Final answer:
The intense interest in Mars prior to the space age was driven by the hopes of finding life there, influenced by mythic notions like the martian canals, and by the desire to understand the cosmic origins. Notable figures like Percival Lowell were instrumental in popularizing the idea of a Martian civilization. Despite the Mariner 4 photos revealing a barren landscape, interest in Mars as a repository of answers to universal questions remained strong.
Step-by-step explanation:
The principal cause of our intense interest in Mars in the decades before the dawn of the space age was largely due to the speculation about the possibility of life on Mars and the further imageries of the planet, which included the infamous martian canals. Imaginations were further fueled by figures like Percival Lowell, who ardently proposed the existence of an intelligent Martian civilization. Even though Mariner 4's photographs depicted Mars as a 'dead planet' with abundant impact craters, it did not significantly dampen human curiosity.
Additionally, the quest to understand the origin of the universe and the solar system provoked people's interest in Mars as a planet which might have shared a similar history to Earth, especially in its early years. Theories about the parallels in conditions on Mars and Earth around the time of the emergence of life on our planet highlighted the prospect that Mars might have harbored life at some point, a hypothesis that has continued to propel scientific exploration.
In any case, the early fascination with Mars speaks to humanity's broader aspirations for space exploration and our quest for understanding our place in the cosmos, enriching our global perspective and deepening our appreciation for Earth.