History of Earth predicts its future

My interest in the native plant movement began about 25 years ago when my neighborhood park was designated as a “natural area” by San Francisco’s Recreation and Park Department.  My park was only one of 33 parks in San Francisco that were designated as a “natural area.” 

What did it mean to be a “natural area?”  As I studied the plans, my reaction was primarily to the proposed destruction of non-native plants and trees.  Later I realized that the eradication of non-native plants and trees would be accomplished with herbicides. 

Stern Grove Park in San Francisco was my neighborhood park where I began my long journey to understand why anyone would want to destroy trees in a treeless neighborhood. 

How could the creation of native plant gardens justify the destruction of our urban forest using herbicides?  I have spent the last 25 years trying to answer that question.  There are many useful lines of inquiry in the search for the answer, but the approach that has been most helpful to my understanding of the futility of the undertaking has been the study of the physical and biological forces that created Earth and its inhabitants.  Today, I will take you on an abbreviated journey of the past 4.6 billion years of events on Earth that have resulted in present-day nature, drawing from A Brief History of Earth by Andrew Knoll, Professor of Natural History at Harvard University. (1)

Gravity “created” the Earth

“Gravity is the architect of our universe.”  Gravity is the attraction of objects to one another in proportion to their mass and proximity that over billions of years accumulated the elements dispersed in Earth’s universe.  As these dispersed objects coalesced into stars, planets, moons, and asteroids, Earth was formed about 4.6 billion years ago.

Cross-section of Earth. Source: USGS

“Earth is a rocky ball.”  Its inner core is solid, composed mostly of iron.  Earth’s molten outer core moves by convection as hotter, denser material near the base rises and cooler, less dense matter toward the top sinks.  This circular motion generates electrical current that creates the Earth’s magnetic field.  The mantle is composed of the molten magma that emerges on the surface crust of Earth where tectonic plates are separating and when volcanoes erupt where tectonic plates submerge into the mantle. The crust of Earth that is visible to us is only 1% of Earth’s mass.

Physical Earth

Simplified map of Earth’s principal tectonic plates, which were mapped in the second half of the 20th century (red arrows indicate direction of movement at plate boundaries).  Source:  USGS

The crust of Earth is composed of plates that are moved on the surface of the Earth by the convection current of the mantle.  Some of the plates are moving away from one another where they meet.  As the plates separate, molten magma from the mantle is pushed through the crust, forming new crust.  The North American and Eurasian plates are moving apart in the middle of the Atlantic Ocean at the rate of about 1 inch per year. 

Since the Earth is not getting bigger, the expanding crust collides with adjacent plates.  In some places, the collision of the plates pushes up the crust into mountain ranges.  The Himalayan mountain range is the result of the collision of the Indo-Australian and the Eurasian Plates, a process that continues today.

Map of subducted slabs, contoured by depth, for most active subduction zones around the globe. Source:  USGS

In other places, the expanding crust is pushed below the adjacent plate in subduction zones, where the crust dives below the crust into the mantle.  Earthquakes are common in subduction zones and the subducting plate triggers volcanic eruptions in the overriding plate.  Earthquakes are also common where adjacent plates are grinding against one another in opposite directions, as is the case on the coast of California.

Pangea super-continent

The movement of tectonic plates has assembled and reassembled the Earth’s continents many times. The entire history of the configuration of continents is not known to us because of the cycle of the crust emerging from the mantle only to return to the mantle about 180 million years later.  We know that all continents were fused into a single continent, named Pangea, about 350 million years ago and began to break up 200 million years ago.  Much of life as we know it evolved on Earth while the continents were fused, which is one of the reasons why all life on Earth is related.  Geographic isolation of species results in more biodiversity as genetic drift and different environments result in greater speciation.  Geologists believe such continental mergers are likely in the distant future.  

Earth’s oceans and atmosphere were formed within the first 100 million years of its birth.  Continents were visible above oceans, but small compared to their present size.  The absence of oxygen in the air at that early stage was the most significant difference between present and early Earth.

Biological Earth

Life, as presently defined, requires growth and reproduction, metabolism, and evolution. (I say, “presently defined” because debate continues about defining viruses as life since they do not meet all criteria.)  The chemical components required to perform the functions of life and the natural processes to combine them (such as heat and lightning) were available on Earth for millions of years before they combined to perform the functions of life.  Precisely how and when that happened on Earth is studied intensely, but not conclusively known, although Professor Knoll describes theoretical possibilities. 

