Answer:
365 million years ago
Explanation:
The tetrapods are a super-family which includes all living and extinct vertebrates that have walked and are still walking the Earth, including the mammals, reptilians, dinosaurs, sinapsids, pterodactyls, amphibians, birds. They have evolved from fish-like creatures that were living in the shallows, and over the course of millions of years they were slowly changing and adapting to amphibian life, thus partially aquatic, partially terrestrial. The first proper limbs, at least what is know so far from the fossil records, have emerged with the ichthyostega and acoantostega around 365 million years ago. These two species were able to lift their body above the ground with their limbs, support its weight, and walk on them without dragging their body on the ground. The first transitional limbs can be seen in a species that has been dated to around 375 million years ago, the Tiktaalik, which had had limbs, but still not well developed, and it was only able to stand on them while in shallow water, but on on land.
Convection : Warm air rises and cold air sinks, you have a cycle there :D
You can experience it on the beach shore. Since water has a high heat capacity ( it takes longer to heat up ) and the sand get hot quickly, the air on the shore gets warm and rises. When the air reaches to certain elevation (or meet the temperature of the beach), it gets cooler and sinks, cold air from the beach blown to the shore.
Answer:
The estrogenic activity of BPA represents the major endocrine-disrupting effect of BPA and was revealed in 1993 by a study showing that BPA can be released from polycarbonate flasks during autoclaving. BPA is a weak agonist to estrogen receptor β, but compared to estradiol, its activity is 1000-fold less
Explanation:
