No… Martian Muddy Waters is not an extraterrestrial blues musician. It’s just a catchy title that links Mars, mud and water together.
The network of cracks in this Martian rock slab called “Old Soaker” may have formed from the drying of a mud layer more than 3 billion years ago. The view spans about 3 feet (90 centimeters) left-to-right and combines three images taken by the MAHLI camera on the arm of NASA’s Curiosity Mars rover. Credits: NASA/JPL-Caltech/MSSS
Guest post by David Middleton
Clear as mud: Desiccation cracks help reveal the shape of water on Mars
BOULDER, CO, USA: As Curiosity rover marches across Mars, the red planet’s watery past comes into clearer focus.
In early 2017 scientists announced the discovery of possible desiccation cracks in Gale Crater, which was filled by lakes 3.5 billion years ago. Now, a new study has confirmed that these features are indeed desiccation cracks, and reveals fresh details about Mars’ ancient climate.
“We are now confident that these are mudcracks,” explains lead author Nathaniel Stein, a geologist at the California Institute of Technology in Pasadena. Since desiccation mudcracks form only where wet sediment is exposed to air, their position closer to the center of the ancient lake bed rather than the edge also suggests that lake levels rose and fell dramatically over time.
“The mudcracks show that the lakes in Gale Crater had gone through the same type of cycles that we see on Earth,” says Stein. The study was published in Geology online ahead of print on 16 April 2018.
The researchers focused on a coffee table-sized slab of rock nicknamed “Old Soaker.” Old Soaker is crisscrossed with polygons identical in appearance to desiccation features on Earth. The team took a close physical and chemical look at those polygons using Curiosity’s Mastcam, Mars Hand Lens Imager, ChemCam Laser Induced Breakdown Spectrometer (LIBS), and Alpha-Particle X-Ray Spectrometer (APXS).
The Geological Society of America
“Old Soaker: Mastcam image of the Old Soaker rock slab taken on Sol 1555. The red-toned bed is covered by ridges that are the remnants of sediment that filled cracks that formed in drying lake in Gale Crater some ~3.5 billion years ago. The slab is about 80 cm across.” GSA
Mudcracks are very interesting for two reasons. They indicate that:
- Water was present in the past.
- Mud was present in the past.
The mud is actually more interesting than the water.
Early land plants led to the rise of mud
Mud rocks increased in riverbeds as rootless plants spread around 458 million years ago
BY CAROLYN GRAMLING, MARCH 1, 2018
Magazine issue: Vol. 193, No. 6, March 31, 2018, p. 9
Early plants made Earth muddier. Ancient riverbed deposits of mud rock — rocks containing bits of clay and silt smaller than grains of sand — began increasing around 458 million years ago, around the time that rootless plants became common across Earth, researchers say.
Anecdotally, geologists have long noted that early sediment deposits became muddier at some point, and suggested a connection with plants (SN: 6/22/74, p. 398). But no one had ever pinpointed when that muddening happened.
So geologists William McMahon and Neil Davies, both of the University of Cambridge, decided to look for when amounts of mud rock began increasing in 704 ancient river deposits from 3.5 billion to 300 million years ago. The researchers searched through nearly 1,200 published papers for data on mud rock in river deposits, and collected new field data at 125 ancient river outcrops. At those outcrops, the researchers calculated the percent of mud rock in the overall deposit by measuring the thickness of the muddy layers compared with the thickness of layers containing larger grains such as sand.
The resulting fractions showed the median mud content was about 1 percent before around 458 million years ago. At that point, the mud content steadily increased over about the next 100 million years or so to reach a median of about 26 percent in outcrops dated 359 million to 299 million years old, McMahon and Davies report in the March 2 Science.
That steady upsurge suggests that neither cyclical nor episodic forces — such as glacial-interglacial changes or tectonic events — could have driven the increase in muddiness. Instead, plants are the likeliest culprit. A primitive group of rootless plants called bryophytes, which includes modern mosses and liverworts, had likely become common by about 458 million years ago. Rooted plants further increased the mud content when they arose and began to spread around 430 million years ago, eventually forming great forests about 382 million years ago.
Update – From the actual paper
The article isn’t exactly right, the correlation is of the appearances of mudrocks and deeply-rooted plants.
Evolution of alluvial mudrock forced by early land plants
William J. McMahon,
Neil S. Davies*
Science 02 Mar 2018:
Vol. 359, Issue 6379, pp. 1022-1024
Mudrocks get a vegetative assist
Mudrocks such as slate and shale are rarely found in stratigraphy older than about 500 million years. McMahon and Davies compiled a large database of mudrock occurrence over the past 3.5 billion years to help assess the origin of this ubiquitous rock type (see the Perspective by Fischer). Mudrocks appeared at the same time as did deep-rooted land plants. The interplay between plants and sedimentary rocks suggests that a change in erosion rate and the chemistry of sediments delivered to the oceans occurred around 500 million years ago.
However, land plants do promote the production of clay minerals and the depth of chemical weathering profiles by increasing atmosphere-substrate connectivity through rooting, through the direct secretion of organic acids and chelates, and by developing symbiotic relationships that increase the capacity of cyanobacteria and fungi to dissolve soil grains (2, 18, 21–26).
The timing relative to the appearance of plants is unlikely to be a coincidence, as plants can greatly contribute to the development and retention of alluvial mudrocks.
A fuller understanding of mudrock in the absence of vegetation is a prerequisite for any studies that invoke ancient terrestrial mudrock strata as a primary archive of geochemical or petrological data and will have implications for understanding the context and nature of mudrocks that are increasingly detected on nonvegetated planets such as Mars (8, 37).
The primary building block of mudrocks are clay minerals and Mars has an abundance of clay minerals, much more abundant than expected.
Clay Minerals on Martian Surface Are More Abundant Than Expected
By Sarah Miller Dec 21, 2012
Clay minerals are found to be more abundant on the Martian surface than previously thought, according to a new study co-authored by the Georgia Institute of Technology.
Clay minerals are rocks that are formed when water is present for long periods of time. The presence of clay minerals on Mars was first discovered in 2005, indicating that the planet once hosted liquid water on the surface.
Now, a team of researchers has found that the planet is hosting more clay minerals than expected. The research team has detected the presence of clay in some of the rocks studied by Opportunity Rover when it landed at Eagle crater in 2004. But the rover detected only acidic sulfates in the rocks and since then moved to Endeavour Crater, a place NASA’s Mars Reconnaissance Orbiter pinpointed for clay minerals.
Using spectroscopic analysis from the Mars Reconnaissance Orbiter, the research team was able to identify the clay minerals at Eagle crater. They also found that clays also exist in the Meridiani plains, through which the rover trekked towards its current position.
“It’s not a surprise that Opportunity didn’t find clays while exploring,” James Wray, a faculty member at the Georgia Institute of Technology and a member of Curiosity’s science team, said in a statement.
“We didn’t know they existed on Mars until after the rover arrived. Opportunity doesn’t have the same tools that have proven so effective for detecting clays from orbit.”
Prior to the Mars Reconnaissance Orbiter’s discovery of clay minerals, they weren’t even looking for them. The Opportunity Rover wasn’t equipped to identify clay minerals.
While this doesn’t necessarily mean that plant life once existed on Mars, it does elevate the probability a bit. And, ironically, the mudrocks are actually the best places to look for evidence of past life on Mars. Now if we can just find those rascally Silurians.