The geological record suggests that “Earth has been a biological planet for most of its long history.” Microbes may have been living on Earth 4 billion years ago.  Climate on Earth was warm at that time for the same reason the climate is warming today.  The atmosphere was composed primarily of carbon dioxide (the greenhouse gas that traps heat on the surface of the Earth) and nitrogen:  “…life emerged on an Earth barely recognizable to the modern eye—lots of water and not much land, lots of carbon dioxide but little or no oxygen…”

Oxygen Earth

Phylogenetic tree of life based on Carl Woese et al. rRNA analysis. The vertical line at bottom represents the last universal common ancestor.

Two of the three domains of life were capable of living without oxygen:  archaea and bacteria.  Archaea are single-cells without nuclei.  We are all too familiar with bacteria, as they are as much a part of our bodies as our own cells.  Oxygen was the prerequisite for the evolution of the third domain of life, eukarya.  The kingdoms of eukarya most familiar to us are plants, animals, and fungi. 

Oxygen arrived on Earth when early life forms evolved the ability to photosynthesize, the process by which plants (and some other organisms) use sunlight to synthesize food from carbon dioxide and water, generating oxygen as a byproduct.  This transition occurred about 2.4 billion years ago, as measured by the absence of iron on the seafloor after that time. 

Photosynthesis alone could not have accomplished the transformation of Earth’s atmosphere to the balance of carbon dioxide and oxygen needed to support complex life on our planet because photosynthesis also requires nutrients as well as sunlight and water.  Phosphorous weathers from rocks, a process that was initially limited by the small amount of land above sea level.  As the planet matured, more land emerged from the sea, making more phosphorous available to photosynthesizing organisms.  Photosynthesis was also enhanced when some bacteria and archaea evolved the ability to convert nitrogen gas into biologically usable molecules, a process called nitrogen-fixing.  Many plants in the legume family are capable of nitrogen-fixing today.

Extinctions of the past predict extinctions of the future

There have been five major extinction events in the past 500 million years that changed the course of evolution of life on Earth and at least 20 mass extinctions in total (2).  The first representatives of all modern animal phyla (a taxonomic classification between kingdom and class) evolved during the Cambrian Period (541-486 million years ago).  All extinction events were associated with radical changes in the climate.  Many of the changes in the climate were caused by changes in the balance of carbon dioxide and oxygen in the atmosphere.  All these catastrophic events were natural events, not caused by the activities of humans because they all occurred long before the advent of human evolution. 

The third and biggest extinction event occurred 252 million years ago at the end of the Permian geologic period, when more than 90% of marine animals and 70% of terrestrial species disappeared.  At that time, continents were fused into the single supercontinent of Pangea.  The extinction of most life on Earth was caused by the sudden and catastrophic change in the atmosphere–and therefore the climate–by an episode of volcanism in Siberia “a million times greater than any volcanism ever witnessed by humans” or our primate ancestors.  Gases emitted by volcanism at the end of the Permian period rapidly increased the carbon dioxide content of the atmosphere and oceans by several times greater than before that event.  “It would take 10 million years for life to reassemble into something approaching the complexity of the ecosystems that preceded it. The world that emerged from the volcanic dust was unlike anything that came before.” (2) The current increase of carbon dioxide in the atmosphere caused by the burning of fossil fuels by human activities is comparable to this event and is expected to cause the sixth great extinction on Earth.  

The fifth and most recent massive extinction event occurred 66 million years ago, bringing 170 million years of dinosaur evolution to an abrupt end. The entire environment of the planet was radically and suddenly altered by the impact of an asteroid 7 miles in diameter that landed on what is now the Yucatan peninsula in Mexico.  The impact engulfed Earth in a dust cloud that precipitated the equivalent of a nuclear winterkilling most vegetation and animals adapted to a much warmer climate.  As with all massive extinctions, it took millions of years for plants and animals to slowly evolve adaptations to the new environment.  Dinosaurs did not evolve again, a reminder that evolution does not necessarily repeat itself (although birds evolved from dinosaurs).  Although there were small mammals during the dinosaur age, the disappearance of dinosaurs and corresponding changes in the climate introduced the age of mammals, including the human lineage about 300,000 years ago.  When multiple animal groups disappear it creates opportunities by reducing competition between groups.

What can we learn from the history of Earth?

If a native plant advocate were reading this abbreviated history of Earth, these are the lessons I would hope they might learn from it:


  1. Andrew H. Knoll, A Brief History of Earth, 2021.  All quotes in this article are from this excellent book unless otherwise indicated.
  2. Elsa Panciroli, Beasts Before Us: The Untold Story of Mammal Origins and Evolution, Bloomsbury Sigma, 2021.

