Hazen views earth’s 4.5 billion year history through his unique lens as a mineralogist. He explains how the earth was built from cosmic dust and transformed into continents, oceans, atmosphere, and life. We find out why earth was primed for life and the many ways it could have started. We learn how minerals and living organisms evolved together shaping the future of each other. This very readable book is packed with fascinating insights. Following are my notes.
Hazen puts time in perspective. If on a walk every step equaled 100 years after a mile you would have travelled back 175,000 years, about the time anatomically modern humans first appeared. If you made it twenty miles that day, you would have travelled three million years into the past. At 100 years per step and twenty miles per day how long would it take to travel back to the formation of the earth? Four years! That was 4.5 billion years ago. Here we begin our story as a nebula of dust and gas form our sun and the leftovers accrete to build the planets.
A nascent earth is hit by a smaller sibling, Theia, which disintegrates. Theia’s denser material is drawn into the earth and the lighter material thrust into earth orbit where it coalesces into our moon. At only 15,000 miles up (today it is 239,000 miles) the young moon appeared 16 times larger than today’s sun. A full moon illuminated the night providing more than enough light to read by. But night turned to day quickly with the earth rotating completely every five hours. The moon orbited every 84 hours. What a spectacle it would have been watching the moon go through its phases! Unfortunately the earth’s 10,000 degree molten rock surface buffeted by huge tidal waves would have made observation pretty difficult.
As the earth cooled, chunks solidified based on their chemical composition, denser ones sank and lighter ones floated to the top. Within 100 million years a thin basalt crust formed floating on a molten mantle. The crust was punctuated with mega volcanoes that would build an atmosphere and oceans as carbon dioxide and water from the interior were pumped out. It’s fortunate that the atmosphere was full of carbon dioxide and perhaps methane. For the first 1.5 billion years the sun was 25% less bright than today. Without the greenhouse effect the earth might have quickly become a snowball and life may not have developed.
By 200 million years granite Islands began forming in the basalt magma. Less dense than basalt, granite rose to the top poking above the crust like icebergs do in water. Water filled in over the surrounding basalt crust forming a single mega ocean. In another billion years the granite islands would grow and coalesce into the first super continent. Rain in the carbon dioxide atmosphere fell as carbonic acid breaking down rocks into clays and sending sediments into the ocean. Granite contains lots of quartz so as it weathered nice sandy beaches arose on the shores of the blue ocean. Still the land was stark and gray and devoid of life.
The solar system and earth were rich in the carbon molecules required for life such as amino acids, sugars and lipids. Whether it was the nutrient rich ocean, a hot undersea vent, the sun drenched dense atmosphere or even rocks, somewhere the ingredients combined in the right way and life took off around 4 billion years ago. Predictably the author’s favorite birthplace of life is on rocks. Consider that as much as half of the biomass on earth today is found in the cracks and crevices of rocks penetrating well underground and living off minerals. Hazen uses the chirality (handedness) of amino acids and sugars to make his point. Minerals also have chirality and electric charge, another component of biologic molecules. An article published in Scientific Reports I read on phys.org on 4/4/17 as I wrote this, showed how the zinc clay sauconite can metabolize using the sun’s energy to synthesize new clay particles. Biofilms naturally stick to rocks and clays, which could have provided templates for the first life. Take a planet full of chemically diverse rocks covered with biomolecules; mix, heat and squeeze for five hundred million years. A lot can happen.
Around 2.5 billion years ago, cyanobacteria began producing oxygen as a byproduct of photosynthesis and the first Great Oxidation Event unfolded. The earth’s anoxic atmosphere would be transformed. By 2.2 billion years ago atmospheric oxygen had risen to 1%. This was enough to oxidize the iron in granite, the soil and oceans. The earth’s land surface changed from gray to red. Over the next 1.4 billion years oxygen levels would gradually increase in the atmosphere and the oceans. During that same time plate tectonics would slam granite islands together forming continents, mountains and shallow seas. A cycle of supercontinent creation and destruction would begin.
Oxygen under these conditions would combine with preexisting minerals to create thousands of new minerals. Minerals evolved just as their animate offspring. Free oxygen created by photosynthesis was critical. Two-thirds of known minerals would not have existed on an earth without life including human favorites such as turquoise and malachite. From 15 minerals in the dust of the original nebula the earth now has 4,500 different minerals, our neighboring planets without life at most 1,500.
Between 850 and 750 million years ago the supercontinent Rodina broke up dramatically increasing the shoreline and shallow seas setting the stage for the Second Great Oxidation Event 740 million years ago. Erosion flooded the new algal friendly coastal waters with nutrients. Oxygen producing algae thrived, setting off a cycle of extreme cold and hot periods after a billion years of stability. Reduced carbon dioxide and increased free oxygen disrupted the greenhouse atmosphere and earth turned into a snowball or perhaps just a slush ball. This killed the algae and the oxygen levels declined. Volcanoes pumped carbon dioxide back into the air melting the ice. Minerals subject to extreme weathering released large amounts of manganese, molybdenum and especially phosphorous into coastal waters resulting in massive algal blooms. After 150 million years of repeating cycles oxygen levels reached 20%. This would be the first earth where you could breathe and the first where your skin wouldn’t be quickly torched by UV rays. The degree to which methane was trapped and released as part of these cycles is uncertain, but critical to know in light of our current situation.
These events led to the Cambrian explosion 540 million years ago. New multicellular life forms appeared that evolved into the diverse flora and fauna of today. The ensuing half billion years would be punctuated with calamitous extinctions caused by extreme volcanic activity and asteroid strikes. Each extinction led to new life forms filling vacated niches. 430 million years ago plants and animals conquered the land breaking up rocks and forming more mineral deposits. 300 million years ago in the Third Great Oxidation Event oxygen levels rose to 30% supporting mammoth insects such as dragon flies with two foot wing spans. Much of this was due to carbon sequestration as increasing amounts of biomass were buried, a process which had also contributed to prior atmospheric oxygen increases. The fragments from Rodina collided to form a new supercontinent Pangea. The impact formed the Appalachian mountains then as high as the Himalayas are today. 250 million years ago oxygen levels sank to 15% before eventually recovering to today’s 21%. 175 million years ago Pangea broke up forming the Atlantic Ocean. Plate tectonics would move the fragments (our continents) to their present position.
250 million years from now, the continents will once again collide to form a new supercontinent. Life on earth should last another billion years perhaps two. By that time the sun, continually getting hotter, will evaporate the oceans and extinguish life on earth. We can expect ice ages to recur. We can expect many mega volcanoes and devastating asteroid impacts. Just as in past extinctions many vulnerable life forms will be lost, but others will survive and evolve just as in the past. However, humans along with many other species may not survive long enough to worry about these things. The immediate danger is human driven global warming that is proceeding at an unprecedented rate. We don’t know how it will end. There could be another calamitous extinction and we could well be casualties. But the earth and life will survive, reset and evolve as in the past.
If you got this far I hope you put this well written book on your list. Hazen offers informative discussions of plate tectonics and continent formation. He details theories of the beginning of life. He explains the many ways in which minerals influenced life and in turn life influenced minerals, both working together to shape the environment. He explores the critical role of the abiotic in the ecosystem. We’re all in this together and that includes the minerals.