Have You Had Your Selenium Today?

A group of Australian scientists have recently proposed that a severe depletion of selenium levels in the world’s oceans might have been a significant factor in three of the five mass extinction events over the last 550 million years.1 This, along with other data showing that both minimal and maximal amounts of selenium are essential to sustain animal life, suggests that selenium levels must be fine-tuned.

Selenium is a trace element essential for all animal life. The Office of Dietary Supplements of the National Institutes of Health (NIH) reports that selenium “is a constituent of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection.”2 The human body contains about 15 milligrams of selenium. Since too little selenium can lead to disease and even death, the NIH recommends a daily allowance of 0.055 mg of selenium from foods such as bread, grain, fish, meat, and eggs.

Yet too much selenium can also be harmful. According to News Medical, a British news organization, as little as 5 mg of selenium a day can be toxic for humans.3 (Selenium poisoning is generally not a concern since a person would have to consume selenium-containing foods in extreme excess to reach toxic levels.)

Current levels of selenium in the oceans range from about 60 to 200 parts per trillion (PPT) depending on geographic location and depth. The Australian scientists have projected that selenium levels dropped to about 1 PPT around the time of the three mass extinction events mentioned above. Of course, these scientists did not have access to ancient seawater samples. Instead they determined the selenium concentration of 182 black shale samples that were age-dated and identified as having originated in ancient oceans over the last 550 million years. The researchers established a numerical relationship between the selenium levels in these samples and that of seawater in order to generate their projections. During much of the last 550 million years, the projected selenium levels in seawater were roughly consistent with today’s levels, except during the time of the three mass extinction events.

Both too much selenium and too little can harm us, yet Earth today seems fine-tuned to provide the just-right amount for life. Recall the words of Psalm 104:29–30:

When you hide your face, they are terrified; when you take away their breath, they die and return to the dust. When you send your Spirit, they are created, and you renew the face of the ground.

Is it a coincidence that our habitat now has the just-right amount of selenium to support advanced life? In whatever way past extinction events happened, they do appear to be part of God’s plan to prepare Earth for advanced life.

To read more about mass extinctions, see these RTB resources:




  1. John A. Long et al., “Severe Selenium Depletion in the Phanerozoic Oceans as a Factor in Three Global Mass Extinction Events,” Gondwana Research (forthcoming), published electronically October 17, 2015, doi: 10.1016/j.gr.2015.10.001.
  2. “Selenium: Dietary Supplement Fact Sheet,” National Institutes of Health, last modified July 2, 2013, https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/.
  3. “Selenium Toxicity,” News Medical, last modified February 1, 2011, http://www.news-medical.net/health/Selenium-Toxicity.aspx.


By Kirby Hansen
Kirby Hansen is a certified RTB apologist and president of the RTB San Jose, CA Chapter. He holds an MS in communications engineering from the Naval Postgraduate School and an MBA from the Stanford Graduate School of Business.


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