海水、大气化学演化对动物起源和进化方向的制约

动物的起源主要依赖于氨基酸等有机小分子在海水中能否进行脱水缩合反应而生成生物高分子，后者则依赖于海水pH值升高和大气CO2浓度降低的历史演化进程。有机小分子只有在海水pH值演化到近中性，即寒或纪时彼此才能发生脱水缩合反应而合成生物高分子。只有大气CO2分压降到1000Pa以下，即泥盆纪以后，陆地上才能出现稳定的土壤层和植物，动物也才能从海洋扩展到陆地。随后大气CO2浓度继续降低导致了气温下降和植物生长率的衰减，促使动物进一步演化。

CONSTRAINTS OF ATMOSPHERE AND SEAWATER EVOLUTION ON THE ORIGIN AND PROGRESS OF ANIMALS

The origin of animals is dependent mainly on" dehydration- condensation reaction" between small organic molecules as amino acids enter into organic high molecules as protein, ribonucleic acid, polysaccharidsand so on in seawater. Research showed that the" dehydration- condnsation reaction"is dependent on t thecourse of pH-evolution of seawater and Pco2-falling in the atmosphere. When the pH of seawater went upto near-neutral pH, i. e., ouly up to Cambrian, the" dehydration- condensation reaction" can proceed, andonly after then the animals could be originated. When the Pco2 of atmosphere fell below 0. 01 atmosphere,i. e., only up to Devonian, the crust of clay minerals and soil layer and plants on land could appear, and only after then the animals can extend from seawater to land. Following the Pco2-falling further in the atmosphere, air temperature dropped down and the output of plant-food was reduced, causing further evolutionof animals into small sized, little-eating, quick-moving, and having other superior abilities to live.