evolution: early eukaryote molecular evidence (Introduction)

by David Turell , Monday, October 23, 2023, 22:22 (395 days ago) @ David Turell

Finding ancient sterols in rocks:

https://www.quantamagazine.org/fossilized-molecules-reveal-a-lost-world-of-ancient-life...

"Limited fossil data shows that their first ancestor appeared at least 1.6 billion years ago. Yet other telltale proofs of their existence are missing. Eukaryotes should produce and leave behind certain distinctive molecules, but fossilized versions of those molecules don’t show up in the rock record until 800 million years ago. This unexplained 800-million-year gap in early eukaryotic history, a crucial period when the last common ancestor of all of today’s complex life first arose, has shrouded the story of early life in mystery.

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"A recent study published in Nature offers an alternative explanation: Scientists may have been searching for the wrong fossilized molecules this entire time. When the study authors looked for more primitive versions of the chemicals others had been searching for, they discovered them in abundance — revealing what they described as “a lost world” of eukaryotes that lived 800 million to at least 1.6 billion years ago.

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"When the fossil record is underwhelming, scientists have other ways to estimate when different species branched off from one another in the evolutionary tree. Primary among those tools are molecular clocks: stretches of DNA that mutate at a constant rate, allowing scientists to estimate the passage of time. According to molecular clocks, the last common ancestor of modern eukaryotes, which belonged to a diverse collection of organisms known as the crown group, first emerged at least 1.2 billion years ago.

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"Organic material decays at different rates, and some parts of eukaryotes preserve in rock better than others. Tissues dissolve first. DNA might stick around for longer, but not too long: The oldest DNA ever found is around 2 million years old. Fat molecules, however, can potentially survive for billions of years.

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"Eukaryotes create vast quantities of fat molecules known as sterols, a type of steroid that’s a critical component of cell membranes. Since the presence of a cell membrane is indicative of eukaryotes, and fat molecules tend to persist in rock, sterols have become the go-to molecular fossil for the group.

"Modern eukaryotes run on three major sterol families: cholesterol in animals, phytosterols in plants and ergosterol in fungi and some protists. Their synthesis starts with a linear molecule, which the cell molds into four rings so that the resulting shape fits perfectly into a membrane, Brocks said. That process has many stages: It takes another eight enzymatic steps for animal cells to make cholesterol, while plant cells require another 11 enzymatic steps to make a phytosterol.

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"Some samples were filled to the brim with protosteroids. They found the molecules in rocks dating from 800 million to 1.6 billion years ago. It seemed that not only were ancient eukaryotes present for some 800 million years before modern eukaryotes took off, but they were abundant.

"The researchers could even recognize the eukaryotes’ evolutionary process as their steroids became more complex. In 1.3-billion-year-old rocks, for example, they found an intermediate molecule that was more advanced than the 1.6-billion-year-old protosteroids, but not as advanced as modern steroids.

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"The molecular findings, put together with genetic and fossil data, reveal the clearest picture yet of early eukaryotic dynamics from around 1 billion years ago during the mysterious mid-Proterozoic era, experts said. Based on Brocks and Nettersheim’s evidence, stem- and crown-group eukaryotes likely lived together for hundreds of millions of years and probably competed with each other during a period that geologists call the Boring Billion for its slow biological evolution.

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"Cohen, the Williams College paleontologist, agrees. The interpretation that these molecules were made by eukaryotes “is consistent with every other line of evidence,” she said — from the fossil record to molecular clock analyses. “I’m not as worried” about that possibility, she said."

Comment: much of evolution involves molecular transformations which then translates into morphologic changes and new biochemical processes. dhw wonders why God used this slow, laborious process. I don't know why. but God obviously knew what He was doing.