Archaeopteris, the first modern trees

Archaeopteris was a tree of the Late Devonian, from about 385 to 360 million years ago, that grew up to 20 to 30 metres tall with a trunk close to 40 centimetres across in the largest fossils. It had true wood made by a cambium layer, like modern trees, branches that carried flat fern-like leaves and a deep, spreading root system. It reproduced by spores rather than seeds. The foliage was named Archaeopteris by John William Dawson in 1871, and in 1960 Charles Beck at the University of Michigan showed that the large wood called Callixylon belonged to the same plant.¹³

Archaeopteris forests spread from the tropics to high latitudes. Earlier trees such as Wattieza of the Gilboa forest in New York had no true wood and shallow roots. Archaeopteris roots broke up rock and built thicker soils, and the leaf litter and branches changed streams, because fallen wood now fed rivers and the sea. Some researchers, notably Thomas Algeo and Stephen Scheckler in 1998, proposed that deeper weathering pulled carbon dioxide from the air and fed nutrients into the sea, helping trigger algal blooms and low oxygen that contributed to the Late Devonian extinctions. That link remains a hypothesis.²³