Question: When was the scientist that  revealed by means of microscopy the previously unknown world of microorganisms born?

Context paragraphs:
John Callion: John Cragg Callion is an award-winning British ornithologist.  His 25-year study of the European stonechat and his findings on the Eurasian dotterel have revealed much previously unknown information about both species.

Alfred Kahl: Alfred Detlef Fritz Kahl (18 February 1877 – November, 1946) was a German schoolteacher who took up microscopy in mid-life and became a leading authority on ciliated protozoa.  In a burst of scientific productivity that lasted just nine years, he published 1800 pages of scholarly work, in which he described 17 new ciliate families, 57 genera, and about 700 previously unknown species.  During his brief career as a protozoologist, he redescribed and illustrated nearly all the species of ciliates known in his time, and fit them into a taxonomic scheme that remains influential today.

History of biology: The history of biology traces the study of the living world from ancient to modern times.  Although the concept of "biology" as a single coherent field arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to ayurveda, ancient Egyptian medicine and the works of Aristotle and Galen in the ancient Greco-Roman world.  This ancient work was further developed in the Middle Ages by Muslim physicians and scholars such as Avicenna.  During the European Renaissance and early modern period, biological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms.  Prominent in this movement were Vesalius and Harvey, who used experimentation and careful observation in physiology, and naturalists such as Linnaeus and Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms.  Antonie van Leeuwenhoek revealed by means of microscopy the previously unknown world of microorganisms, laying the groundwork for cell theory.  The growing importance of natural theology, partly a response to the rise of mechanical philosophy, encouraged the growth of natural history (although it entrenched the argument from design).

Egerton Gospel: The Egerton Gospel (British Library Egerton Papyrus 2) refers to a collection of three papyrus fragments of a codex of a previously unknown gospel, found in Egypt and sold to the British Museum in 1934; the physical fragments are now dated to the very end of the 2nd century CE.  Together they comprise one of the oldest surviving witnesses to any gospel, or any codex.  The British Museum lost no time in publishing the text: acquired in the summer of 1934, it was in print in 1935.  It is also called the Unknown Gospel, as no ancient source makes reference to it, in addition to being entirely unknown before its publication.  The fragmentary manuscript forms part of the Egerton Collection in the British Library.  A fourth fragment of the same manuscript has since been identified in the papyrus collection of the University of Cologne.

Antonie van Leeuwenhoek: Antonie Philips van Leeuwenhoek ( , ] ; 24 October 1632 – 26 August 1723) was a Dutch businessman, scientist, and one of the notable representatives of the Golden Age of Dutch science and technology.  A largely self-taught man in science, he is commonly known as "the Father of Microbiology", and often considered to be the first acknowledged microscopist and microbiologist.  Van Leeuwenhoek is best known for his pioneering work in the field of microscopy and for his contributions toward the establishment of microbiology as a scientific discipline.

Age of Discovery: The Age of Discovery or the Age of Exploration from the end of the 15th century to the 18th century, was an informal and loosely defined European historical period marking the time period in which extensive overseas exploration emerged as a powerful factor in European culture and the beginning of globalization.  It also marks the rise of the period of widespread adoption in Europe of colonialism and mercantilism.  Many lands previously unknown to Europeans were discovered during this period, though most were already inhabited.  From the perspective of many non-Europeans, the Age of Discovery marked the arrival of invaders from previously unknown continents.

M J Whelan: Michael J. Whelan HonFRMS FRS (born 2 November 1931) is a British scientist.  He and Archibald Howie won the 1988 Hughes Medal of the Royal Society "for their contributions to the theory of electron diffraction and microscopy, and its application to the study of lattice defects in crystals".  He also received the 1998 Distinguished Scientist Award in Physical Sciences from the Microscopy Society of America and the 1965 C.V. Boys Prize from the Institute of Physics.

The Valachi Papers (book): The Valachi Papers is a biography written by Peter Maas, telling the true story of former mafia member Joe Valachi, a low-ranking member of the New York-based Genovese crime family, who was the first ever government witness coming from the American Mafia itself.  His account of his criminal past revealed many previously unknown details of the Mafia.  The book was made into a film ("The Valachi Papers"), released in 1972, starring Charles Bronson as Valachi.

Valentin Cassadine: Valentin Cassadine is a fictional character from "General Hospital", an American soap opera on the ABC network.  The character was initially conceived in 2009 by head writer Robert Guza, Jr., as a previously unknown member of the wealthy Cassadine family, looking to wreak havoc on both the Cassadine and Spencer families.  However, initial plans for the character's introduction were delayed and completely abandoned by 2010.  In 2016, it was announced that "All My Children" alumni James Patrick Stuart had joined the cast in the mystery role of Theo — who is revealed to be Valentin.  Valentin is known for being the most evil of the Cassadine sons having been disowned by his father at a very young age.  At one point, he even poisons his stepmother Helena (Constance Towers) when she tries to reach out to him for her own personal agenda.

Natural history in the Spanish New World: The exploration of the New World by Spanish explorers resulted in the discovery of numerous plants and animals previously unknown to European natural history.  The Spanish crown created institutions to facilitate the distribution of new knowledge.  The Council of the Indies and the Casa de la Contratacion functioned as repositories of knowledge and constructed methodological guidelines for empirical research.  Spanish physicians working in the New World provided detailed descriptions of the plants they encountered and conducted numerous experiments to determine the efficacy of these plants in treating diseases.  While the discussion of natural history in the Scientific Revolution tends to focus on the research of Italian and English scholars, Spain was also engaged in an active pursuit of new knowledge about the natural world.  However, the previously unknown nature of these plants forced an emphasis on empirical data as opposed to existing textual knowledge.  Furthermore, the emphasis on profitability encouraged an emphasis on the commercial applications of new plants and influenced the manner in which these plants were described.

Supporting paragraphs: History of biology Antonie van Leeuwenhoek
Answer: 24 October 1632