👉 The first blood cells appeared in ancient sponges around 600 million years ago, evolving from precursor cells that allowed for basic circulation. Their early forms were larger than modern red and white blood cells but played pivotal roles in defense and oxygen transport. To complete this under 200 words: Ancient sponges gave rise to the earliest known blood cells—protoblasts—that began circulating fluids, initiating rudimentary immune responses and oxygen exchange around 600 million years ago. These primitive cells laid groundwork for complex hematopoiesis in later organisms.
