landsat 5 satellite — officially ended regular operations on May 8, following several months of operator attempts to revive it. TM collected images for 27 years, and several hundred of them are part of our Earth Observatory archives. Landsat controllers are happy, however, to be collecting data once again from the Multispectral Scanner (MSS) on Landsat 5, an instrument that had not worked for nearly a decade. The next generation of Landsat is scheduled for launch in 2013.
NASA’s Earth Observer 1 (EO-1) satellite also broke off regular operations and went into a “safe mode” in April. But in that case, there is happier news.
EO-1 halted operations after experiencing a low battery charge. Like almost all satellites in earth orbit, EO-1 uses solar panels to generate electricity for its systems and to charge its batteries for orbits on the night side of Earth. Think of it like a mobile telephone that runs until the battery is low and then needs to be recharged. Except EO-1 gets drained and recharged and drained 14 times a day. Every day for the past decade.
The satellite also gets bombarded by space radiation, particularly while passing through the South Atlantic Anomaly, where electrically charged particles trapped by the Earth’s magnetic field graze deeper into the atmosphere than in other spots. The satellite also endures cycles of heating in direct sunlight and freezing in the shade…over and over again.
Low-Earth orbiting satellites like EO-1 are built to endure these cycles of charge and discharge, hot and cold, light and dark, radiation bombardment and calm vacuums. But it’s always a little amazing to think about how many variables those satellites are designed to survive.
After a few weeks of sleepless nights and long days, the NASA team was able to coax EO-1 back into operations by resetting everything on the satellite and reloading all of the flight and operations software. Think of it like reseting your computer by unplugging it and turning it back on. Granted, it’s a lot more complicated, and mission engineers had to be very sure they understood why the problem happened so it didn’t happen again right after the reset.
EO-1 has been back in operations for several weeks since its two week spring break. The “first/return to light” image above shows Christchurch, New Zealand, as viewed by the Advanced Land Imager (which was actually designed to test technologies for the next generation of Landsats). The satellite appears to be back in good health, but you can read more about the anomaly on the EO-1 satellite page. (Look for the document “EO-1 Safehold Anomaly 2012:097:23:59 2012:111:23:59” near the bottom of the page. If that seems cryptic, it’s an indication of the time of the anomaly: just shy of midnight on day 97 of 2012 (April 6) to day 111 (April 20)).
We often see our images and stories pop up in different places. Obviously we see Earth Observatory content showing up on other web-based science and news media or on television. But you might see our images in other places, too.
This past week a new iPhone/iPad app called Xweather was launched in the iTunes store. This app takes advantage of our Natural Hazards RSS feed to highlight event imagery around the Earth.
And a few weeks back, my wife and I were browsing through a fabric store when a particular pattern caught our eye: the Blue Marble (2000) on a quilt! This pattern is by Emily Cier of Carolina Patchworks.
Where have you seen images and stories from the Earth Observatory? Other apps? Posters? Uses in books? Hot air balloons? The Blue Marble gets quite a bit of use in advertising and other places (a quick search of Flickr provides several examples). Let us know what else you find…or what else you do with it yourselves.
We bring you this week’s indicator—90—with a sigh.
Ninety is the combined number of Earth-observing instruments on NASA and NOAA satellites that are currently monitoring our planet. And that number is about to plunge, according to a National Research Council report released in May 2012. By 2020, there could be less than 20 instruments in orbit, and the total number of missions is expected to fall from 23 to just 6.
Many of the these space-based instruments aren’t exactly household names. (MODIS, anyone? ASTER or ALI? AMSU-A or SORCE?) Still, they are our eyes and and ears on the planet, as indispensable to understanding how it works and changes as our human senses are to navigating life on the surface. Without these satellites, the United States would be blind to most Earth systems, unable to effectively monitor the effects of global warming and the constant parade of volcanic eruptions, wildfires, droughts, dust storms, hurricanes, crop health, air pollution.
The NRC study authors mince few words in explaining what the reduction would mean:
These precipitous decreases warn of a coming crisis in Earth observations from space, in which our ability to observe and understand the Earth system will decline just as Earth observations are critically needed to underpin important decisions facing our nation and the world. Advances in weather forecast accuracy may slow or even reverse, and gaps in time series of climate and other critical Earth observations are almost certain to occur.When these long-running data streams fall silent, users requiring these observations will go unsupported, and progress toward understanding the Earth system and how it supports life may stagnate.
It’s worth noting that the committee only counted missions that have been officially proposed, funded, and given a launch date. It did not include missions that will likely come to fruition but have not yet been fully funded (the successor mission to GRACE, for example). That means the future fleet might not be quite as small as feared, but even the most optimistic estimates indicate a major decline in observing capability.