A glimpse of Iceland

“Consistently rated the most peaceable of all countries in the world by the global peace index, Iceland has reduced its military expenditure to zero, has no armed forces, and has reduced the inequality gap between rich and poor.” – Scilla Elworthy

We were traveling when the pandemic began in 2020.  We felt lucky to get home on one of the last flights to leave Buenos Aires on March 15, 2020, before Argentina locked down.  The first stay-at-home order in the Bay Area was announced a few hours after we arrived home on March 16th.  Since then it was never clear when we would be able to travel again.  Frankly, it still isn’t, but we signed onto a trip to Iceland in July anyway because it was the first trip that looked relatively safe and I guess it was.  We were allowed to visit 3 ports before one positive Covid test on our ship cancelled visits to the remaining 3 ports. 

Iceland is one of the most geologically interesting places on the planet.  It is equally interesting culturally because it is a highly functioning society and one of the oldest democracies in the world.  I’ll share a few tidbits about what we learned in Iceland because some are relevant to my interest in natural history.

A New Land

Geologically, biologically, and culturally, Iceland is a new landIt was created about 18 million years ago by molten rock arising from the great rift of the North American and European tectonic plates.  Unlike the junctures of most of the tectonic plates that form the surface layer of Earth, the North American and European tectonic plates are separating, which creates an escape route for the molten material below the surface of the Earth.  This rift is thought to have separated the fused, singular continent of Pangea, creating the Atlantic Ocean.  This separation of the continents began some 180 million years ago, putting the relative youth of Iceland into time perspective.

red triangles are active volcanoes

Iceland remains a geologic hot spot where volcanic eruptions, lava flows, and earthquakes are frequent occurrences.  Geysers, hot springs, and fumaroles are constant reminders that Iceland sits on a rift in the Earth’s crust that provides immediate access to the Earth’s molten interior. Icelanders heat their homes with geothermal hot water and their electricity is generated hydrologically. Their air is cleaner because they are burning little fossil fuel.

Geothermal geyser in Iceland
Geothermal hot spring in Iceland
One of many huge waterfalls in Iceland

Land created by volcanic eruptions is composed of barren rock. Turning rock into soil is a slow process, typically taking thousands of years.  Every new volcanic eruption on Iceland adds more barren rock.  A series of volcanic eruptions that began in 1963 created the island of Surtsey on the southern coast of Iceland.  It was immediately designated as a nature reserve that prohibits all but scientists from visiting.  It is therefore a laboratory to study the lengthy process of colonizing barren rock with plants and animals.

Surtsey, 1963. VisitWestmanIslands.com

The first terrestrial plant was found on Surtsey in 1965, while the eruption was still active. Mosses were found in 1967 and lichens in 1970.  Mosses and lichens now cover much of the island.  Although 20 plant species were observed over the first 20 years, only 10 species became established in the nutrient-poor soil. 

Soil conditions began to improve when birds began nesting on the island.  By 2008, 69 plant species had been found on Surtsey, of which 30 species were established.  More species continue to arrive at the rate of 2-5 species per year, but Surtsey’s plant life is a small fraction of the 490 plant species found on mainland Iceland. 

Scientists give the birds on Surtsey credit for much of its flora:  “Birds use the plants for nesting material, but also continue to assist in the spreading of seeds, and fertilize the soil with their guano. Birds first began nesting on Surtsey three years after the eruptions ended…Twelve species are now regularly found on the island.”  This is a reminder that humans are not the sole dispersers of plants to new locations.

Insects were first detected on Surtsey in 1964.  “The original arrivals were flying insects, carried to the island by winds and their own power. Some were believed to have been blown across from as far away as mainland Europe. Later insect life arrived on floating driftwood, and both live animals and carcasses washed up on the island. When a large, grass-covered tussock was washed ashore in 1974, scientists took half of it for analysis and discovered 663 land invertebrates, mostly mites and springtails, the great majority of which had survived the crossing. The establishment of insect life provided some food for birds, and birds in turn helped many species to become established on the island.”  Wind, storms, ocean currents are other methods of natural dispersal of species to new locations

Although we saw many cosmopolitan plant species on Iceland that are found all over the world, such as dandelions and clover, only one introduced plant seemed to be controversial.  Lupine was introduced to Iceland in about 1970 to deal with soil erosion in coastal areas.  It has spread far beyond where it was introduced and has earned a reputation as an “invader.”  That reputation can be the beginning of a poisonous eradication campaign.

Lupine blooming in Iceland. Our cruise ship can be seen in the distance.

