Otherlands' Tour of Microbes Through Prehistory

by Janie
 

Otherlands

A Journey Through Earth's Extinct Worlds

By Thomas Halliday

 

"It is the crucial paradox at the heart of pal­eon­tology that prac­tically all our infor­ma­tion about life comes only from death." This line from Thomas Halliday's Otherlands, of course, refers to the fos­sil record. So, it stands to reason that the en­tire field of pal­eon­tology is con­tin­gent upon mic­robes: whether microbes can or cannot access and com­pletely decom­pose a dead organ­ism. It's the lat­ter path that allows a creature's record of exis­tence to per­sist through time and to be hap­pily dis­cov­ered by pal­eon­tolo­gists.
 

Fig. 1. American book cover. Source.

Drawing upon the fos­sil record and pal­eon­tolog­ical strata­gems, Thomas Halliday con­jures up lush and sweep­ing tab­leaus of ancient eco­sys­tems in his book, Otherlands, begin­ning with the Pleistocene of 20,000 years past and work­ing back­wards through 550 mil­lion years to ar­rive in the wat­ery Ediacaran. Each chap­ter is a win­dow into one geol­ogic era or epoch. For each time per­iod, Halliday has picked a parti­cular rep­resen­tative fos­sil site to breathe life into, and from such sur­viv­ing evi­dence he deduces the move­ment of that period's flora and fauna, climate, weather pat­terns, cyc­ling of water and soil and carbon. This rev­erse chrono­log­ical por­trait­ure of the shif­ting land­scapes – lakes drain­ing and refil­ling, conti­nents push­ing up against each other and buck­ling into moun­tain ranges, new plants and ani­mals rising and fading – reminded me of a sculp­tor at work with clay in a stop-motion film, effort­lessly grace­ful to the on­looker. All of Earth's con­tours move in fast-rewind in these pages.
 

This being Small Things Considered, I read with an eye out for the microbes. Through Otherlands' chron­icling of Earth's past epochs (large things consid­ered…), we can glean a bird's-eye view of microb­ial activ­ity on Earth.
 

But first, patience – meta­zoans domi­nate the first half of the book. It opens with the Pleistocene epoch, in which perma­frost gives way to bogs and melt­water rivers and taiga forests, roamed both by mega­fauna like mam­moths and mas­sive bears and smal­ler life­forms like horses, birds, and insects (and the prehis­toric humans res­pon­sible for the Lascaux cave paint­ings!). We are then wound back 4 mil­lion years to the Pliocene, witnes­sing the rise of C₄ plants equip­ped with RuBisCO and of the early hom­inin Australopithecus. The Miocene from 5 mil­lion years ago sees the genesis of the Mediterranean basin, its crea­tures mar­ked by dwar­fism and gigan­tism; the Oligocene (32 mya) sees the pre­pond­erance of grasses; the Eocene (41 mya) the giant pen­guins and the sudden warm­ing of the planet by carbon diox­ide and meth­ane; the Paleocene (66 mya) the resur­gence of life after the aster­oid impact at Chicxulub. Before that famed extin­ction event, there is the Cretaceous (125 mya), with thero­pods like the feath­ery Velociraptor of fame and the rise of the flower­ing angio­sperms; the Jurassic (155 mya), with Earth's first birds and a mas­sive reef of glass sea sponges three times the size of today’s Great Barrier Reef; the Triassic (225 mya), with land­lubber dino­saurs and air­borne ptero­saurs and sea-dwelling plesio­saurs; and the Permian (253), in which life roamed atop Pangaea.
 

Fig. 2. An example of fossilized stro­m­a­t­o­lites. Source.

It's in the remain­der of the book that microbes take the lime­light. First stop here is the Carboniferous period (308 mya), with forests turn­ing into peat turn­ing into coal, a time when lignin in wood is novel enough that it is not yet easily broken down by microbes. In the Devonian (407 mya), fish evolve legs and venture onto land, where there are hot ponds inhab­ited by alkali­thermo­philes and cyano­bac­teria. Here, fungi enter into part­ner­ships: with plants, to form the first mycor­rhizae, and with cyano­bac­teria, to form the first lichens. In the Silurian (435 mya) oceans teem­ing with fish, microbes flourish ar­ound hydro­thermal vents, also sym­biot­ically associ­ating with tube worms (as covered in prev­ious STC posts, here and here), and the bac­teria coat­ing sea­floor basalt fix large quan­tities of carbon as they still do today. In the Ordovician (444 mya), strange invert­ebrates swim through the seas and gla­ciers reshape the Earth, while algal blooms lead to con­stant marine snow that falls to the sea floor and nour­ishes the sulfur bac­teria. In the Cambrian seas (520 mya), there are a lot of multi­cellu­lar firsts: the first verte­brates, the first eyes, the first pred­ators, the first hard body parts wrought from cal­cium car­bonate, and the first known crea­ture to brood and protect its eggs. Finally, the Ediacaran (a whop­ping 550 mya) sees a defros­ting Snowball Earth whose seas are ruled by microbes and ses­sile crea­tures. Cyano­bac­teria thrive in these oceans – plenti­ful prey for newly multi­cellu­lar algae – and the sea­bed is coated by microb­ial mats and stromat­olites. And life even further back? "In the end­less out­back of early Earth his­tory… are only microbes."
 

I loved this book. What is unfam­iliar is made know­able, and what is already fami­liar about life on Earth is made excit­ingly novel through views from un­usual angles. It gave me a renewed ap­preci­ation for microbes as Earth's engin­eers since the dawn of life. As I read this rewind of Earth's eras and epochs, I recal­led prev­ious STC posts, and I won­dered: With all the insect diver­sity of the Cretaceous, how many of those insects were asso­ciated with Wolbachia, and did microbes play protec­tive roles for their eggs as they do today? Did the spring­tails jump­ing about in the Devonian have such inter­twined rela­tion­ships with Streptomyces and geo­smin? About those nema­tode worms that parasi­tized Devonian plants – what of microb­ial compan­ions in their gut? Could fluc­tua­tions in pop­ula­tions of ice-nucleating bac­teria have affec­ted global cycles of freez­ing and thaw­ing? And so on.
 

The writ­ing itself is also beaut­iful. With the sub­ject matter handled so thought­fully not only at the level of metic­ulously detailed facts, as is already expec­ted of science books, but even down to the con­struc­tion of sen­tences, it's hard not to share the author's ten­der awe of Earth and its life­forms. It is evoca­tive writing. At times it's play­ful, even punny (a per­sonal fav­orite phrase: "before mol­luscs took that mantle").
 

My only complaint: Halliday repeat­edly attrib­utes the ori­gins of life on Earth to deep-sea alka­line vents. Of course, the compet­ing argu­ment for hot land-based ponds as the cradles of first life is compel­ling, and evi­dence in favor of this theory is gain­ing mass and trac­tion. This alter­nate theory is not men­tioned.
 

Regard­less, Otherlands is a delight­ful tour-like read. What a trib­ute to Earth's life in all its past, pres­ent, and future forms. For those exper­ien­cing wander­lust but unable to travel, here is the sol­ution.