{"id":4574,"date":"2022-08-05T10:00:00","date_gmt":"2022-08-05T10:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=4574"},"modified":"2022-07-20T08:12:53","modified_gmt":"2022-07-20T08:12:53","slug":"when-did-the-first-fish-live-on-earth-and-how-do-scientists-figure-out-the-timing","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/when-did-the-first-fish-live-on-earth-and-how-do-scientists-figure-out-the-timing\/","title":{"rendered":"When did the first fish live on Earth \u2013 and how do scientists figure out the timing?"},"content":{"rendered":"\n
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\n Reconstruction of Haikouichthys ercaicunensis<\/em> based on fossil evidence.\n Talifero\/Wikimedia Commons<\/a>, CC BY-SA<\/a><\/span>\n <\/figcaption>\n <\/figure>\n\nIsaac Skromne<\/a>, University of Richmond<\/a><\/em><\/span>\n\n
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Curious Kids<\/a> is a series for children of all ages. If you have a question you\u2019d like an expert to answer, send it to curiouskidsus@theconversation.com<\/a>.<\/em><\/p>\n\n

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How do you figure out how long ago fish were created? Hundreds of millions of years is a long time ago. \u2013 Josh, age 11, Ephrata, Pennsylvania<\/strong><\/p>\n<\/blockquote>\n\n

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The oldest fossils of animals resembling a fish<\/a> date back between 518 million and 530 million years ago. Discovered in China and called Haikouichthys<\/em>, these animals were about an inch long (2.5 cm) and had a head with seven to eight slits at its base that looked like gills<\/a>. They also had a distinct spine surrounded by muscles<\/a>. <\/p>\n\n

But there are ways Haikouichthys<\/em> did not resemble any modern fish. For example, they didn\u2019t have a jaw<\/a>. Instead, their mouth was a cone-like opening similar to the ones seen in modern hagfish and lampreys<\/a>. They also appear not to have had side fins<\/a>.<\/p>\n\n

Even though scientists like me<\/a> weren\u2019t around to see for ourselves what was happening on Earth so long ago, we use geologic clues to figure out what animals lived when. Here\u2019s how we sort out very ancient timelines and even put dates on fossils like Haikouichthys<\/em>.<\/p>\n\n

Measuring in the millions<\/h2>\n\n

To figure out how long ago fish first appeared on Earth you need a way to measure really, really long time intervals. Clocks measure short intervals, like seconds, minutes and hours. Calendars measure longer intervals, like days, months and years. What can you use to measure millions of years?<\/p>\n\n

Radiometric dating<\/a> is the method that scientists use to calculate the passage of time in millions of years. To determine the age of rocks and fossils, scientists measure the type of atoms they are made of. <\/p>\n\n

You might know that atoms are the building blocks of molecules, which make up everything around you<\/a> \u2013 grass, cement, even air. While most atoms are very stable, some, called radioactive atoms, are unstable<\/a>. Over long periods of time, they spontaneously break down into more stable atoms. <\/p>\n\n

Uranium is one of these radioactive atoms. It breaks down very slowly into lead<\/a>. Both uranium and lead atoms can be found naturally in rocks and minerals<\/a> in very, very low amounts. <\/p>\n\n

Nuclear physicists have calculated that it would take 700 million years for one pound of uranium<\/a> to break down into half a pound of lead. This rate of decay occurs at such a predictable rate that scientists can use it to calculate fairly accurately how old rocks and fossils are.<\/p>\n\n

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\n Ernest Rutherford at McGill University, 1905.<\/span>\n Unknown, published in 1939 in ‘Rutherford: being the life and letters of the Rt. Hon. Lord Rutherford’\/Wikimedia Commons<\/a>, CC BY<\/a><\/span>\n <\/figcaption>\n <\/figure>\n\n

The idea for radiometric dating first occurred to a New Zealand scientist named Ernest Rutherford<\/a> in 1904. His idea was to measure the number of uranium atoms and lead atoms in a rock and compare them. He predicted that an older rock would have more lead and less uranium than a younger rock would.<\/p>\n\n

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\n Unstable atoms turn into stable atoms over time at a steady and predictable pace.<\/span>\n NOAA<\/a><\/span>\n <\/figcaption>\n <\/figure>\n\n

The American scientist Bertram Boltwood<\/a> put Rutherford\u2019s idea to the test, measuring the amount of uranium and lead in different rocks<\/a> collected from all over the world. <\/p>\n\n

