No… Martian Muddy Waters is not an extraterrestrial blues musician. It’s just a catchy title that links Mars, mud and water together.
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).
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.