1 . Scientists have solved a puzzle about modern humans, after research showed that a famous skull of a human ancestor found in South Africa is a million years older than experts thought. This discovery has changed what we know of human history.
The skull, which scientists have named “Mrs Ples”, is from an ape-like human relative from a species called Australopithecus africanus (南方古猿). It was found near Johannesburg in 1947 and, based on evidence from its surroundings, was thought to be between 2. 1 and 2. 6 million years old. This puzzled scientists, because although Mrs Ples looks like a possible early ancestor of early humans, the first true humans had already evolved by the time she apparently lived. For this reason, scientists had decided that Australopithecus afarensis, a similar species from East Africa that lived about 3.5 million years ago, was our most likely ancestor instead.
To get a more accurate age for Mrs Ples, a team led by Professor Darryl Granger of Purdue University in Indiana, US, used a new method to date the sandy rocks where the skull lay. They measured the amount of certain chemicals in rocks, which form at a steady rate when they are exposed to cosmic rays (宇宙射线) on Earth’s surface. Once rocks are buried, these chemicals stop forming and slowly disappear;the surviving amount reveals how much time has passed since the rock (or bones) were on the surface.
The new study shows that Mrs Ples and other australopithecine bones nearby are between 3.4 and 3.7 million years old. This means they lived at the same time as their East African relatives, so that either group could have given rise to modern humans. However, team member Dr Laurent Bruxelles pointed out that over millions of years, at only 2,500 miles away, these groups had plenty of time to travel and to breed with each other. In other words, the groups could quite easily have met, had children together and both been part of the history of modern humans.
1. What can we learn about Mrs Ples from the first two paragraphs?| A．It is a skull found in East Africa. |
| B．It is the most possible ancestor of humans. |
| C．It is a million years older than scientists expected. |
| D．It is proved to live between 2.1 and 2.6 million years ago. |
| A．By studying the effect of cosmic rays. |
| B．By calculating the forming rate of chemicals. |
| C．By locating the sandy rocks where the skull lay. |
| D．By measuring the surviving amount of chemicals. |
| A．Modern humans came into being in East Africa. |
| B．Mrs Ples travelled and had children with East African relatives. |
| C．The history of modern humans might begin 3.5 million years ago. |
| D．Ape-like species from Africa could have interacted with each other. |
| A．Historical Puzzle Unsolved | B．Ancestor Mystery Solved |
| C．Mrs Ples: The Earliest Human Being | D．Mrs Ples: A Famous Skull |
