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How Earth's earliest trees grew

A Devonian Xinicaulis tree trunk fossil from northwest China. Photo via PNAS

Scientists have used fossils to discern how some of Earth's earliest trees called cladoxylopsids, which helped to jumpstart the planet's earliest forests about 374 million years ago, actually managed to grow, per the Los Angeles Times. Cladoxylopsids have no living modern ancestors and are believed to be most closely related to ferns.

Why it matters: The discovery helps us to better understand how some of the key inhabitants of our planet's first forests managed to survive. In turn, knowing more about cladoxylopsids could help shed light on how early plants helped to make Earth's climate habitable for the first animals by reducing the planet's carbon dioxide levels.

How modern trees grow: Trees today grow outward from the center in rings by adding xylem, which are woody fibers that carry water up the trunk. From this growth process, most species of trees generally have a uniform width.

How cladoxylopsids grew: The ancient trees' xylem grew in their outer trunks in tiny strands that were connected by even smaller strands — all centered around a hollow core. When cladoxylopsids grew, the tiny strands on the outside of the tree would continuously tear themselves apart before entering into a stage of repair. As a result, cladoxylopsids had collapsed trunks that were significantly fatter on the bottom.

What's next: Scientists want to try to understand how cladoxylopsids took in carbon, which would teach us more about Earth's early climate changes just as biology began to diversify.

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