He was the first to use the term "cell"

Hooke published Micrographia, the first scientific blockbuster ever in 1665 when he was 30 years old. Micrographia showed a brand-new universe that no one had ever thought was possible. The book served as a display of Hooke's unique capabilities, including his grasp of nature and light, his highly developed scientific instruments, construction skills, and his abilities as an artist.

Hooke created a novel, screw-operated focusing mechanism and built a compound microscope with it. Before, the specimen had to be moved to be in focus. He added illumination to the microscope to make it even better. To brilliantly illuminate his specimens, he set up an oil lamp next to the microscope and a water lens to concentrate the light on it.

Hooke examined the tiniest, hitherto unnoticed aspects of the natural world with his microscope. In the form of tiny fungus, Hooke found the first known microorganisms in 1665. This came nine years before Antonie van Leeuwenhoek discovered single-celled life. Hooke examined the microscopic structure of the cork tree's bark. In the process, he discovered and gave the term "cell" to the basic unit of life. He believed the things he had found resembled the distinct cells, or chambers, found in monasteries. Hooke never identified the real biological purpose of cells.

Besides, Hooke examined the ancient cells in the petrified wood with his microscope. He concluded that fossils were once living organisms whose cells had become minerals. He also concluded that certain extinct species must have previously existed. Although practically everyone today accepts this, his proposition was unpopular when it was first presented. According to Hooke's Micrographia: "Nothing is so far away that it cannot be seen through the use of telescopes, and nothing is so little that it cannot be studied through the use of microscopes. As a result, a new visible World has been made known to humankind."