text: // define the data url
  var earthquake_url = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson"
  
  // define the cuntion of marker size
  function markerSize(magnitude) {
      return magnitude * 4;
  };
  
  var earthquake = new L.LayerGroup();
  //// Retrieve the data
  d3.json(earthquake_url, function (geoJson) {
      L.geoJSON(geoJson.features, {
          pointToLayer: function (geoJsonPoint, latlng) {
              return L.circleMarker(latlng, { radius: markerSize(geoJsonPoint.properties.mag) });
          },
  
          style: function (geoJsonFeature) {
              return {
                  fillColor: Color(geoJsonFeature.properties.mag),
                  fillOpacity: 0.7,
                  weight: 0.1,
                  color: 'black'
  
              }
          },
      }
  }