Privileged Planet: the important evolution of mud (Introduction)

by David Turell , Monday, June 20, 2022, 05:04 (888 days ago) @ David Turell

Involved with the appearnce of plants on land:

https://knowablemagazine.org/article/living-world/2020/origin-mud?utm_source=email&...

"Magnify this effect globally, and the impacts would have been substantial — not just on coastal life but on the landscape of the entire planet. Before plants, rivers would have stripped continents of silt and clay — key constituents of mud — and sent these sediments to the seafloor. This would have left continents full of barren rock, and seas with smothered fish.

"Once plants arrived on land, things began to change. Mud clung to vegetation along riverbanks and stuck around rather than shuttling straight to the seafloor. Davies, now at the UK’s University of Cambridge, and his colleagues have found that the expansion of land plants between about 458 million and 359 million years ago coincides with a more than tenfold increase in mud on land — and a significant shift in the ways that rivers flowed. The arrival of first plants and then mud “fundamentally changed the way the world operates,” he says.

"Life evolved tools to cope with the new muckiness and new river shapes, resulting in a diversification of life and landscapes that persists to this day. Plants are responsible for much of this change, but mud contributed too, by adding a cohesiveness to the continents — unlike sand, wet mud sticks together.

***

"Before plants arrived on land, mud was around — it was just mostly sent to the seafloor by rivers. Once plants showed up, they not only held sediments in place but their roots also physically broke down rock and released chemicals that further crumbled it. In these ways, plants accelerated what geologists refer to as the “continental mud factory.”

***

'Those gravelly Alaskan rivers have many channels that braid across sand banks, continually slumping and forming more channels as they periodically overflow — like rivulets at the edge of a beach. Without anything anchoring these riverbanks in place, they continuously collapse to form new channels. But the arrival of plants kept that erosion at bay — and mud added to the riverbanks’ cohesion — so rivers were less likely to slump into these braided forms. Instead, they developed a single channel that meandered through the landscape in a cohesive “S” shape, like parts of the Mississippi and Amazon rivers do today. In this sense, the arrival of plants “is one of the best natural experiments in landscapes that has ever happened on Earth,” Perron says.

***

"To get through mud, an animal such as a worm creates cracks to shuffle through by contracting its body, extending it, squeezing water out of the way and moving forward. This is mechanically different from traveling through sand, which requires an animal to excavate material out of the way, Shillito says. So early land worms and insects would have had to evolve body parts equipped to deal with muckier movements.

"And those movements, in turn, could have helped shape the mud itself, says Lidya Tarhan, a paleobiologist at Yale University. “The act of digging and excavating those burrows and keeping them clear can move around sediments and change the distribution of sediments and also affect the chemistry,” she says. For example, some invertebrates ingest sediments to extract nutrition, and chemical reactions in their guts can form fine particles that come out in their feces as mud.

***

"Modern rivers that people have deforested show how the absence of vegetation can destabilize riverbanks and cause them to become less cohesive. Along California’s Sacramento River, for example, areas that farmers cleared for cropland are far more susceptible to erosion than areas that remain forested. Conservationists have worked to stabilize the river by planting more than a million seedlings along its banks.

"Understanding the interplay of plants and mud in river flow can inform efforts to restore eroding rivers back to a more stable state. “If you don’t understand what’s driving the river into one state or another, it’s hard to do that well,” says Paola, who coauthored an article about restoring river deltas in the 2011 Annual Review of Marine Science. And since so much of life revolves around rivers today, it’s important to do that well.

"But this has always been true. Life has always congregated around rivers, from the very first emergence of plants and animals onto land. That’s why the early accumulations of mud alongside rivers — and how mud influenced their flow — is nothing to throw dirt on."

Comment: what is key to understanding this evolved process on Earth, is that this is the way God works. Everything is evolved from a beginning: the universe from the Big Bang, the Earth from its beginining, and life from its beginning. dhw has never understood this pattern in God's works, and complains about how God evolved humans, instead of direct creation.