Once a rock is formed, no new elements are added to it. So scientists can calculate how much uranium the rock started with by adding what\u2019s left to the amount of lead that\u2019s there now, thanks to the radioactive decay process. Then, because they know exactly how long it takes for uranium to break down into lead, they can figure out the age of the rock. Boltwood proved that Rutherford\u2019s idea worked, establishing the field of radiometric dating in 1907.<\/p>\n\n

The making of the Haikouichthys<\/em> fossil<\/h2>\n\n

Fossils are rocks<\/a>. So scientists can use radiometric dating to estimate how long ago the organisms that left the fossil imprint lived on Earth. <\/p>\n\n

Animals leave fossil imprints only under special circumstances. In order for the Haikouichthys<\/em> to leave fossils, their dead bodies would have had to sink to the bottom of the water and be covered with sediments before microorganisms could decompose them. Then, minerals in the sediments would have seeped into the Haikouichthys<\/em> for their remains to become fossilized. <\/p>\n\n

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\n A nearly complete specimen of Haikouichthys<\/em> with the eye and zigzag-shaped muscle fibers called myomeres visible. This is one of many Haikouichthys<\/em> fossils discovered in China.<\/span>\n Dr. and Prof. Degan Shu, Shannxi Key Laborotory of Early Life and Envionment Department of Geology, Northwest University<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\n

Radiometric dating of Haikouichthys<\/em> fossils suggests these animals were swimming in Earth\u2019s waters between 518 million and 530 million years ago<\/a> \u2013 and possibly longer. <\/p>\n\n

Earth\u2019s age as a 24-hour day<\/h2>\n\n

Scientists, using radiometric dating, estimate the Earth itself is 4.5 billion years old<\/a>. For a long time on Earth, there was no life at all. Then microorganisms like bacteria showed up. It\u2019s only relatively recently that plants and animals began living on Earth.<\/p>\n\n

In fact, if you think of Earth\u2019s age until now as a 24-hour day, it turns out Haikouichthys<\/em> lived 2 hours and 45 minutes before the end of the day. Humanlike animals<\/a> appeared even more recently on Earth \u2013 about 5 million to 7 million years ago <\/a> \u2013 only a few minutes before the end of the hypothetical day. <\/p>\n\n

Whether the Haikouichthys<\/em> was the first fish or not remains controversial. There are very few other fishlike fossils from the same time period. But paleontologists keep digging. Who knows, maybe in a few years they will discover an even older fishlike animal that will dethrone Haikouichthys<\/em> as the oldest fishlike creature.<\/p>\n\n

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Hello, curious kids! Do you have a question you\u2019d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com<\/a>. Please tell us your name, age and the city where you live.<\/em><\/p>\n\n

And since curiosity has no age limit \u2013 adults, let us know what you\u2019re wondering, too. We won\u2019t be able to answer every question, but we will do our best.<\/em>\"The<\/p>\n\n

Isaac Skromne<\/a>, Assistant Professor of Biology, University of Richmond<\/a><\/em><\/span><\/p>\n\n

This article is republished from The Conversation<\/a> under a Creative Commons license. Read the original article<\/a>.<\/p>\n\n","protected":false},"excerpt":{"rendered":"Reconstruction of Haikouichthys ercaicunensis based on fossil evidence. Talifero\/Wikimedia Commons, CC BY-SA Isaac Skromne, University of Richmond Curious…\n","protected":false},"author":153,"featured_media":4575,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","fifu_image_url":"","fifu_image_alt":"","footnotes":""},"categories":[13,17,11],"tags":[234,25,474],"class_list":{"0":"post-4574","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-earth","8":"category-math-and-the-sciences","9":"category-nature","10":"tag-geology","11":"tag-paleontology","12":"tag-the-conversation","13":"cs-entry","14":"cs-video-wrap"},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/posts\/4574","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/users\/153"}],"replies":[{"embeddable":true,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/comments?post=4574"}],"version-history":[{"count":1,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/posts\/4574\/revisions"}],"predecessor-version":[{"id":4576,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/posts\/4574\/revisions\/4576"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/media\/4575"}],"wp:attachment":[{"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/media?parent=4574"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/categories?post=4574"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/modernsciences.org\/staging\/4414\/wp-json\/wp\/v2\/tags?post=4574"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}