Final answer:
The 3 million-year-old footprints discovered at the site of Laetoli in East Africa were made by Australopithecus afarensis, a finding by Mary Leakey. The White Sands 'ghost tracks' are more recent, dating between 21,000 to 23,000 years old, indicating an early human presence in North America.
Step-by-step explanation:
The footprints mentioned as being 3 million years old were made by the hominin species known as Australopithecus afarensis. This discovery was made by English paleoanthropologist Mary Leakey in the 1980s at the site of Laetoli in East Africa. The trail consisted of footprints left in volcanic ash that had solidified over time, indicating a modern striding gait and providing significant evidence of early hominin bipedalism. As for the 'ghost tracks' in White Sands National Park, they are estimated to be between 21,000 to 23,000 years old, and they suggest an earlier human presence in North America than previously thought, during the last Ice Age.