https://padlet.com/kkad/huzxk3wcay6bhpjf Made with a curious mind en-us 2021-09-17 12:52:46 UTC 2025-12-14 03:00:36 UTC hello@padlet.com ghou https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748607853 The creation of the universe was said to be by a big bang. The universe might have once been smaller than an atom.]]> 2021-09-17 13:03:25 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748607853 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748608012 After the Big Bang happened 200,000,000 years previous, it is said that the stars were born 13.5 billion years ago. It was said that gradually gravity pulled together huge clouds of hydrogen and helium atoms that drifted through the universe. gravity later helped form galaxies with billions of individual stars.]]> 2021-09-17 13:03:29 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748608012 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748624875 1 billion years after the Big Bang, The first supernovae probably blew up within a billion years of the Big Bang. Ever since, supernovae have been seeding the space between stars with more complex chemicals so that, although hydrogen and helium remain by far the most common elements in the Universe, there has built up a significant residue of other elements as well.]]> 2021-09-17 13:10:14 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748624875 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748633098 Our Sun was formed about 4.5 billion years ago from just such a cloud of matter. This “solar nebula” (as it is called) contracted under the pull of gravity until hydrogen atoms began to fuse at the center to form the star we call “the Sun.” Most of the solar nebula was gobbled up by the Sun, but tiny amounts of matter continued to orbit the young Sun farther out.]]> 2021-09-17 13:13:13 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748633098 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748640265 Biologists call these tiny, simple, one-celled organisms “prokaryotes,” and prokaryotes remain the most common organisms on Earth even today. Like all prokaryotes, the first living organisms would have been too small to see. But they could do all the things that make living organisms so different from dead matter.]]> 2021-09-17 13:15:49 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748640265 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748648238 The appearance of eukaryotes marks the appearance of a new level of complexity. Eukaryotes, like prokaryotes, were single-celled organisms. But they were mostly larger than prokaryotes, and they protected their DNA in a central nucleus. This ensured that they reproduced more accurately. Some also began to swap bits and pieces of DNA before reproducing, which meant that their offspring shared the qualities of both parents. This was the beginning of a new formof reproduction that we call “sexual reproduction.”]]> 2021-09-17 13:18:35 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748648238 ghou https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748659267 One of the most momentous of all changes in the history of our biosphere was the appearance, about 600 million years ago, of the first multi celled organisms. In the Ediacaran era and then in the Cambrian era, there suddenly appear large fossils that can be seen with the naked eye. From
then on, although most organisms still were single-celled prokaryotes or eukaryotes, paleontologists can trace the appearance of an increasing variety of multi-cellular organisms. ]]> 2021-09-17 13:22:31 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748659267 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748663448 It was probably an asteroid impact that wiped out most species of dinosaurs about 65 million years ago. The earliest mammals were probably small, burrowing creatures a bit like shrews. Their small size and nocturnal habitats may have helped them survive the terrors of an asteroid impact better than the larger dinosaurs.]]> 2021-09-17 13:23:57 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748663448 ghou https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748673367 Within the last 20 million years some primates, early forms of “apes,” began to spend more time living on the ground.]]> 2021-09-17 13:27:24 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748673367 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748674236 About 7 million years ago, somewhere in Africa, some apes began to stand on two legs. These were the first “homi- nines,” bipedal apes that were our immediate ancestors.]]> 2021-09-17 13:27:43 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748674236 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748677202 She belonged to the hominine group known as “Australopithecines” and lived about 3 million years ago in what is today Ethiopia in Africa. We can tell from the way her spine is attached to her skull that Lucy was bipedal.]]> 2021-09-17 13:28:47 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748677202 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748692233 Two million years ago, in east Africa, there appeared another hominine species, known as Homo habilis. What made this species different was that its members could manufacture simple stone tools.]]> 2021-09-17 13:34:07 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1748692233 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755275523 Within a half million years, there appeared another hominine species, Homo ergaster, or Homo erectus (paleontologists still argue about the exact terminology). Members of this species were about the same size as us and had brains almost as large as ours. They also made stone tools more sophisticated than those of Homo habilis. Some members of this species left Africa and migrated, over many generations, as far as China.]]> 2021-09-20 20:33:44 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755275523 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755280141 Our own species, Homo sapiens, appeared about 250,000 years ago, probably somewhere in east Africa. With our appearance we enter the domain of human history.]]> 2021-09-20 20:36:26 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755280141 kkad https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755320892 After about 380,000 years it underwent another “phase change.” It cooled enough for positively charged protons to capture negatively charged electrons, there by forming the first atoms. These were electrically neutral, so quite suddenly matter ceased to interact with electromagnetic radiation. The energy released at this point in the Universe’s history can still be detected today in the so-called cosmic background radiation.]]> 2021-09-20 20:58:51 UTC https://padlet.com/kkad/huzxk3wcay6bhpjf/wish/1755320892