50 mllion years ago
By 400 million years ago, as the first jawed fishes ambled ashore and at the time of the earliest wingless insects, vascular plants were already thriving. A crucial challenge of the new land environment was water shortage. One solution was the development of seeds. The durable seed permits the plant embryo to wait for the best moment to develop. The invention can be appreciated by conjuring up a comparable structure for mammals. Imagine if human zygotes were wrapped in protective time-release capsules that were activated only by a booming peacetime economy. How convenient it would be for a distracted young woman it she could collect and store her babies-to-be, germinating them only after receiving her college diploma, buying her house and, in general, securing her future. Seeds permitted embryonic plants to wait and silently monitor the environment until favorable conditions arose. The first forests contained giant "seed ferns." These were trees that looked like supersized ferns but which, unlike ferns, produced seeds. For over a hundred million years, from 345 to 225 million years ago, durin g the time of the evolution of winged insects, torpedo-shaped squids, and dinosuars the seed ferns grew in lush, tropical splendor. The first mammals, warm-blooded egg-layers and small marsupials, date to the period of the first flowers, evolving some 125 million years ago. By the early Cenzoic Era, mammals had come into their own, wandering toward polar caps, climbing trees and the highest mountains. Learn More
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