However, although we saw lupine wherever we went, most of our guides and lecturers were more positive than negative about it.  They acknowledged that some people don’t like the spreading lupine, but they explained that lupine is a nitrogen-fixing plant that builds soil in a place that is dominated by rocky, nutrient-poor soil.  Based on our limited experience in Iceland it seems that lupine is selling itself to the people of Iceland as a non-native plant that brings more benefits than problems. 


Update:  Adalsteinn Sigurgeirsson is the Deputy director of the Icelandic Forest Service.  He has given his permission to publish his Facebook comment to this article: “I fully agree with you, in your analysis of the discourse in Iceland on the Nootka lupin. The general public favors the plant, as it is able to “invade” derelict soils on eroded land and replenish the nitrogen stocks in the soils. However, as elsewhere in Western societies, “people who favor native plants are invading our local, state, and national governments, spending taxpayer dollars on the destruction of our environment.” (http://lazycompost.com/the-invasiveness-of-native…/…).

“Iceland’s history since settlement in the 9th century is one of nearly wholesale deforestation, soil erosion and ecosystem destruction. A likely underlying reason for this state of affairs is the lack of nitrogen-fixing plants in our native flora (lack of biodiversity in general, on a remote island in the N-Atlantic). The few native nitrogen-fixers have been introduced since settlement and these can only grow if fenced off from the omnipresent, free-roaming TGBs (tree-gobbling bastards, i.e. sheep). Icelandic volcanic soils are rich in all plant nutrients, save nitrogen.” https://www.skogur.is/…/history-of-forests-in-iceland


A new culture and an old democracy

Iceland was inhabited by humans about 1,100 years ago, one of the last patches of land on Earth to be colonized by humans.  Our hominoid species, Homo sapiens evolved in Africa over 300,000 years ago and began migrating out of Africa shortly after.  Humans occupied Australia, another island nation, about 60,000 years ago and one of the most recent human migrations occurred about 13,000 years ago to North America.  In other words, Iceland is one the last places on Earth occupied by humans.

This is the narrow canyon created by the rift between the North American and European tectonic plates, where the Iceland parliament, called the Althing, first met in 930 A.D.

Shortly after being colonized by Vikings, Iceland formed one of the first parliamentary bodies in the world.  The first meeting of the Althing was in 930.  Ironically, it occurred in one of the most geologically interesting places in Iceland where the rift separating the North American and European tectonic plates forms a narrow canyon. The early settlers had no way of knowing they were meeting in a place of great geologic importance.  They selected it because the towering walls of the canyon provided shelter in an extreme climate for their annual meeting that required a temporary encampment of chieftains coming from all over Iceland. 

A highly functioning society

The population of Iceland is less than 360,000, less than the population of my hometown, Oakland, where about 425,000 people live and actively participate in a complex, diverse society where democratic decisions are made, but not without heated debate and frequent conflict.  Based on my experiences at home, I admire Icelandic culture. 

The unique manner in which Iceland dealt with the economic collapse of 2008 that caused financial hardship all over the world is one example of how problems are solved in Iceland.  Bankers in Iceland engaged in the same risky borrowing and lending that caused the financial collapse in the US and the government was complicit because it did not enforce the laws that could have prevented some of those risks.  However, Iceland is the only country that reacted to that collapse by replacing the government, closing the banks, prosecuting and jailing the bankers who broke the laws.  Once again, Iceland’s economy is strong despite 18 months of collapse of their tourist industry, which is second only to the fishing industry in creating jobs in Iceland. 

Cemetery in Iceland

On the last day of our visit to Iceland we had our only opportunity to wander freely in Reykjavik before boarding our plane.  We were able to visit a cemetery close to the museum that was functioning as our waiting room before our flight.  Early on a Saturday morning a large group of people was visiting the grave of family or friend.  It seemed to be a festive occasion for them and their mood was consistent with the cemetery itself.  Every gravesite was decorated with a small garden of blooming annual plants that must be planted every year after their extreme winters.  Every gravesite said that families and ancestors are respected and loved.  We are regular visitors to a historical cemetery in our neighborhood in Oakland.  Although it is well tended by cemetery staff, there is little evidence of the active participation by the families of those buried there. 

Gravesite in Iceland

One of the gravestones in the Icelandic cemetery was inscribed with “I did it my way,” a clue to the influence of America in Iceland where we have had a strategically important military presence since World War II.  Iceland is the midpoint on the flyway between Europe and North America and therefore crucially important militarily. 

 Thank you, Iceland, for graciously hosting our first voyage back into the world.