lifeless layer of basement rock wasn’t just a sliver; the barren layers were miles deep. All of human history—and the entire known history of life on the planet itself—were confined to a thin veneer of crust. If the entire history of Earth were scaled to a year, with its formation on New Year’s Day and the present being December 31, Earth was utterly lifeless until mid-November. Translate this relative timescale into years, and we find that about 4 billion years of the history of our planet was devoid of living things. ToCharles Darwin, the abrupt appearance of life was an “inexplicable mystery.”
The solution to Darwin’s mystery, along with clues to how our modern world emerged, came from a source no one could have ever predicted.
The steelworks of Gary, Indiana, stand like hulkingfossil skeletons of a thriving bygone age. In the 1950s, humming mills fed a burgeoning automotive industry, with plants sprinkled across the Midwest. The need for iron was great, and geologists such asStanley Tyler worked to feed it by studying theiron-ore-containing rocks in the region.
Because the rocks that contain iron tend to be among theoldest rocks around, ore geologists like Tyler focus mostly on the geological basement. As Tyler knew, these rocks were great for industry, lousy forpaleontology.
One afternoon in the mid-1950s, Tyler was studying samples he collected from a deep test pit in northern Michigan. Rock chips from different layers were brought back to his lab in Madison, Wisconsin, where each was ground thin and placed on a slide to observe the fine structure of minerals and grains. Sitting with a checklist and amicroscope, Tyler performed the usual scoring and counting of the color, grain size, and mineral contentthat are the necessary but rote measurements of much geological work.
Elso Barghoorn. (Illustration Credit 5.1)
When Tyler looked at one of the slides under the scope, he saw something familiar yet completely out of place:coal. He knew that coal reflects ancient plant detritus and that most of the coals known at that time were from layers no older than 350 million years, when plant life was abundant. But Tyler also knew the age of his sliver of rock from Michigan. It was almost 2 billion years old. Something was entirely wrong.
Not believing his own eyes, Tyler discreetly passed the rocks to experts. Shuffling from one specialist to the next, the samples eventually ended up in the hands of Elso Barghoorn, a curator of earlyplants at the HarvardMuseum of Comparative Zoology. Scanning the slides under a microscope, Barghoorn immediately confirmed Tyler’s hunch. Tyler had found the earliest life yet known on the planet—coal-formingalgae and other microorganisms.
This answer led to a whole new puzzle. The more Barghoorn looked at Tyler’s slides, the more ancient species he saw. Each sample was brimming with algae spores, filaments, and the remains of thousands of single-celled animals. The basement of rock on our planet wasn’t devoid of life but teeming with it.
Now the “inexplicable mystery” lay not in the missing life but in understanding the plethora of living things that were once hidden from our view. When did life get its start on the planet? What did the earliest living things look like? Because there was a world of questions to ask and creatures to find, a new kindof paleontologist emerged—one whose life’s goal was to recover microscopic fossils from rocks billions of years old.
Hunting for fossils in the first 2 billion years of Earth’s history has special challenges. Rocks of the right type to hold super-ancient fossils are likely to have been eroded away, baked by internal heat, or transformed by various movements of Earth’s crust. Let’s say you actually manage to find ideal rocks. How can you tell that a microscopic bleb or filament was once a living thing and not some mineral or inclusion in the rock? The science of early life is one of constructing multiple lines of
The solution to Darwin’s mystery, along with clues to how our modern world emerged, came from a source no one could have ever predicted.
The steelworks of Gary, Indiana, stand like hulkingfossil skeletons of a thriving bygone age. In the 1950s, humming mills fed a burgeoning automotive industry, with plants sprinkled across the Midwest. The need for iron was great, and geologists such asStanley Tyler worked to feed it by studying theiron-ore-containing rocks in the region.
Because the rocks that contain iron tend to be among theoldest rocks around, ore geologists like Tyler focus mostly on the geological basement. As Tyler knew, these rocks were great for industry, lousy forpaleontology.
One afternoon in the mid-1950s, Tyler was studying samples he collected from a deep test pit in northern Michigan. Rock chips from different layers were brought back to his lab in Madison, Wisconsin, where each was ground thin and placed on a slide to observe the fine structure of minerals and grains. Sitting with a checklist and amicroscope, Tyler performed the usual scoring and counting of the color, grain size, and mineral contentthat are the necessary but rote measurements of much geological work.
Elso Barghoorn. (Illustration Credit 5.1)
When Tyler looked at one of the slides under the scope, he saw something familiar yet completely out of place:coal. He knew that coal reflects ancient plant detritus and that most of the coals known at that time were from layers no older than 350 million years, when plant life was abundant. But Tyler also knew the age of his sliver of rock from Michigan. It was almost 2 billion years old. Something was entirely wrong.
Not believing his own eyes, Tyler discreetly passed the rocks to experts. Shuffling from one specialist to the next, the samples eventually ended up in the hands of Elso Barghoorn, a curator of earlyplants at the HarvardMuseum of Comparative Zoology. Scanning the slides under a microscope, Barghoorn immediately confirmed Tyler’s hunch. Tyler had found the earliest life yet known on the planet—coal-formingalgae and other microorganisms.
This answer led to a whole new puzzle. The more Barghoorn looked at Tyler’s slides, the more ancient species he saw. Each sample was brimming with algae spores, filaments, and the remains of thousands of single-celled animals. The basement of rock on our planet wasn’t devoid of life but teeming with it.
Now the “inexplicable mystery” lay not in the missing life but in understanding the plethora of living things that were once hidden from our view. When did life get its start on the planet? What did the earliest living things look like? Because there was a world of questions to ask and creatures to find, a new kindof paleontologist emerged—one whose life’s goal was to recover microscopic fossils from rocks billions of years old.
Hunting for fossils in the first 2 billion years of Earth’s history has special challenges. Rocks of the right type to hold super-ancient fossils are likely to have been eroded away, baked by internal heat, or transformed by various movements of Earth’s crust. Let’s say you actually manage to find ideal rocks. How can you tell that a microscopic bleb or filament was once a living thing and not some mineral or inclusion in the rock? The science of early life is one of constructing multiple lines of
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