How life's forms modify and evolve the Earth (Introduction)

by David Turell , Friday, September 01, 2023, 19:57 (239 days ago)

Noted early on by Darwin:

https://aeon.co/essays/the-insight-of-darwins-work-on-corals-worms-and-co-evolution?utm...

"if Earth had never come alive, it would be a profoundly different world. Conversely: the planet of today has, to a remarkable extent, been made what it is by the activities of lifeforms. Over the course of the planet’s long history, a history that extends back more than 4.5 billion years, lifeforms have shaped the rocks, the water, the air, even the colour of the sky. A Never-Life Earth would not even have as many different kinds of minerals.

" The central observation...is that, over time, lifeforms have profoundly altered the fabric of this planet, and this, in turn, has altered the circumstances in which lifeforms evolve.

***

"Darwin’s first scientific monograph and his last – the two bookends of his thoughts, so to speak – were both about how animals have, over vast spans of time, transformed the landscape.

"These two works of biogeology – one on coral reefs, the other on earthworms – were, as far as I know, the first detailed studies of the subject ever published. On casual inspection, they appear to be unrelated undertakings, just part of Darwin’s long and eclectic list of interests, along with barnacles, orchids, carnivorous plants,...and other animals, the volcanoes of South America, and so on...The Structure and Distribution of Coral Reefs appeared in 1842, while his book on earthworms, The Formation of Vegetable Mould, Through the Action of Worms, with Observations on Their Habits, came out in 1881, about six months before he died. (Vegetable mould is what you and I would call topsoil.)

***

"Darwin suggested instead that atolls form on the slopes of volcanoes that are slowly sinking. Here’s a brief sketch of the idea. A volcano erupts and builds an island in the middle of the ocean. Coral animals settle on its slopes, luxuriating in the warm, shallow, sunlit waters, and begin building the limestone skeletons that, together, will form a reef. If the seafloor then begins to subside, the volcano will gradually sink back beneath the waves – but the corals will continue to grow upwards, so as to remain in the shallows. As long as the volcano doesn’t sink too fast, the corals can keep pace with its descent.

***

"Eventually, the volcano may vanish far beneath the waves, leaving just the coral as a marker of its existence. Each atoll is a requiem for a volcano. Or, as Darwin wrote – ‘a monument over an island now lost’.

"His argument makes a clear prediction: somewhere beneath each atoll, beneath these immense piles of life-built rock, these mountains of limestone, you will find the remnants of a volcano.

***

"In the 1940s and ’50s, the United States government tested dozens of nuclear weapons in the Marshall Islands, a cluster of atolls that lie in a remote part of the Pacific a little to the north of the equator. This brought a host of scientists – geologists, biologists, oceanographers – to study the area. In 1952, a team of geologists drilled deep into Enewetak Atoll. At 1,283 metres (4,208 feet), they struck basalt. Volcanic rock. Darwin was right.

***

"his book on earthworms, The Formation of Vegetable Mould, Through the Action of Worms, with Observations on Their Habits, came out in 1881, about six months before he died...At the time, the book was wildly popular, selling 3,500 copies within the first month. Today, though, it is little read, and often dismissed as the eccentric afterthought of a great man whose life was drawing to a close.

***

"His uncle speculated that this was due to the activities of earthworms. As they burrowed through the soil, the worms were, his uncle suggested, acting as slow-motion ploughs. Altogether, the observations were so interesting that William Buckland, an eminent geologist of the day, suggested that Darwin had identified ‘a new Geological Power’.

***

"Earthworms burrow through soil by eating it; they also nibble on organic matter such as dead leaves. To defecate, they generally come to the surface, where they eject, as Darwin put it, ‘little intestine-shaped heaps’ known as castings. On the basis of his conversations with his uncle, Darwin suspected the worms of tilling the soil, bringing fine particles from deep in the ground up to the surface.

***

"Taking his results together, Darwin showed that earthworms have several important effects. The animals do not just mix the soil by bringing deeper material up to the surface. By munching on fallen leaves, and by pulling those leaves down into their burrows, they also create new soil and enrich it with a nutritious compost.

***

" Darwin: "The plough is one of the most ancient and most valuable of man’s inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earthworms."

"Worms might appear insignificant, but because there are so many of them, little by little, they sculpt the contours of the world.

***

"At the end of his book, he remarks: ‘It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.’ In this, however, he profoundly underestimated the scale of the changes wrought by other lifeforms."

See life forms II.